WORLD METEOROLOGICAL ORGANIZATION WMO TROPICAL METEOROLOGY … · tropical and extratropical meteorology. The acceleration of a tropical cyclone into the midlatitudes leads to an

WORLD METEOROLOGICAL ORGANIZATION

WMO TROPICAL METEOROLOGY RESEARCH PROGRAMME (TWRP) COMMISSION OF ATMOSPHERIC SCIENCES (CAS)

PROCEEDINGS OF THE INTERNATIONAL WORKSHOP ON TROPICAL/EXTRATROPICAL INTERACTIONS

INCORPORATING THE THIRD INTERNATIONAL WORKSHOP ON EXTRATROPICAL TRANSITION

(PERTH, AUSTRALIA)

5-9 DECEMBER 2005

Sectratariat of the World Meteorological Organization Geneva, Switzerland

2006

TABLE OF CONTENTS

TABLE OF CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 CHAPTER 1: INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 CHAPTER 2: ORGANIZATION OF THE WORKSHOP . . . . . . . . . . . . . . . . . . . . . . . 7 CHAPTER 3: RECENT PROGRESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 CHAPTER 4: DOWNSTREAM IMPACTS OF EXTRATROPICAL TRANSITION . . . . 13 CHAPTER 5: DIRECT IMPACTS OF EXTRATROPICAL TRANSITION . . . . . . . . . . . 19 CHAPTER 6: RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 APPENDIX A: Agenda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 APPENDIX B: PARTICIPANTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

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PREFACE

A poleward-moving tropical cyclone often undergoes extratropical transition that may result in the formation of a rapidly-moving and deepening extratropical cyclone. These cyclones are associated with an expanding field of tropical storm-force winds, heavy precipitation, and high seas over high-latitude coastal and oceanic regions. Over recent years, several high-impact events have focused attention on the environmental and societal impacts due to the extratropical transition of tropical cyclones. The complex physical and dynamical processes that occur during extratropical transition have been topics of concentrated research programs. Because of the impacts and research interests in extratropical transition, a series of workshops have been held to provide a forum by which researchers and forecasters could discuss scientific issues and forecast requirements with respect to extratropical transition. This third meeting of the WMO International Workshop on Extratropical Transition (IWETIII) was held under the auspices of the WMO CAS Working Group on Tropical Meteorology Research (WGTMR), chaired by Professor Lianshou Chen, and the series of International Workshops on Tropical/Extratropical Interactions. At the kind invitation of the Government of Australia, IWETIII was held on 5-9 December 2005 in Perth Australia. In addition the outstanding hospitality to all participants, the Australian Government Bureau of Meteorology provided a CD of all presentations made at the Workshop.

The scientific objectives of IWETII were to assess progress on recommendations from the Second International Workshop on Extratropical Transition (IWETII), examine current forecast issues, and present new research findings. The role of extratropical transition on midlatitude predictability was addressed as it is a focus of the WMO/World Weather Research Program (WWRP) titled The Observing System Research and Predictability Experiment (THORPEX). A goal of IWETIII was to provide a modified list of recommendations for forecast and research priorities related to extratropical transition.

Presentations at IWETIII (Appendix A) were from a diverse group of researchers and forecasters that represented nearly every forecast center, ocean basin and midlatitude region that experiences extratropical transition. A brief summary of the Workshop organization is provided in Chapter 1. Chapter 2 contains a summary of the progress made since IWETII. Chapter 3 contains summaries of the major issues presented and discussed during each session. The priorities and recommendations for future research- and forecast-related issues are summarized in Chapter 4. Many thanks go to all the participants for preparation, submission, presentation, and discussion of research results and forecast issues. Each session was expertly chaired in such a manner that encouraged and guided lively discussion of many important topics. Contributions from all participants contributed to a very successful Workshop.

Finally, many thanks are extended to the Australian Government, Bureau of Meteorology for hosting the Workshop. Special thanks are extended to the Local Organizing Committee led by the Perth Office of the Bureau of Meteorology for very efficient assistance in preparation and execution of the Workshop

Jim Abraham and Gary Foley Co-Organizers, IWETIII

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CHAPTER 1

INTRODUCTION

The poleward movement and extratropical transition (ET) of a tropical cyclone (TC) initiates complex interactions with the midlatitude environment that often results in a high-impact midlatitude weather system with strong winds, high seas, and large amounts of precipitation. A cyclone undergoing ET may pose a serious threat by extending tropical-cyclone-like conditions over a larger area, bringing the strong winds typical of major winter storms to midlatitudes during summer or autumn. Although these extreme conditions severely impact the region of the ET, there are often significant impacts that occur downstream of an ET event. These impacts may be due to the excitation of large-scale propagating Rossby wave-like disturbances that can substantially modify the midlatitude flow downstream.

Extratropical transition poses a significant challenge to the forecaster. Numerical forecasts of ET are not yet reliable, which introduces large uncertainties in the predictions of the timing of the increased translation speed, the potential for rapid re-intensification as an extratropical cyclone, the severity of the weather, and the impact on the weather downstream. Often, there is a decrease in forecast skill across the Northern Hemisphere (Figure 1) during an ET event as occurred during Typhoon (TY) Nabi and TY Saola over the western North Pacific and Hurricane Maria over the North Atlantic in September 2005. Such decreases in forecast skill associated with ET are common to all numerical weather prediction models. The challenges involved in forecasting and understanding ET contain elements of both tropical and extratropical meteorology. The acceleration of a tropical cyclone into the midlatitudes leads to an expansion and increased asymmetry in the wind field, which contributes to rapid growth in ocean-surface wave heights. Due to the interaction between the decaying tropical cyclone and the midlatitude westerlies, increased translation speed during ET results in a decreased warning time for hazardous weather. Furthermore, if the timing is misjudged, large errors in the forecast track may result. Typically, the movement of a tropical cyclone into the midlatitudes is accompanied by a decrease in intensity. However, the interaction with an extratropical system during ET may result in rapid re-intensification of the decaying tropical cyclone as an extratropical cyclone. This major forecast challenge is complicated by the fact that the interpretation of satellite imagery appropriate for a tropical cyclone would suggest that the system is weakening. During ET, the forcing of ascent by the large-scale midlatitude flow influences the expansion of the region of heavy precipitation away from the center of the decaying tropical cyclone to regions that typically extend poleward and downstream of the circulation center. Thus, heavy precipitation extends over a larger area such that heavy precipitation can occur over land without the tropical cyclone making landfall. Because large amounts of precipitation may fall over an area ahead of the decaying tropical cyclone center, the ground may be saturated prior to the arrival of the precipitation surrounding the remnant tropical cyclone center. Due to the change in the mechanisms responsible for the development of precipitation, current operational techniques for quantitative precipitation forecasting are often inadequate during ET. Furthermore, the increased asymmetry in precipitation and wind fields can lead to the

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strongest winds being associated with dry air. Over locations such as southwest Australia, this enhances the hazard from bush fires.

