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
PRE-RECURVATURE POST-RECURVATURE300
500
700
900
1100
1300
1500
SEPA
RATI
ON
DIS
TAN
CE (k
m)
29
34
N=63
TC-Relative Composites
Pre-recurvature PREs Post-recurvature PREsN=12 N=13
kts
200 hPa heights (dam, black), winds (kts, barbs ≥40 kts), wind speed (kts, shaded ≥50 kts); 850 hPa relative vorticity (10−5 s−1, blue)
200 hPa
TC-Relative Composites
Pre-recurvature PREs Post-recurvature PREsN=12 N=13
mm
700 hPa heights (dam, black), 500-850 hPa layer-averaged wind (kts, barbs ≥10kts), total column precipitable water (mm, shaded)
700 hPa
TC-Relative Composites
Pre-recurvature PREs Post-recurvature PREsN=12 N=13
850 hPa heights (dam, black), Q-vectors (10 −11 K m −1 s −1), Q-vector convergence (10 −16 K m −2 s−1, shaded), potential temperature (K, red)
850 hPa
10 −16 K m −2 s −1
PRE associated with TC Rita 24–26 Sep 2005Pre-recurvature PRE
1200 UTC 24 Sep – 0000 UTC 26 Sep 2005: 200 hPa mean geopotential height (dam, black), wind speed (≥70 kts, red), and total precipitation (mm, shaded)
mm
00Z25 Sep
06Z19 Aug
03Z25 Sep
06Z25 Sep
12Z25 Sep
Source: NCAR case selection archive
Radar EvolutionWSR-88D base reflectivity
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
0600 UTC 25 Sep 2005
850 hPa 200 hPa
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
0600 UTC 25 Sep 2005
850 hPa Pre-recurvature composite
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−2 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
0600 UTC 25 Sep 2005
200 hPaPre-recurvature composite
1200 UTC 7 Sep – 0000 UTC 9 Sep 2004: 200 hPa mean geopotential height (dam, black), wind speed (≥70 kts, red), and total precipitation (mm, shaded)
mm
PRE associated with TC Frances 7–8 Sep 2004Post-recurvature PRE
Radar Evolution
06Z8 Sep
12Z08 Sep
09Z8 Sep
15Z8 Sep
Source: NCAR case selection archive
WSR-88D base reflectivity
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
1200 UTC 8 Sep 2004
850 hPa 200 hPa
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
1200 UTC 8 Sep 2004
Post-recurvature composite850 hPa
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−2 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
1200 UTC 8 Sep 2004
Post-recurvature composite 200 hPa
PREs in context of extreme rain producing MCSs
Frontal type flash flood pattern from Maddox et al. (1979)
PRE Composite
Surface 1000 hPa winds (m s−1), heights (dam), θe (K)
66
LH
5 m s−1
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
Concluding Remarks