Synoptic environments associated with predecessor rain events in advance of landfalling tropical cyclones Benjamin J. Moore, Lance F. Bosart, and Daniel Keyser Department of Atmospheric and Environmental Sciences, University at Albany/SUNY, Albany, NY 12222 Michael L. Jurewicz, Sr. NOAA/NWS, Binghamton, NY Northeast Regional Operational Workshop XI, Albany, NY 5 Nov 2009
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Benjamin J. Moore, Lance F. Bosart , and Daniel Keyser
Synoptic environments associated with predecessor rain events in advance of landfalling tropical cyclones. Benjamin J. Moore, Lance F. Bosart , and Daniel Keyser Department of Atmospheric and Environmental Sciences, University at Albany/SUNY, Albany, NY 12222 Michael L. Jurewicz , Sr. - PowerPoint PPT Presentation
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Synoptic environments associated with predecessor rain events in advance of
landfalling tropical cyclones
Benjamin J. Moore, Lance F. Bosart, and Daniel KeyserDepartment of Atmospheric and Environmental Sciences, University at
Albany/SUNY, Albany, NY 12222
Michael L. Jurewicz, Sr.NOAA/NWS, Binghamton, NY
Northeast Regional Operational Workshop XI, Albany, NY
5 Nov 2009
NOAA/CSTAR Grant NA07NWS4680001
Outline
• Motivation• Definition of a PRE• Data and methodology• TC-relative composite analysis• PREs associated with TC Frances (2004) and TC
Rita (2005)• Concluding remarks
Motivation
• Identify preferential dynamic and thermodynamic configurations for PREs to improve forecasts
• Establish physical mechanisms accounting for different spatial and temporal characteristics of PREs
TC Frances12Z 8 Sep 2004
TC Rita06Z 25 Sep 2005
66 66PRE
PRE
Motivation
Definition of a PRE
• Defined as distinct mesoscale regions of heavy rainfall [~100 mm (24 h)−1] ~1000 km downstream of landfalling and recurving TCs (Cote 2007)
• Develop as a poleward stream of deep moisture from the TC interacts with a baroclinic environment
Conceptual model from Bosart and Carr (1978) for a rain event associated with TC Agnes (1972)
Data and Methodology
• PREs for 1988–2008 identified using:• National base reflectivity radar mosaics (cases during
1995–2008)• 1° GFS analyses and 2.5° NCEP–NCAR reanalysis data • NCDC Hourly Precipitation Dataset• NPVU QPE • UPD
• PREs stratified by TC recurvature at time of PRE initiation
• Pre-recurvature – no component of TC motion vector in the positive x-direction• Post-recurvature – component of TC motion vector in
the positive x-direction
Data and Methodology
• TC-relative compositing:– 6 hourly 2.5° NCEP–NCAR grids for PRE cases were
shifted so that TCs were located at same position– PRE cases were stratified into pre- and post-
recurvature categories and composited at time of initiation
– Cases which deviated significantly in synoptic environment were excluded
– Only one PRE from each parent TC was used in compositing
PREs 1988−2008
PRE-REC
URVATURE
POST-RECURVATURE
05
10152025303540
Num
ber o
f PRE
s
PRE-REC
URVATURE
POST-REC
URVATURE0
5
10
15
20
25
DURA
TIO
N (h
)
• 65 PREs associated with 37 TCs• Pre-recurvature category is
characterized by larger separation distance and longer duration
Concluding RemarksKey features of composites– Pre-recurature PREs• PRE develops in equatorward entrance region of
anticyclonically curved upper-level jet streak
• Upper-level flow characterized by ridge overlying the TC and broad, positively tilted trough well upstream and poleward of TC
• Low-level anticyclone downstream of TC facilitates poleward flow towards zonally oriented baroclinic zone frontogenetical forcing, moisture transport from the TC
Concluding RemarksKey features of composites– Post-recurvature• PRE develops in equatorward entrance region of
anticyclonically curved upper-level jet streak
• TC much closer to axis of upstream trough and jet streak
• TC circulation impinges upon low-level baroclinic zone
• Frontogenetical forcing at the terminus of low-level jet associated with TC circulation and downstream anticyclone
• Tropical moisture plume extends poleward and eastward along a SW−NE oriented baroclinic zone
Case studies– Rita (2005): Pre-recurvature PRE
• PRE was quasi-stationary and long-lived• PRE developed along zonal baroclinic zone in equatorward
entrance region of upper-level jet• Anticyclone over the eastern U.S. aided in the transport of TC
moisture to region of lift– Frances (2004): Post-recurvature PRE
• PRE was small-scale and quasi-stationary• PRE developed on the warm side of baroclinic zone in
equatorward entrance region of upper-level• Strong low-level flow associated with TC and downstream ridge
was associated with moisture transport and warm air advection