TY Nabi TY Saola

Figure 1 Anomaly correlation for 120-h forecasts of 500 hPa height over the Northern Hemisphere for the National Centers for Environmental Prediction Global Forecast System (GFS) and the Navy Operational Global Atmospheric Prediction System (NOGAPS). The numerical prediction of ET is hindered by the difficulty in representing both the tropical cyclone and the midlatitude circulation into which it is moving. Difficulty in accurate initialization of both the tropical cyclone structure and the midlatitude flow contribute to numerical forecast errors. While current operational global models may adequately represent spatial scale sufficient to forecast the evolution of the midlatitude flow they are generally unable to represent the inner-core of a tropical cyclone. Many studies indicate that fine-scale structures associated with the inner-core of a tropical cyclone influence the ET process. Furthermore, physical processes (convection, boundary-layer processes, air-sea interaction) play a crucial role in ET and may not be represented adequately in current operational models. While regional and mesoscale models may provide better representation of the tropical cyclone structure, representation of the large-scale midlatitude circulation into which the decaying tropical circulation is moving often suffer from boundary problems. . The increase in understanding of the evolution of a tropical cyclone to an extratropical cyclone will aid forecasters responsible for tropical cyclone advisories over each basin in which ET occurs. It is also apparent that significant downstream impacts that may

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involve multiple ocean basins and continental areas are associated with ET events. Both the local and downstream impacts of ET are related to the complex interactions among varying spatial-scales (from the convective-scale inner-core of a tropical cyclone to the synoptic- to planetary-scale upper-level midlatitude troughs) and physical processes. For example, important mechanisms related to downstream impacts include forcing of a Rossby wave response by advection of vorticity due to the divergent wind from the tropical cyclone core. Also, diabatically-generated Rossby waves/vortices may result from upward motion along sloping isentropic surfaces that exist at the tropical cyclone-midlatitude interface. An important contributor to the lack of understanding and representation of the major processes during ET is that the majority of events occur over the ocean with a very limited number of in-situ observations. To increase predictability associated with ET and its downstream impacts, the importance of key in-situ observations must be established. This may result from targeted or adaptive observation strategies, which includes advancing data assimilation and ensemble-based techniques. Because of the varied physical characteristics associated with ET, a mix of data types and platforms may be required to increase predictability of ET-related weather. Based on the need for increased understanding and prediction of ET and impacts associated with ET, the WMO Commission on Atmospheric Science (CAS) Tropical Meteorology Research Program (TMPR) began a series of International Workshops on Extratropical Transition (IWET) in which the first Workshop was held in Kaufbeuren, Germany in May 1998, and the second Workshop was held in Halifax, Nova Scotia, Canada in December 2003. The purposes of this third Workshop (IWETIII) were defined as follows:

• Assess progress on recommendations from the second Workshop (IWET II); • Share forecast experience and issues together with recent research results; • Examine the impacts of ET on the predictability of the large-scale midlatitude

circulation; • Identify critical factors that are required to increase the understanding of the

impacts of ET on the predictability of the downstream midlatitude circulation; • Examine the role of ET on midlatitude predictability was addressed as it relates

to the WMO/World Weather Research Program (WWRP) The Observing System Research and Predictability Experiment (THORPEX); and

• Examine forecast techniques associated with direct ET impacts.

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CHAPTER 2

ORGANIZATION OF THE WORKSHOP

The Workshop was convened on 5 December 2005 with a welcoming address by Gary Foley, Deputy Director of the Australian Government, Bureau of Meteorology in which the agenda (Appendix A) was reviewed. As a representative of the WMO, Dr. Elena Manaenkova, Director, Atmospheric Research and Environment Program addressed the Workshop to emphasize the importance of increased understanding of ET and related impacts. Professor Chen Lianshou also addressed the Workshops participants and reviewed the importance of the various goals for the Workshop. Finally, Jim Abraham provided a summary of any progress that had been made on recommendations from IWET II. In keeping with the goals of the Workshop that have been outlined in Chapter 1, the Workshop was organized into two primary themes defined as; i) downstream impacts of ET; and ii) direct impacts of ET. Contained within each theme, are issues and perspectives based on operational forecast needs and research accomplishments and studies. During first half of the Workshop the downstream impacts of ET and the impact of ET on overall predictability of the midlatitude circulations was addressed. These sessions began with an overview of THORPEX and an introduction of the regional THORPEX activities. In particular, the proposed THORPEX program on predictability over the North Pacific was presented. Several presentations followed to address the role of ET in the THORPEX Pacific Predictability program. Continuing in the downstream impacts theme, the second day of the Workshop was divided into three main topics. Initially, representatives from several operational forecast centers discussed forecast difficulties with respect to the downstream impacts of ET. Following the forecaster perspective, several presentations on the diagnosis of downstream impacts were given. The final session on downstream impacts was dedicated to modeling studies. Days three and four of the Workshop were dedicated to direct impacts of ET. On day three, the focus was on forecaster issues and requirements. A forecaster representative from every basin that contains ET presented examples of difficult forecast situations and issues that impact their operations. These presentations were followed by two laboratory exercises that were designed to convey forecaster issues to the Workshop participants. One laboratory exercise examined the use of primary analysis products available during forecast operations and a second laboratory exercise introduced the use of the Cyclone Phase Space in applications of ET forecasting. On day four, the direct impacts of ET were discussed in the context of case studies, diagnostic studies, and modeling studies. These presentations represented cases from several regions. Also, some modeling studies were based on idealized simulations and others were directed as high-resolution simulations of specific cases. The formal sessions concluded with presentations of Dr. J. C. L. Chan, chairman of the WMO Sixth International Workshop on Tropical Cyclones (ITWC-VI) and Prof. R. L. Elsberry, Tropical Cyclone Rapporteur, WMO/CAS TMRP. These two presentations provided a framework by which ET is linked to WMO programs and topics to be addressed during IWTC-VI.

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A final plenary session was conducted to draft a list of recommendations that would be used as a guide for future research and operations that address ET. These recommendations were drafted based primarily on forecaster needs with input from the research community as to the likelihood that current and near-term research could address each issue. A total of 49 participants registered for the Workshop. Of these participants, 13 attended from Australia, 6 attended from Canada, 4 attended from China, 1 attended from Hong Kong, China, 4 attended from Germany, 1 attended from Israel, 2 attended from Japan, 1 attended from La Reunion, 1 attended from New Zealand, 1 attended from Russia, 1 attended from South Africa, 2 attended from the United Kingdom, 10 attended from the United States, and 2 attended from the WMO.

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CHAPTER 3

RECENT PROGRESS

To begin the Workshop, a review of the primary issues and recommendations of IWET II were presented. The primary issues were divided into several categories defined as;

• Tropical cyclone characteristics during ET, which includes motion, intensity, structure, and structure change;

• Remote impacts of ET; • Numerical prediction of ET events; • Operational concerns associated with ET; • Training.

In this Chapter, the primary issues associated with each category are summarized. Recommendations that address each issue are defined along with any progress that has been made in terms of addressing the issues. a. Tropical cyclone characteristics 1. Track ISSUES: The evolution of the wind, cloud, and precipitation field during ET are extremely sensitive to the timing of recurvature and subsequent acceleration into the midlatitude circulation. Forecaster experience suggests that while the overall track shape may be accurately forecast there can be large cross- and along-track error components. Cross-track errors are predominantly due to errors in the interaction of the decaying tropical cyclone and the midlatitude circulation/trough into which the decaying tropical cyclone is moving. Along-track errors are predominantly due to speed errors associated with incorrect forecasts of the acceleration of the decaying tropical cyclone into the midlatitudes. RECOMMENDATIONS: Improvements in forecasts of the storm motion during ET are required. Primarily, this improvement should occur in the operational global numerical prediction models that provide the primary guidance to forecasters during ET events. The large variability among model track forecasts, which are primarily due to along-track displacements during ET, suggests that ensemble approaches may be extremely valuable. This includes multi-model models that would provide a consensus-type of forecast and within-model ensembles that measure the uncertainty in the forecasts of a specific model PROGRESS: Over recent years, tropical cyclone track forecasts based on multi-model consensus forecasts have exhibited significant skill during all phases of a tropical cyclone life cycle. Furthermore, recent studies using within model ensemble forecasts suggest that the individual members may not provide as comprehensive a measure of forecast variability.

