Weekly Climate Update August 26 th , 2008

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Weekly Climate Update August 26Weekly Climate Update August 26thth, 2008, 2008

The July 2008 tropical season was the third most active July on record. Only The July 2008 tropical season was the third most active July on record. Only 1916 and 2005 were more active (ACE). According to NOAA, the explanation for 1916 and 2005 were more active (ACE). According to NOAA, the explanation for this high activity has been the lingering La Nina.this high activity has been the lingering La Nina.While La Niña has officially transitioned to a neutral phase (based on Nino3.4), While La Niña has officially transitioned to a neutral phase (based on Nino3.4), many aspects of the atmospheric circulation and pattern of tropical convection many aspects of the atmospheric circulation and pattern of tropical convection reflect a lingering La Niña signal in the atmosphere “Some of these lingering effects reflect a lingering La Niña signal in the atmosphere “Some of these lingering effects include reduced wind shear, weaker trade winds, an active West African monsoon include reduced wind shear, weaker trade winds, an active West African monsoon system, the winds coming off of Africa and warmer-than-average water in the system, the winds coming off of Africa and warmer-than-average water in the Atlantic Ocean.’Atlantic Ocean.’ said Gerry Bell, Ph.D., lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center. The strong cold phaseThe strong cold phase of PDO favors La Nina PDO favors La Nina type conditions over El Nino conditions on inter-annual to decadal time scales and type conditions over El Nino conditions on inter-annual to decadal time scales and likely contributed to the active season so far. likely contributed to the active season so far.

(http://www.cpc.noaa.gov/products/outlooks/hurricane.shtml ). (http://www.cpc.noaa.gov/products/outlooks/hurricane.shtml ). In addition to the La Nina effects, the Atlantic sea surface temperature anomalies In addition to the La Nina effects, the Atlantic sea surface temperature anomalies in the Main Development Region for tropical systems have also increased in the Main Development Region for tropical systems have also increased somewhat since early July. Consistent with the temperature increase and the somewhat since early July. Consistent with the temperature increase and the lingering La Nina conditions both NOAA and CSU have increased their August lingering La Nina conditions both NOAA and CSU have increased their August prediction of tropical storm activity. This should not be surprising since 10 out of prediction of tropical storm activity. This should not be surprising since 10 out of 13 years beginning in 1995 (the year the AMO returned to its warm phase) have 13 years beginning in 1995 (the year the AMO returned to its warm phase) have had an above normal number of tropical storms. had an above normal number of tropical storms.

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The CSU August forecasts include 17 tropical storms, 9 hurricanes and The CSU August forecasts include 17 tropical storms, 9 hurricanes and 5 intense hurricanes. NOAA predictions are for 14-18 tropical storms, 7-5 intense hurricanes. NOAA predictions are for 14-18 tropical storms, 7-10 hurricanes and 3-6 major hurricanes. Dr. Gray has modified his 4 10 hurricanes and 3-6 major hurricanes. Dr. Gray has modified his 4 analog years (1926, 1961, 1996, 2000) to include 1926 and 1996. The analog years (1926, 1961, 1996, 2000) to include 1926 and 1996. The 1926 tropical season includes the great Miami Hurricane.1926 tropical season includes the great Miami Hurricane.The North Atlantic Oscillation (NAO) index has been trending The North Atlantic Oscillation (NAO) index has been trending downward and is currently negative. A negative NAO index is associated downward and is currently negative. A negative NAO index is associated with a greater chance of hurricane landfalls along the Gulf Coast of the with a greater chance of hurricane landfalls along the Gulf Coast of the U.S. and Florida [Elsner and Bossak, 2004]. The NAO has specific U.S. and Florida [Elsner and Bossak, 2004]. The NAO has specific effects upon the Bermuda high pressure system in the Atlantic Ocean.effects upon the Bermuda high pressure system in the Atlantic Ocean. A A negative NAO allows for a weaker more westward centered Bermuda negative NAO allows for a weaker more westward centered Bermuda High, which acts to steer North Atlantic hurricanes toward the southern High, which acts to steer North Atlantic hurricanes toward the southern United States rather than re-curving toward the open North Atlantic United States rather than re-curving toward the open North Atlantic [Slide 25]. [Slide 25].

http://garnet.acns.fsu.edu/~jelsner/PDF/Research/ElsnerLiuKocher2000.pdf Summary of current global ocean-climate conditions can be found at Summary of current global ocean-climate conditions can be found at the following link: the following link: http://ioc3.unesco.org/oopc/state_of_the_ocean/all/ The CPC official climate outlook indicates an increased chance for The CPC official climate outlook indicates an increased chance for above normal rainfall for the September through November climate above normal rainfall for the September through November climate window.window.

