Benjamin J. Moore, Lance F. Bosart , and Daniel Keyser

1. 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 NOAA/CSTAR Grant NA07NWS4680001

2. 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

3. Motivation • Identify preferential dynamic and thermodynamic configurations for PREs to improve forecasts • Establish physical mechanisms accounting for different spatial and temporal characteristics of PREs

4. Motivation PRE PRE 6 6 6 6 TC Frances 12Z 8 Sep 2004 TC Rita 06Z 25 Sep 2005

5. 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)

6. 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

7. 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

8. PREs 1988−2008 34 29 • 65 PREs associated with 37 TCs • Pre-recurvature category is characterized by larger separation distance and longer duration N=63

9. TC-Relative Composites 200 hPa Pre-recurvature PREs Post-recurvature PREs N=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)

10. TC-Relative Composites 700 hPa Pre-recurvature PREs Post-recurvature PREs N=12 N=13 mm 700 hPa heights (dam, black), 500-850 hPa layer-averaged wind (kts, barbs ≥10kts), total column precipitable water (mm, shaded)

11. TC-Relative Composites 850 hPa Pre-recurvature PREs Post-recurvature PREs N=12 N=13 10 −16 K m −2 s −1 850 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)

12. PRE associated with TC Rita 24–26 Sep 2005 Pre-recurvature PRE mm 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)

13. Radar Evolution WSR-88D base reflectivity 00Z 25 Sep 03Z 25 Sep 06Z 19 Aug 06Z 25 Sep 12Z 25 Sep Source: NCAR case selection archive

14. Synoptic Environment 0600 UTC 25 Sep 2005 850 hPa 200 hPa kts mm 850 hPa heights (dam, black), Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded) 200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded); 850 hPa relative vorticity (10−5 s−1, blue)

15. Synoptic Environment 0600 UTC 25 Sep 2005 Pre-recurvature composite 850 hPa kts mm 850 hPa heights (dam, black), Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded) 200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded); 850 hPa relative vorticity (10−5 s−1, blue)

16. Synoptic Environment 0600 UTC 25 Sep 2005 Pre-recurvature composite 200 hPa kts mm 850 hPa heights (dam, black), Q-vectors (10−11 K m−2 s−1), potential temperature (K, red), total column precipitable water (mm, shaded) 200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded); 850 hPa relative vorticity (10−5 s−1, blue)

17. PRE associated with TC Frances 7–8 Sep 2004 Post-recurvature PRE mm 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)

18. Radar Evolution WSR-88D base reflectivity 06Z 8 Sep 09Z 8 Sep 15Z 8 Sep 12Z 08 Sep Source: NCAR case selection archive

19. Synoptic Environment 1200 UTC 8 Sep 2004 850 hPa 200 hPa kts mm 850 hPa heights (dam, black), Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded) 200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded); 850 hPa relative vorticity (10−5 s−1, blue)

20. Synoptic Environment 1200 UTC 8 Sep 2004 Post-recurvature composite 850 hPa kts mm 850 hPa heights (dam, black), Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded) 200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded); 850 hPa relative vorticity (10−5 s−1, blue)

21. Synoptic Environment 1200 UTC 8 Sep 2004 200 hPa Post-recurvature composite kts mm 850 hPa heights (dam, black), Q-vectors (10−11 K m−2 s−1), potential temperature (K, red), total column precipitable water (mm, shaded) 200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded); 850 hPa relative vorticity (10−5 s−1, blue)

22. PREs in context of extreme rain producing MCSs PRE Composite Frontal type flash flood pattern from Maddox et al. (1979) 1000 hPa winds (m s−1), heights (dam), θe (K) Surface L H 6 6 5 m s−1

23. Concluding Remarks Key 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

24. Concluding Remarks Key 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

25. Concluding Remarks 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