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2. Intensity ISSUES: During ET, intensity may be defined by any one of the severe weather factors associated with ET. These include the central sea-level pressure, maximum wind speed, or maximum rainfall. Intensity forecasts during ET are very sensitive to the track forecasts and primarily the speed of motion along the track that define the phasing between the decaying tropical cyclone and the midlatitude circulation into which it is moving. Furthermore, it must be recognized that there are complex physical mechanisms associated with the decay of the tropical cyclone and the re-intensification as an extratropical cyclone. Often, the resulting extratropical cyclone will have a greater intensity than the original tropical cyclone. RECOMMENDATIONS: There is a need to systematically quantify weakening rates of TCs moving over cold water or into regions of increased vertical wind shear in a baroclinic environment. Because in-situ measurements of important intensity-related parameters are not routinely possible during ET, remotely-sensed measurements of parameters such as the expansion of the low-level wind distribution, coverage and rate of precipitation, and overall thermal structure must be explored. Based on combinations of measurements, conceptual models of the tropical cyclone decay and re-intensification as an extratropical cyclone may be constructed. These conceptual models may then be applied to operational numerical model forecasts in terms of calibration and assessment of the numerical guidance. PROGRESS: Since IWET II there have been some high-resolution modeling studies that have provided diagnostic analyses of various factors associated with intensity during ET events. However, a basic lack of understanding in the rates and patterns of variability associated with many important intensity factors remains.

3. Structure and structure change ISSUES: Several studies have documented the structural changes associated with the decaying tropical cyclone and the re-intensification as an extratropical cyclone. These changes impact the wind field, which is observed to expand; the cloud field, which is observed to become quite asymmetric; and the precipitation patterns, which also expand in an asymmetric manner. There are important unresolved issues that include the timing, severity, and duration of the structural changes. Furthermore, changes in parameters such as the ocean wave field have rarely been documented. Many of the details associated with the changes to important structural changes will be due to the interaction with the midlatitude circulation into which the tropical cyclone is moving. RECOMMENDATIONS: A systematic examination of structural changes must be initiated via case studies of a wide variety of ET types. These investigations should incorporate microwave and scatterometer satellite data for identification of structural changes during ET. The impacts due to the change in ocean parameters on the surface fluxes of heat, moisture, and momentum, and the feedback to the wind field distribution should be examined. Important parameters should be identified that may lead to a parameter-based statistical model of intensity that may be similar in design and implementation to established statistical models of tropical cyclone intensity. The systematic identification of structural characteristics and changes during ET should lead to construction of an application such that various important structural characteristics

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could be identified, examined, and evaluated in a routine manner as part of an operational forecast. PROGRESS: While some limited satellite studies were conducted in recent years, there remains a lack of observation-based case studies of ET events. Because ET events occur in regions of sparse standard data coverage, in-situ observations are dependent on special programs designed to observe individual cyclone events. b. Remote impacts ISSUES: There are often large impacts to the midlatitude circulation patterns that occur upstream and downstream of an ET event. Often these impacts may be due to interactions between the decaying tropical cyclone and the midlatitude circulation into which it is moving. RECOMMENDATIONS: A systematic examination of the variability in remote impacts of ET events is needed. It is often observed that some ET events have large remote impacts while others have very small remote impacts. The important characteristics that identify the occurrence, timing, and intensity of downstream impacts should be examined. PROGRESS: There have been several key studies that address the issue of remote impacts due to an ET event. Specifically, these studies have examined variability among ensemble members to identify decreased predictability of the large-scale midlatitude circulation due to ET events. Also, the sensitivity of ET events relative to various perturbations in the midlatitude flow has been examined. Several studies have identified characteristics in remote impacts due to the location, shape, and intensity of upper-level midlatitude troughs. c. Numerical weather prediction ISSUES: The impacts of the insertion of synthetic tropical cyclone observations in operational numerical forecast models as the cyclone is about to undergo ET needs to be examined. Often it appears that the insertion of a synthetic vortex imparts a tropical cyclone structure into an environment in which a decaying tropical cyclone is occurring in reality. It may be better to provide improved initial conditions via better use of observations and advances in data assimilation (e.g., 4DVAR), which may be an order of magnitude more complex than the insertion of a tropical cyclone bogus. RECOMMENDATION: There is a need for improved use of conventional and satellite data and advanced data assimilation strategies such that initial conditions associated with ET events are improved. Furthermore, additional studies are required to examine the impacts of varying observation types and strategies in an ET environment. PROGRESS: There have been some initial examinations of the role(s) of data assimilation techniques in improving initial conditions during ET. The THORPEX program will examine impacts of data distributions and observing strategies in ET. d. Miscellaneous operational issues ISSUES: There is often large spatial variability in the assignment of a location where an operational tropical cyclone forecast center declares a tropical cyclone an extratropical

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cyclone. There is also large temporal variability in the assignment of the time when a tropical cyclone is declared extratropical cyclone. These spatial and temporal variations impact the issuance of advisories and how the general public may react to the risk of severe weather. Although a decaying tropical cyclone may have moved to higher latitudes the wind speeds may remain at least at tropical storm strength. There needs to be a consistent policy associated with the transfer of forecasts of ET systems from a tropical cyclone center to other centers that may be primarily concerned with precipitation. RECOMMENDATIONS: A concentrated study is needed to compare global differences and similarities associated with the transfer of tropical cyclone-related advisories to midlatitude advisories. One web site should be produced where all guidance can be found for TC- related and ET-related issues. There is a need for a symbol and naming convention (i.e., post-hurricane Charley) that is applicable to ET. e. Training ISSUES: There are no routine venues by which the recent research results associated with ET are made aware to operational forecasters. Training on the most recent and relevant research results associated with ET will allow forecasters to more quickly assess/diagnose model data from non-traditional perspectives. For example, the cyclone phase-space diagrams developed by Prof. Robert Hart at the Florida State University might be expanded to provide quick assessments of conceptual models and impacts. RECOMMENDATION: A training module should be developed that incorporates new research associated with ET (e.g., the cyclone phase space). A comprehensive website for obtaining TC-ET information (e. g., bibliography of all ET-related articles) should be developed. A forecaster training manual (virtual or real) should be developed as done for tropical cyclone forecasting under the auspices of the International Workshop on Tropical Cyclones. PROGRESS: A COMET module has been prepared to address the use of the cyclone phase space.