(Continue from previous Slide)

Slide2004-2008 monthly tropical Atlantic sea surface temperature anomalies………………….............… 3

Sea Surface Temperatures Anomalies in the tropical storm Main Development Region (MDR)...… 42007-2008 La Nina (Nino 3.4 index) compared with other ENSO events during the past several year 5The evolution of sea surface temperature anomalies (SSTA) in the east-central equatorial Pacific ocean………………………………………………………………………………………………...... 6 The equatorial Pacific Ocean NINO Indices ………......................……………….……………….… 7Trend in the subsurface anomalies..………………………….….……………………………....……. 8Current Global Sea surface temperature anomalies………….……………………….………...…….. 9The Climate Forecasting System (CFS) sea temperature anomalies predicted.…………….……….... 10North Atlantic Oscillation ……………………………….…………..…..………...……………….…. 11Seasonal Probability of each phase of ENSO……………………...…………………………………. 12The Official CPC Climate Outlook……………………….……………………................................... 13Lake Okeechobee August 1st PA Percentiles…………………………………………………………. 14Lake Okeechobee August 1st PA with Neutral ENSO……………….………………………………... 15Lake Okeechobee August 1st Neutral ENSO/AMO warm phase sub samplings……………………... 16 Backup Slides

Table of ContentsTable of Contents

Evolution of Tropical Atlantic SST IndicesEvolution of Tropical Atlantic SST Indices

- Tropical North Atlantic SST has been steadily

increasing since April.

- Meridional Gradient SST (TNA-TSA) is

approaching zero in July.

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(0C)

MDRMDR MDR MDR MDR

Sea Surface Temperatures Anomalies in the Tropical Storm

Main Development Region (MDR)

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NINO 3.4NINO 3.4

El Nino-Southern Oscillation IndexEl Nino-Southern Oscillation Index

2007-2008 La Nina compared with other ENSO events since 1981.

ENSO is currently in neutral conditions.http://ioc3.unesco.org/oopc/state_of_the_ocean/sur/pac/nino3.4.php

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Recent Evolution of Equatorial Pacific SST Departures (Recent Evolution of Equatorial Pacific SST Departures (o o C)C)Climate Prediction Center Climate Prediction Center

El Nino-Southern Oscillation Weekly UpdateEl Nino-Southern Oscillation Weekly Update

Longitude

Time

Nino 3.4 continues slow warming

August 2007

November2007

July2008

NINO3.4

Since February 2008, negative sea surface temperature anomalies have weakened over the central and east-central equatorial Pacific Ocean.

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NiNiño Region SST Departures (ño Region SST Departures (o o C) Recent EvolutionC) Recent Evolution Climate Prediction Center Climate Prediction Center

El Nino-Southern Oscillation Weekly UpdateEl Nino-Southern Oscillation Weekly Update

The latest weekly SST departures are:

Niño 4 -0.4ºC

Niño 3.4 0.0ºC

Niño 3 0.5ºC

Niño 1+2 0.4ºC

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Longitude

Sub-Surface Temperature Departures (o C) in the Equatorial Pacific Ocean (August 18th , 2008)

Bureau of Meteorology Research Centre

May

Jun

Jul

At this time neutral conditions are in place. These conditions are likely to persist into next dry season. However, El Nino or La Nina conditions can be ruled out for the next dry season. A cool subsurface anomalies has recently appeared in the equatorial Pacific and needs to be monitored.

Aug

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Latest Weekly Sea Surface Temperature AnomalyLatest Weekly Sea Surface Temperature AnomalyNational Climate Data CenterNational Climate Data Center

The Atlantic Main hurricane development region has experienced warming the past several week.