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CHAPTER 4

DOWNSTREAM IMPACTS OF EXTRATROPICAL TRANSITION Based on the occurrence of recent high-impact weather events (i.e., periods of extreme precipitation, high-wind events) over coastal regions that appeared to have some degree of linkage to an upstream ET events, the initial portion of the Workshop was dedicated to downstream impacts of ET. Because of the relationship between ET events and midlatitude predictability over synoptic-scale time and space scales, a connection between ET and THORPEX had begun to develop since IWET II. Therefore, the Workshop began with several presentations that defined the overall THORPEX program and goals, regional THORPEX activities. a. THORPEX As manager of the THORPEX International Program Office, Dr. David Burridge provided an overview of THORPEX. Established as a ten-year international research and development effort, the primary THORPEX goal is to increase the accuracy of one day to two week forecasts of high-impact weather events for the benefit of society, the economy, and the environment. THORPEX is part of the WMO World Weather Research Program. Furthermore, THORPEX provides a framework for international collaboration among operational centers and academic institutions, developing and developed nations, and research scientists and forecasters. A goal of THORPEX is the development of a global integrated forecast system that would generate probability-based decision support tools for all nations. The THORPEX overview continued as Dr. M. Shapiro presented several examples of high-impact weather events that often had common underlying large-scale dynamical factors that often occur on global spatial scales. Several cases highlighted the importance of the relative roles of tropical cyclones and ET in contributing to high-impact events over regions far from the direct influence of the event. Furthermore, the role of THORPEX was emphasized as being a bridge between increased accuracy related to forecasts of high-impact weather events and climate, which defines the basic atmospheric state that influences many dynamical aspects of high-impact weather events. Following the THORPEX overviews, representatives of several regional THORPEX committees reported on progress and plans in their respective locations. The North-American THORPEX committee report, which was represented by Dr. D. Parsons and Dr. P. Gauthier, also provided several examples of high-impact weather events that had similar underlying dynamical properties. During a specific period (Figure 2), several flood, fire, and tropical cyclone events over North America were related to large-scale Rossby-wave packets that had a dynamical connection to tropical cyclone and large-scale convection over the western North Pacific. Results from a previous THORPEX campaign for evaluation of targeted observation strategies over the North Atlantic were presented to show a small positive influence on forecast skill over Europe due to the

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A

B

C

Figure 2 Time-longitude diagram of meridional wind at 250 hPa during October, 2003. The dashed diagonal lines identify wave packets that originated in the area contained in the box between 60oE and 120oE. In the downstream box located at 120oW, the letter defines the time and longitude of high-impact weather events associated with the wave packet. These events include, (A) severe floods in British Columbia, Canada, (B) severe floods in Seattle, WA, USA, and (C) wild fires associated with strong downslope winds in southern California USA. This figure was generated using the NOAA Climate Diagnostics Website (www.cdc.noaa.gov). placement of targeted observations over the North Atlantic. Based on the evidence of a dynamical linkage between the western North Pacific and high-impact weather events over North America, and the modest success of the Atlantic THORPEX campaign, the North American committee is proposing a campaign of increased observations targeting convection, tropical cyclones, and ET over the western North Pacific. The activities of the Asian THORPEX Committee were presented by Dr. T. Nakazawa. Over this region, emphasis has been placed on tropical cyclone track, the role of the Madden-Julian Oscillation in forcing episodes of large-scale deep convection and tropical cyclone formation, ET, and interannual variability in tropical cyclone landfall locations. As emphasized by the North American Committee report, the Asian Committee is also preparing for a combined observation and predictability impacts program during the summer of 2008. While the North American interests are primarily

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focused on ET and downstream impacts, the Asian Committee interest will be on tropicacyclone formation and track, with emphasis on the recurvature of tropical cyclones toward Japan.

l

r. J. McBride reported on the start of the Southern Hemisphere THORPEX Committee.

r. S. Jones provided a summary of the European THORPEX Committee and the

l ine

it

. Downstream impacts of ET

ollowing the reports on the overview of THORPEX, a more focused examination of the

his was followed by a discussion of the proposed THORPEX Pacific Asian Regional

. Predictability of the downstream impacts of ET

this session, Dr. P. Gauthier provided an overview of the linkages between data

DWhile there are many high-impact weather events over the Southern Hemisphere that have common factors to those in the Northern Hemisphere, some important differenceswere examined in the presentation. The goals of the Southern Hemisphere THORPEX committee parallel those of the overall THORPEX program. DTHORPEX Working Group on Predictability and Dynamical Processes (PDP). Contained in this Working Group are ten interest groups. One interest group wilexamine predictability of tropical cyclones and their ET. A second group will examthe downstream impacts associated with ET. Dr. Jones also presented the plans associated with the African Monsoon Multidisciplinary Analysis (AMMA) program asrelates to THORPEX and the PDP Working Group. b Fdownstream impacts associated was begun. Initially, an overview of the downstream impacts associated with ET was presented by Dr. P. Harr. Several cases were presented to illustrate the generation of a Rossby wave response downstream of an ET event over the western North Pacific. However, it was also noted that there is a large amount of case-to-case variability in downstream impacts. A large downstream wave response was generated during the ET of TY Nabi (Figure 3, top) while during the ET of TY Saola (Figure 3, bottom) now wave response occurred. It was noted that the specific mechanisms that impact the variability in wave response are not understood. TCampaign (T-PARC) and how it will address various aspects of ET over the western North Pacific, which include variability associated with downstream responses during the ET of tropical cyclones over the western North Pacific. Based on discussions of the proposed program and benefits to weather forecasts at a variety of time scales, it was decided that one recommendation of the Workshop would be to fully support the T-PARC program. c Indistribution, data assimilation, and forecast model performance with respect to downstream impacts. Although not strictly related to ET events, results associated with the downstream propagation of observation influence were presented. It was

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Figure 3. Height anomalies at 500 hPa for two times associated with the ET of (top) TY Nabi (top) and (bottom) TY Saola. demonstrated that forecasts of high-impact weather events over North America were related to the quality of the global analysis. Furthermore, analysis quality was severely impacted by instabilities that depend on flow characteristics. It was stressed that the ET of a tropical cyclone often impacts the instabilities related to analysis quality. The predictability associated with downstream impacts related to ET events was discussed in relation to the United Kingdom Meteorological Office (UKMO) was presented by Dr. T. Hewson. It was demonstrated that the error growth with forecast lead time increases during the fall season, which coincides with the climatological maximum in ET occurrences. Specific cases typified several error characteristics during ET events. In particular, forecasts of downstream events during ET suffer from a severe lack of consistency in forecast sequences. Because ET events occur over data sparse regions, are sensitive to initial conditions, and involve complex physical processes, they have severe impacts on operational forecast models. d. Diagnosis of downstream impacts due to ET. Several presentations focused on the diagnosis of downstream impacts due to ET via examination of the variability in ensemble prediction systems. In a presentation by Dr. P. Harr, the hypothesis that the increased variability among ensemble members downstream of an ET event is due to uncertainty in the forecast ET type was examined. A combined empirical orthogonal function (EOF) analysis and cluster analysis was employed to objectively identify a set of common forecast scenarios related to the ET of a tropical cyclone. As the time to the ET event decreases, the number of clusters decreases and confidence in the predictability of the ET increases.

Ex-TY Saola

Ex-TY Nabi

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D. Anwender applied the combined EOF and cluster analysis to a variety of ET events over the western North Pacific and the North Atlantic. It was demonstrated that none of the clusters representing possible ET scenarios in the ensemble prediction system of the European Center for Medium Range Weather Forecasts (ECMWF) contained the correct scenario until the forecast interval decreased to at least 72 h. Dr. S. Jones presented a new method for optimizing the region selection for singular vectors at the ECMWF that enhances the analysis associated with ET events over the subtropics and presents increased variability in the immediate areas of a tropical cyclone. It was stressed that it is not possible to track forecast continuity of individual ensemble members since perturbations are uncorrelated from one initialization to the next. e. Downstream impacts – modeling studies. The impact of the ET of Hurricane Katrina on the midlatitude flow patterns was examined by Dr. R McTaggart-Cowan. Although poleward movement of Hurricane Katrina did not result in a re-intensification as an extratropical cyclone, a significant impact on the midlatitude flow was caused by the anomalous warm pool that moved into the midlatitudes is association with the remnants of Katrina. While Katrina contributed to the magnitude of the warm pool and to its track into the midlatitudes, the source of the warm pool was found to far upstream of Katrina and related to s tropical cyclone over the eastern North Pacific. The persistent warm pool contributed to a large-scale blocking pattern over the midlatitudes, which is related to reduced predictability. The warm pool was subsequently tracked (Fig. 4) as it proceeded to propagate around the Northern Hemisphere.

Figure 4. Track (black line) from 0000 UTC 2 September to 0000 UTC 11 September 2005 of the persistent warm pool (potential temperature on the dynamic tropopause, K) associated with the poleward movement of Hurricane Katrina. Dr. S. Krichak discussed the forcing of a significant rain event over Israel that was associated with the interaction of a coherent tropopause disturbance and a precipitable water anomaly that was associated with Hurricane Olga. The evolution of this event was

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examined with respect to shifts in the Atlantic and Siberian anticyclones that contributed to moisture advection over the eastern Mediterranean Sea. The results of an idealized modeling study of the interactions between a tropical cyclone and midlatitude jet stream were presented by M. Riemer. Two types of scenarios were examined. The first case examined the interaction of poleward-moving tropical cyclone with a straight jet and the sensitivities associated with variations in the structure of the tropical cyclone and the midlatitude jet. While all cases resulted in some downstream impacts, the timing and magnitude of the downstream response varied with tropical cyclone size and jet intensity. For example, the downstream response associated with a small, weak tropical cyclone (Fig. 5a) began later and was weaker than the response associated with a larger and stronger tropical cyclone (Fig. 5b). Furthermore, the interaction between a large tropical cyclone tended to result in an anticyclonic lifecycle downstream development with a primary meridional orientation. When the interaction occurred with a stronger jet, the downstream development occurred faster and had a more zonal orientation.

A day 2

day 4

day 6

day 8

Figure 5. Time-longitude distribution associated winteraction between a straight midlatitude jet streamcyclone, and (b) large, strong tropical cyclone. Win A second set of experiments examined the interstream that contained baroclinic development. Rthat upper-level processes and tropical cycldevelopment of downstream waves. The largdefined by the character of the midlatitude flow tropical cyclone were only important within one wa Dr. S. Aberson presented some results of an Hurricane Ophelia as it began the ET process overadar data indicated a tilt in the vortex center that vheight. Because the NCEP Global Forecast Sysquite accurate, the impact of the dropwindsonde dHowever, the dropwindsonde data did impactGeophysical Fluid Dynamics Laboratory (GFDL) hu

18

B

ith the downstream impacts due to the

and (a) small, weak tropical d speeds (m s-1 ) are at 45oN.

action of a tropical cyclone and a jet esults of these experiments indicated one-jet interactions dominated the e-scale impacts were predominantly and variations in the structure of the velength of the ET location.

aircraft reconnaissance mission into r the western North Atlantic. Doppler aried from northeast to northwest with tem (GFS) forecasts of Ophelia were ata on the forecasts was not too great. the weakening of Ophelia in the rricane model.

CHAPTER 5

DIRECT IMPACTS OF EXTRATROPICAL TRANSITION The sessions on direct impacts of the ET of tropical cyclones was divided into two sections. Initially, the perspectives of operational forecast centers on the direct impacts of ET were discussed. Since there a representative from nearly every operational center that must forecast for ET conditions was present at the Workshop, a series of discussions lead to a comprehensive analysis of the primary operational concerns regarding ET. This provided for immediate input as recommendations related to improving the ability forecast the ET of tropical cyclones. Secondly, observations and diagnosis of direct impacts were discussed. These revolved around specific events and analysis of relative contributions from physical mechanisms regarding a variety of tropical cyclone and midlatitude circulation characteristics. a) Operational aspects Dr. J. Beven provided a summary of the operational aspects associated with forecasting ET at the U. S. National Hurricane Center (NHC). Overall, distribution of timing error bias associated with all forecasts of ET is skewed toward a positive time bias (Fig. 6) with an average timing error of 14.5 h. Specific operational issues involve forecasts associated with the cyclone type. This is important because forecasts of ET are related to the initiation of the ET process and no verification is done after the tropical cyclone has been declared as extratropical. Forecast errors associated with ET are related to timing between the tropical cyclone and a midlatitude trough. It would be useful to have a climate and persistence (CLIPER) model that was specifically applicable for ET forecasts. Then, a baseline for predictive skill could be established.

Time Bias Histogram

0

5

10

15

20

25

30

35

-69

-63

-57

-51

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-39

-33

-27

-21

-15 -9 -3 3 9 15 21 27 33 39 45 51 57 63 69

Mor

e

Time Bin (hr)

Freq

uenc

y

Frequency

Figure 6. Histogram of the time bias associated with all forecasts of ET by the U. S. National Hurricane Center. Dr. Beven stressed that the western North Atlantic was unique in that tropical cyclones often continued to intensify via typical processes related to tropical cyclone intensification following recurvature. This is partly due to the presence of the Gulf Stream and its impact on maintenance of deep convection to allow a delay in the effects

19

of increased vertical wind shear after recurvature. Therefore, there could be large consequences to forecasting the start of ET prematurely. This is a likely cause of the positive time bias and mean error. J. Callaghan presented operational issues with respect to forecasting for ET events over the western South Pacific. In particular, a variety of tropical and subtropical circulations undergo ET over this region. The importance of the forcing by warm advection at 700 hPa and 200 hPa was stressed as important mechanisms in the forcing of extreme precipitation events over eastern Australia. Dr. N. Kitabatake presented issues associated with forecasts of ET in the vicinity of Japan. Major concerns were associated with the difficulty in identifying a circulation center such that maintaining a coherent track estimate is difficult. This related to identification of areas in which rain and/or wind will occur. It is also difficult to convey to the public that they may be in an area where rain will be severe but not wind. It was stressed that even with a well-distributed and comprehensive data network; it is still difficult to classify the circulations as they begin the ET process. Finally, there are critical issues associated with the timing and location of the interactions between the tropical cyclone and the midlatitude baroclinic zone. These factors impact where heavy precipitation will occur, which is often located far from the decaying tropical cyclone center. Impacts due to forecasts of ET over Atlantic Canada were presented by Dr. S. Miller for a case study of the ET of Hurricane Karen (2001). In this case, there were in situ observations from the Environment Canada Convair aircraft. The data revealed that the boundary layer was very stable with an area of tropical storm force winds immediately above the boundary layer. The remnant warm core was readily identifiable. A suite of numerical experiments were conducted to examine the improvements that can be realized from improved initial conditions based on the in situ data. R. Das presented the forecasting perspective for the south West Pacific region near New Zealand. On average, one to two tropical cyclones impact the region around New Zealand each year. A significant ET event is likely every 20 years. There is a strong relationship to the El Nino/Southern Oscillation (ENSO) cycle in that major events tend to occur during neutral years. The impacts to New Zealand vary based on the track of the tropical cyclone. Typically, tropical cyclones moving west of New Zealand are fast moving and bring strong winds to New Zealand. Furthermore, a trapped fetch that is common with these systems can cause severe ocean swells in these conditions. A tropical cyclone that moves east of New Zealand moves slowly and brings long periods of heavy rains. Although numerical forecasts of ET are improving, the discrepancy among model members causes confidence to be low in many cases. A. Charlot presented the operational perspectives associated with ET over the western Indian Ocean. Over this region, it was noted that tropical cyclones may retain tropical characteristics to 40oS. This often presents difficult scenarios with respect to timing between of the interaction between the tropical cyclone and the midlatitude circulation into which it is moving. In particular, there is a lack of objective guidance as to decide when a system has begun the ET process. While the cyclone phase space has some merit in this regard, it is dependent on the representation of the tropical cyclone and midlatitude circulation in a numerical model.