AB

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Equatorial Pacific SST and Subsurface Temperature Anomaly ForecastEquatorial Pacific SST and Subsurface Temperature Anomaly Forecast NCEPNCEP Climate Forecast System Issued August 25 Climate Forecast System Issued August 25thth 2008 2008

The CFS ensemble mean (heavy blue line) predicts La Niña most likely will be in neutral conditions for

the remainder of the tropical season.

The CFS ENSO ensemble forecast has had a significant upward shift during recent weeks.

Regions illustrated above are the Indian, Pacific, and Atlantic tropical oceans subsurface temperature anomalies.

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IRI Probabilistic ENSO Forecasts for the NINO 3.4 Region

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North Atlantic Oscillation

The IRI ENSO model summary supports the cfs prediction that ENSO most likely to remain in the neutral phase.

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CPC Seasonal Rainfall OutlookCPC Seasonal Rainfall Outlook

September- NovemberSeptember- November December-FebruaryDecember-February

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August 1st Position AnalysisAugust 1st Position Analysis

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August 1August 1stst ENSO neutral years Position Analysis ENSO neutral years Position Analysis

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August 1August 1stst Position Analysis Position Analysis

ENSO Neutral/AMO Warm sub samplingENSO Neutral/AMO Warm sub sampling

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Backup Slides with additional support material

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PDO cold phase equals less El Nino more La Nina and drier dry seasons

http://www.americanthinker.com/blog/2008/04/nasa_confirms_natural_climate.html

ENSOENSO

PDOPDO

La NinaLa Nina predominates predominates when PDO is in negative when PDO is in negative phase phase

El NinoEl Nino predominates predominates when PDO is in positive when PDO is in positive phase phase

Currently transitioning

to cold phase of PDO

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AO (or NAO) – North AtlanticAO (or NAO) – North Atlantic

• Larson et al. (2006, J. Climate)– The AO (and/or NAO) has a strong

influence on the intraseasonal and interannual variability of NA TC activity.“During La Niña (El Niño) conditions, atmospheric circulation appears more (less) conductive to TC activity in the main developing region [MDR] during AO-positive (negative) conditions than during AO negative (positive) ones.”

– An enhanced (decreased) TC activity during the positive (negative) phase of the AO. During the positive phase of the AO,

• The subtropical ridge in the NA is enhanced.

• The westerly wind shear weakens over the MDR.

• The tropical easterly jet intensifies over Africa.

→ provide favorable conditions for TC development.

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Composites associated strongest AMM (+) and AMM (-)

Tropical cyclo-genesis points for the five strongest and five weakest AMM years, superimposed on composites of SST (shaded) and shear (contours) anomalies. Crosses show the genesis points for all storms that reached tropical storm strength. Storms that reached “major hurricane” strength (maximum sustained surface wind speed > 49 m s-1) also have a circle around their genesis point. Solid (dashed) shear contours denote positive (negative) values. The contour interval is 0.25 m s-1 and the zero-contour has been omitted. Shear was calculated every 6 h as the amplitude of the vector difference between the layer-mean winds in the 300–150 hPa and 925–700 hPa layers, and means were formed around the hurricane season from monthly means.

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Moisture Percentile for July 24th , 2008

Land Surface Hydrology Research Group

Princeton Universityhttp://hydrology.princeton.edu/~luo/research/FORECAST/current.php

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The drought analysis is based on comparing the current soil moisture against the 54-yr retrospective climatology. The climatology is developed separately for each grid cell (> 55,000 cells in the USA) in the form of a pdf. The original drought analysis (Sheffield et al. 2004) fitted beta distributions to the soil moisture data. In this update a empirical distributions based directly on the data is applied. The plots shows the percentile of current soil moisture with respect to the 54-yr climatology defined as all values in a 49-day sampling window centered at 2008/07/24

(Discussion Related to previous Slide)

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Correlation between RF and Atlantic Meridional Mode and Atlantic Multidecadal OscillationCorrelation between RF and Atlantic Meridional Mode and Atlantic Multidecadal Oscillation

AMM AMO

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