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The session on operational perspectives of direct impacts due to ET was concluded by a plenary session to address the question of what is known and what is not known. Overall, it was agreed that the primary known factor is really only climatology. The frequency, spatial distributions, and typical synoptic-scale patterns are all identifiable in climatological data. However, the variability is extremely large and this constitutes the source of what is not known. Typical questions revolve around the type of ET that will occur (i.e., capture, transformation, re-intensification), the timing of the initiation of ET, the duration of ET, the track during ET, and the predominant weather and ocean conditions during the ET. There was considerable debate as to the need for objective classification of storm type. However, it was stressed that it is often immaterial if the system is declared tropical, hybrid, or extratropical since damaging winds or heavy rains apply to all these classifications. It is also important to recognize whether a decaying tropical cyclone will dissipate, be absorbed by a midlatitude cyclone, or re-intensify and absorb a midlatitude cyclone. The importance of accurate track forecasts during ET was emphasized. Questions centered on whether the operational numerical prediction systems exhibited similar skill with forecasts of cyclones that resulted from ET as typical midlatitude cyclones. Important questions remain as to the role of the ocean during ET. As the primary energy mechanism changes from baroclinic processes from latent heat release, does energy from the ocean continue to be a primary forcing mechanism? Also, the generation of extreme wave conditions was stated to be a serious forecast problem. Specific cases (i.e., the ET of Hurricane Maria (2005), the ET of Hurricane Philippe (2005)) were cited by NHC and UKMO as exhibiting particular problems related to forecasting direct and indirect impacts of ET. In the case of Maria, the timing errors associated with forecasts of ET were larger than 24 h. In the case of Philippe, the ET and downstream impacts were largely over forecast. Therefore, a tremendous amount of variability exists in the mechanisms associated with ET and the ability to forecast ET. Furthermore, the variability in processes, timing, and interactions among tropical and midlatitude factors represent the primary unknowns in being able to increase the forecast accuracy with respect to ET. b) Diagnostics Dr. Y. Duan presented the analysis of the landfall of TY Talim (2005) and the extreme rainfall that occurred over inland provinces of China. The analysis examined the role of a secondary circulation center in which there was also interaction with topographic features that acted to concentrate the distribution of precipitation. The development of the secondary circulation in relation to the remnants of Talim were examined via a vorticity budget that indicated that horizontal advection of vorticity associated with the 500 hPa trough was the primary mechanism responsible for development of the secondary circulations. The importance of variation in tropical cyclone intensity at landfall was presented by Dr. T. Peng. In this analysis, the importances of the general atmospheric conditions at landfall were stressed in relation to the characteristics of the tropical cyclone itself. It was found that the three dominant factors impacting intensity change at landfall involved

21

the intensity of the tropical cyclone, the stability of the upper atmosphere and the total column distribution of moisture. Dr. L. Ying presented a study of the importance of upper-level troughs on the ET of TY Winnie (1997). A numerical model was used to examine the sensitivity of the ET process to a variety of upper-level trough characteristics that included the strength or the trough and the position of the trough relative to the decaying tropical cyclone. Results indicated that trough strength significantly impacted the ET process by accelerating the rate at which an upper-level potential vorticity anomaly would extend downward to impact low-level re-intensification of the tropical cyclone as an extratropical cyclone. Dr. H Ritchie presented a series of studies that examined high-resolution simulations of several ET events that impacted the Atlantic provinces of eastern Canada. Their results emphasized the importance of synthetic vortex insertion and the impact on initial conditions as being important factors in determining the ability of high-resolution numerical models to properly model the complex interactions between the decaying tropical cyclone and the midlatitude circulation into which it is moving. Initialization of the model with varying initial vortex specifications provided initial conditions for generation of ensemble predictions. The variability among ensemble members was used to examine the sensitivity to initial vortex specification. Simulations of Hurricane Katrina and Hurricane Ophelia were also presented by Dr. H. Ritchie to emphasize the role of sea-surface temperature distribution in the simulations of Katrina and the impact of dropwindsonde data on the simulations of Ophelia. Dr. E. Ritchie presented a study that identifies factors that will discriminate among cases that undergo re-intensification during ET or decay. Simulations from a high-resolution mesoscale model were used to define a set of physical parameters that might discriminate among possible results of the ET process. Signal processing pattern recognition techniques are then applied to the parameter set to provide an indication of possible re-intensification or decay. The technique is dependent upon an objective identification of the ET time. A series of presentations by Dr. R. Hart addressed several spatial and temporal factors associated with ET. In one presentation, Dr. Hart, examined factors that may indicate over time periods of a week to months whether there was an increased probability of recurving tropical cyclones that would lead to an increased number of ET events. Re-analysis data were utilized to examine the roles of various global-scale circulations on the tropical cyclone track characteristics. While several factors (e.g., ENSO) significantly impact the number of tropical cyclones that occur over the North Atlantic, there was less significance associated with factors that define the possibility of ET over the North Atlantic. Also, Dr. Hart examined the location of formation for storms that eventually impacted Europe, Canada, and the northeast United States. It was found that the variability in storm locations increased as impacts changed from the northeast United States, to Canada, to Europe. In a second presentation, Dr. Hart presented a composite analysis of the lifecycle of ET events over the North Atlantic. The purpose was to examine factors that lead to re-intensification as an extratropical cyclone rather than decay of the original tropical cyclone. It was concluded that the process was extremely sensitive to the timing of the interactions between the decaying tropical cyclone and the midlatitude circulation. Given the degree of sensitivity and the current skill in prediction of the timing of trough and

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tropical cyclone interactions at a range of 3 – 5 days, the currently observed decrease in predictive skill during ET is clear. Dr. J. Gyakum analyzed a set of tropical cyclones and ET events that affected Atlantic Canada since 1979. Based on a framework of quasigeostrophic dynamics and a potential vorticity perspective the cases were partitioned based on whether they re-intensified or decayed. Based on this partitioning, the variability in precipitation fields was also examined.

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CHAPTER 6

RECOMMENDATIONS

a) Introduction Prior to presentation of recommendations for future activities related to the ET of tropical cyclone, Prof. R. L. Elsberry presented a summary of the First International Workshop on Tropical Cyclone Landfall Processes and how ET was related to the recommendations that came from that meeting. The Workshop on Landfall Processes recommended four demonstration projects that include an Intercomparison of high-resolution model simulations, a forecast demonstration project, an Asian THORPEX project, and an ET project in conjunction with THORPEX. Discussion during IWET III that were centered around the proposed THORPEX Pacific Asian Regional Campaign (T-PARC) which is being proposed as an international project that involves the Asian and North American THORPEX communities, advanced the fourth project from the Workshop on Landfall Processes. . As a part of T-PARC, Observations of the structure changes during the transformation stage of ET and the conditions leading to re-intensification as an extratropical cyclone will benefit forecasters and lead to better understanding. Furthermore, modeling and ensemble predictions will improve forecasts of the downstream impacts. Although the lead agency of T-PARC will be THORPEX, the objectives of WMO/TMPR will be addressed via this program. b) Recommendations The following recommendations were compiled based on presentations and discussions during the IWET III sessions. A plenary session was held to introduce, discuss, and refine each recommendation. Recommendations are placed into categories similar to that from IWET II (Chapter 3), with the addition of downstream impacts. The primary issues associated in each category are summarized. Recommendations that address the issues are defined. c) Downstream impacts ISSUE: It is clear that ET events are related to decreases in forecast accuracy downstream of the ET event. Furthermore, the downstream impacts are extremely sensitive to the temporal and spatial interactions among a set of physical mechanisms. To address, the issue of downstream predictability, the T-PARC program includes a number of science objectives that pertain to ET. These address linkages between direct impacts of ET and the predictability of downstream high-impact weather events. RECOMMENDATIONS: It is recommended that WMO/CAS/TMPR facilitate participation from a variety of research and academic institutions and operational centers in T-PARC. Specifically, it is recommended that support to T-PARC goals be provided as input by forecasters and researchers that have responsibilities and interests in the problem of ET. This support should be provided in participation of the role(s) of data assimilation systems and their components that impact predictability, satellite data and the validation of satellite data, and data impacts on the growth of errors numerical model

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forecast products. Finally, participation by the ET community in T-PARC experimental design is highly recommended. It is recommended that a significant effort be place in identification of the primary mechanisms that link ET events to reduced predictability over regional and hemispheric scales. This includes identification of relative contributions to decreased predictability by midlatitude characteristics, tropical characteristics, and structural characteristics associated with the decaying tropical cyclone. The use of high-resolution models to examine physical processes is recommended. The use of ensemble prediction systems should be expanded to identify predictability associated with direct and indirect impacts of ET. It is recommended that efforts into diagnostic analysis of important components and mechanism associated with the ET of tropical cyclones be expanded to help guide the T-PARC design and refine significant scientific hypotheses. d) Tropical cyclone characteristics 1. Track ISSUES: The timing of recurvature and acceleration of a decaying tropical cyclone into the midlatitudes remains a major issue with respect to the timing and character of the ET process. Although cross-track errors are not typically large following recurvature, along-track errors can be very large. A slight displacement of the decaying tropical cyclone along the track will result in a significant change in direct and downstream impacts. Complicated factors arise as most ET cases involve two or more surface low-pressure centers due to the decaying tropical cyclone and the active midlatitude baroclinic zone. RECOMMENDATIONS: It is highly recommended that effective methods for examining and conveying the uncertainties associated with the highly variable interactions between the tropical cyclone and midlatitude circulation to forecasters. It is recommended that a goal of the THORPEX Interactive Grand Global Ensemble (TIGGE) project be t o work with forecasters to develop relevant guidance products, tools, and techniques for improvement in the forecast and warning programs associated with ET. During field campaigns, TIGGE data should be made available in real time to forecasters and researchers involved in the campaign. It is recommended that production of an internationally consistent database of tropical cyclone and ET phases be pursued. A consistent approach, which may be based on the cyclone phase space, should be applied to classify structural characteristics as input to this database. Use of reanalysis datasets should be encouraged in construction of this database. 2. Intensity ISSUES: Without the availability of in situ observations, the primary techniques available for estimating current intensity of a tropical cyclone are based on satellite imagery. These techniques are not well suited for ET cases. Many techniques base intensity estimates on the degree of symmetry in cloud patterns. While the distribution of clouds becomes quite asymmetric during ET, the wind speeds remain high. Therefore, standard satellite-based techniques often underestimate the intensity of the decaying tropical cyclone during ET.

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RECOMMENDATIONS: It is recommended that techniques be developed that allow determination of tropical cyclone intensity during ET. New datasets such as may be compiled from satellite archives and field programs such as T-PARC should be used to develop satellite-based tools for assessment of intensity during ET. There should be strong collaborations among operational forecast centers, and research scientists to develop techniques for intensity estimation. It is recommended that decay rates of tropical cyclone moving over cooler sea-surface temperatures and increased vertical wind shear be quantified. A climatology of ET events and their impacts could be used in an analog approach to define extreme conditions. It is recommended that techniques be developed to improve prediction of precipitation patterns and quantities related to ET. Important factors that govern the distribution and amount of precipitation must be identified and understood. e) Numerical weather prediction ISSUES: Accuracy of forecasts of ET events from operational numerical prediction models continues to be lower than overall forecast accuracy. RECOMMENDATIONS: It is recommended that decreased forecast accuracy be examined in relation to such factors as data quality and distribution, initial condition errors, and physical parameterizations, tropical cyclone characteristics, and midlatitude characteristics. The impact and benefit of synthetic vortex insertion or bogus observations in global and limited area models should be identified. Variability in model forecast quality should be identified as related to a spectrum of techniques used to initialize tropical circulations during ET in a numerical model. The utility of targeted observations and advanced adaptive data assimilation strategies that consider dynamical balance and flow dependence should be investigated with respect to improvements in initial conditions for ET events in numerical models. It is recommended that socio-economic impacts of ET be quantified as a justification for expansion of reconnaissance programs to provide increased data coverage in ET events. A comprehensive and systematic set of studies that relate the sensitivity of ET impacts to environment and tropical cyclone characteristics such that these impacts may be assessed with respect to strengths and weaknesses of operational numerical models. This includes increased understanding of important physical processes and development of parameterizations related to ET.

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Appendix A

AGENDA

Monday, 5 December Time Activity PPT Talks1130-1230 Lunch THORPEX - J. Abraham, Chair

1300-1330 Opening ceremony and workshop introduction L. Chen, G. Foley, E. Manaenkova

1330-1400 IWET-II: Summary and Recommendations J. Abraham 1400-1500 THORPEX Overview D. Burridge, M. Shapiro 1500-1530 Afternoon tea THORPEX cont'd - J. Abraham

1530-1700 Regional THORPEX Updates D. Parsons, P. Gauthier, T. Nakazawa, M, McBride, S. Jones

1700-1730 Downstream Impacts of ET: Overview P. Harr also AMMA S. Jones Evening Icebreaker

Tuesday, 6 December THORPEX cont'd - J. Abraham (Chair)

0830-1000 Discussion: Pacific Campaign 2008

D. Parsons, C. Velden, T. Nakazawa, P. Harr

1000-1030 Morning tea

Predictability of Downstream Impacts - S. Jones (Chair 1030-1100

A UK Met Office perspective on the influences of extra-tropical transition on operational forecasts T. Hewson

1100-1130 Canadian Meteorological Centre P. Gauthier

1130-1200

General Discussion on Operational Prediction of Downstream Impacts S. Jones

1200-1330 Lunch

Downstream Impacts - R. Elsberry (Chair)

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1330-1400

Predictability Associated with the Downstream Impacts of the Extratropical Transition of Tropical Cyclones: Methodology

P. Harr

1400-1430

Predictability Associated with the Downstream Impacts of the Extratropical Transition of Tropical Cyclones: Ensemble cases from 2005

D. Anwender

1430-1500

Predictability Associated with the Downstream Impacts of the Extratropical Transition of Tropical Cyclones: Ensemble sensitivity to initial perturbations

S. Jones

1500-1530 Afternoon tea

Downstream Impacts: modeling studies - E. Ritchie (Chair)

1530-1600 The Impact of Hurricane Katrina on the midlatitude flow R. McTagart-Cowan

1600-1630

Dynamic Tropopause Effects of a Dec. 2001Atlantic-Mediterranean Teleconnection Episode Initiated by Extratropical Transition of Hurricane Olga

S. Krichak

1630-1700

The impact of extratropical transition on the downstream flow: an idealized modeling study M. Riemer

1700-1730

The 2005 NOAA Hurricane Field Program: Observations of the Extratropical Transition of Hurricane Ophelia and the Impact of Tropical Convection in the Extratropics.

S. Aberson

also WGNE M. Miller also Irene A.Charlat

Wednesday, 7 December

Direct Impacts of ET: Operational perspectives - C. Velden (Chair)

0900-0930 NHC Perspective J. Beven

0930-1000

Extra-tropical Transition and the continuum between extra-tropical cyclones and tropical cyclones J. Callaghan

1000-1030 Morning tea

Direct Impacts of ET: Operational perspectives cont'd - C. Velden

1030-1100

Extratropical Transition of the Tropical Cyclones that Made Landfall on Japan in 2004: Overview and Case Studies

N. Kitabatake

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1100-1130

The Extratropical Transition Of Hurricane Karen(2001): Data And Modeling Studies S. Miller

1130-1200 New Zealand Perspective R. Das

1200-1330 Lunch (provided)

LAB - C. Velden, A. Burton 1330-1500

Forecasting ET: What we know and what we don't know

T. Hewson, J. Beven, S. Miller, A. Burton

1500-1530 Afternoon tea

LAB 1530-1630 Cyclone Phase Space Clusters and Composites B. Hart , J. Evans

1630-1700 La Reunion and ETT A.Charlat

1700-1730 ET of TY Talim Yihong DUAN

Thursday, 8 December

Direct Impacts of ET - G. Gyakum, J. Evans (Chairs) 0830-0900 Canada Modeling Results H. Ritchie

0900-0930

Numerical Modeling of Atlantic Hurricanes Moving into the Middle Latitudes H. Ritchie

0930-1000

Variation of Landfalling TC Intensity and Its Relationship with Structural Characteristics of the Environmental Fields

T. Peng, Z. Cheng

1000-1030 Morning tea

Direct Impacts of ET cont'd - G. Gyakum, J. Evans (Chairs)

1030-1100

Phasing Between the Upper-level Trough and Tropical Cyclone During Simulated Extratropical Transition E. Ritchie

1100-1130

Simulation of Impacts of Midlatitude Upper-level Troughs on the ET of Typhoon Winnie Y. Li

1130-1200

Short and long-term indicators of enhanced Atlantic tropical cyclone threat at higher Latitudes R. Hart

1200-1330

Lunch

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Direct Impacts of ET cont'd - G. Gyakum, J. Evans (Chairs)

1330-1400

Study on the Interaction between Westerly Trough and Typhoon in Western North Pacific L. Chen, Y. Li

1400-1430

Dynamical Structures And Precipitation Distributions Of Transitioning Tropical Cyclones That Affect Canada J. Gyakum

1430-1500

Towards a better understanding of and ability to forecast the wind field expansion during the extratropical transition process R. Hart

1500-1530 Afternoon tea

WMO/IWTC-VI - G. Foley (Chair) 1530-1630 Macau and IWTC-VI R. Elsberry,

J. C. Chan 1630-1730 Plenary session: Recommendations and actions arising G. Foley, J.

Abraham

Friday, 9 December Activity Venue 0900-1000 Final Summaries: Closing Ceremony Observation City

Tour of Bureau of Meteorology, Western Australia Regional Office.

Perth, Australia

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Appendix B

Registrants

Registrants are listed alphabetically

Name Organization Dr. S. Aberson NOAA/AOML/Hurricane Research Division Dr. J. Abraham Enviroment Canada Ms. D. Anwender Universitat Karlsruhe Mr. J. Beven National Hurricane Centre, Miami Mr. D. Burridge WMO Mr. A. Burton Bureau of Meteorology, Australia Mr. J. Callaghan Bureau of Meteorology, Australia Mr. J. Chan City University of Hong Kong Ms. A. Charlat-Abeille METEO-France, RSMC of La Reunion Prof. L. Chen Chinese Academy of Meteorological Sciences Mr. J. Courtney Bureau of Meteorology, Australia Mr. V. Raveen Das Meteorological Service of New Zealand Dr. Duan China Mr. D. Duncalf Metocean Engineers Pty Ltd Mr. G. Elliott Bureau of Meteorology, Australia Prof. R. Elsberry Naval Postgraduate School, Monterey Prof. J. Evans The Pennsylvania State University Mr. G. Foley Bureau of Meteorology, Australia Dr. P. Gauthier Meteoroligal Service of Canada Mr. J. Gyakum Canada Mr. B. Hanstrum Bureau of Meteorology, Australia Dr. P. Harr Naval Postgraduate School, Monterey Dr. R. Hart Florida State University Mr. T. Hewson UK Meteorological Office Prof. S. Jones Universitat Karlsruhe Ms. N. Kitabatake Japan Meteorological Agency Dr. S. Krichak Tel Aviv University Ms. M. Lajoie Canadian Meteorological Centre Dr. Lei WMO Mr. Y. Li Chinese Academy of Meteorological Sciences

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Ms. E. Manaenkova WMO Dr. J. McBride Bureau of Meteorology, Australia Mr. M. McCormack Australia Mr. M. Miller ECMWF, UK Mr. S. Miller Environment Canada/ Canadian Hurricane Centre Mr. T. Nakazawa Japan Meteorological Agency Mr. S. Noreika Metocean Engineers Pty Ltd Mr. D. Parsons National Center for Atmospheric Research Mrs. L. Paterson Bureau of Meteorology, Australia Mr. T. Peng Guangzhou Central Meteorological Observatory Mr. G. Reader Bureau of Meteorology, Australia Mr. M. Riemer Research Center Karlsruhe Mr. H. Ritchie Canada Prof. E. Ritchie-Tyo University of New Mexico Mr. A. Sharp Bureau of Meteorology, Australia Mr. M. Shapiro NOAA Dr. Tunegovelets Russia Mr. C. Velden University of Wisconsin Mr. E. Zannou South Africa

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