Lance F. Bosart , and Daniel Keyser University at Albany/SUNY; Albany, NY

1. Examining the Distribution of Precipitation Associated with Landfalling and Transitioning Tropical Cyclones in the Northeastern U.S. Lance F. Bosart, and Daniel Keyser University at Albany/SUNY; Albany, NY David DeLuca Jared Klein (former student at SUNY) (WFO LWX) Mike Evans Mike Jurewicz (WFO BGM) (WFO BGM) David Vallee John Cannon (NWS/NERFC) (WFO GYX)

2. Objectives • Examine precipitation distribution relative to the tropical cyclone track • Identify processes which lead to these distributions and quantity of precipitation • Impact of downstream ridge/jet development on precipitation distribution • Impact of mesoscale structures on precipitation • Examine the recurvature and acceleration of landfalling TC’s in the Northeast

3. Motivation • Significant damage and loss of life • Connie and Diane 1955 • Agnes 1972, Floyd 1999 • Ivan, Jeane 2005, Ernesto 2006 • Forecast difficulties relating to QPF • Each tropical cyclone was under some form of extra-tropical transition (ET) • Most were accelerating toward the region • Mobile trough interactions • Coastal frontogenesis • Orographic enhancement/modulation • Develop improved synoptic awareness and forecast skill

4. CSTAR Background • The Collaborative Science, Technology and Applied Research (CSTAR) Program • State University of New York at Albany • Focused on Improving the Prediction of Cool- and Warm-Season Heavy Precipitation Events over the Northeast United States • Warm Season Project • Improving the Prediction of the Timing and Intensity of Heavy Precipitation Associated with Landfalling Tropical Cyclones, as Modulated by the Complex Terrain and Physiography of the Northeastern United States”. SUNY Albany CSTAR Region

5. CSTAR Background • CSTAR I • Allowed us to identify different rainfall orientations and the synoptic scale mechanisms that produce these orientations. • CSTAR II • Examine mesoscale structures associated with LFTC in the NE and their affect on rainfall distribution • Develop an ingredients based approach to forecasting the rainfall associated with these systems. • Branch project (D. Vallee/J. Cannon) picked apart the subset of land falling storms from a recurvature and acceleration stand point • CSTAR III • Examine “Pre-tropical Cyclone” Flash Flood Events

6. Historical PerspectiveHeavy Rainfall Distribution

7. Historical Perspective – August ’55Widespread Flooding/Flash Flooding City of Woonsocket, RI – Diane 1955 Flooded downtown “social/business” district Providence Journal Route 44 west – Putnam, CT Tropical Storm Diane, 1955 18.15 inches of rain in1 day in Westfield, MA USACE NE Division

8. 52 TCs producing ≥ 4 inches of rainfall in the Northeast U.S. during the period 1950 – 2006red denotes “coastal frontogenesis” 1979 David 1985 Gloria 1988 Chris 1991 Bob 1996 Bertha 1996 Edouard 1996 Fran 1997 Danny 1998 Bonnie 1999 Floyd 2001 Allison 2002 Isidore 2002 Kyle 2003 Bill 2003 Isabel 2004 Alex 2004 Bonnie 2004 Charley 2004 Frances 2004 Gaston 2004 Ivan 2004 Jeanne 2005 Cindy 2005 Katrina 2005 Ophelia 2006 Ernesto 1950 Able 1950 Dog 1952 Able 1953 Barbara 1953 Carol 1954 Carol 1954 Edna 1954 Hazel 1955 Connie 1955 Diane 1955 Ione 1958 Helene 1959 Cindy 1959 Gracie 1960 Brenda 1960 Donna 1961 Esther 1962 Alma 1962 Daisy 1963 Ginny 1969 Gerda 1971 Doria 1971 Heidi 1972 Agnes 1972 Carrie 1976 Belle

9. Heavy Rainfall • Two types of distributions • Along/Right of Track • Left of Track • Some systems “changed phase” as they turned and accelerated northeastward • Nearly every tropical cyclone studied was going through some degree of extra-tropical transition • Nearly ½ of all our storms produced small stream/river flooding in the region! • Average rainfall 6-8 inches

10. Climatology Results LOT = left of track ROT = right of track

11. Features Contributing to Heavy Precipitation over the Northeast US Accompanying Landfalling and Transitioning Tropical Cyclones

12. Interaction with the Westerlies Hurricane Carol (t-48 hrs)Jet prepositioned to the east Hurricane Floyd (t-48 hrs) Jet prepositioned to the northwest

13. Interaction with the Westerlies Hurricane Carol (t-24 hrs) Acceleration Commences Hurricane Floyd (t-24 hrs) Acceleration Commences

14. Interaction with the Westerlies Hurricane Carol (t=0 Landfall) Northward motion ~ 39 mph Hurricane Floyd (t-0 hrs Landfall) North-northeast motion ~ 33 mph

15. CSTAR II Objectives • Examine the distribution of rainfall in relation to tropical cyclone (TC) track and identify smaller-scale areas of enhanced rainfall accompanying landfalling and transitioning TCs in the Northeast U.S. • Identify key mesoscale processes that impact the precipitation distribution for these TCs. • Upstream thermal trough and downstream thermal ridge–jet interactions • Upper-level jet (ULJ) and lower-level jet (LLJ) interactions • TC-induced coastal frontogenesis • Orographic precipitation enhancement

16. Summary of Case Studies: Conceptual Model 1 Upper-level jet streak Qn div Qn con Heavy rainfall LLJ Qs con Qs div low-level Qn low-level θ sfc boundary

17. Summary of Case Studies: Conceptual Model 2 Z Z θ θ Cold Warm Cold Warm LOT Precipitation Distribution ROT Precipitation Distribution Deep frontogenesis tilting toward cold air w/height Strongest frontogenesis focused near surface

18. Ivan vs. Ernesto LOT Precip Distribution ROT Precip Distribution Ernesto Ivan

19. Ivan vs. Ernesto Comparison Confluent flow in equatorward jet-entrance region Region of significant 925 mbFrontogenesis Jet much farther downstream than with Ivan Absence of significant 925 mbFrontogenesis

20. Ivan vs. Ernesto Comparison Strengthening downstream ULJ and ridge Strong 925 mbfrontogenesis Jet remains farther downstream than with Ivan Modest frontogenesis – remains shallow (<700 mb)

21. Ivan vs. Ernesto Comparison Deep frontogenesis tilting toward cold air w/height Ernesto Ivan

22. CSTAR III Objectives • Examine the distribution and behavior of heavy flash flood producing systems in advance of Tropical Cyclones • “PREs” • Events typically precede arrival of TC Core by 24-48 hours • Forecasters are focused on the TC and are “surprised” by evolution of flash flooding

23. Defining a “PRE” • Defined as a distinct mesoscale region of heavy rainfall (100 mm/24 hr) and ~ 1000 km downstream of a landfalling and/or recuring TC • Development is driven by interaction of poleward stream of deep moisture associated with the TC and upper level jet entrance region and a baroclinic environment • 1998-2006: 47 PREs occurred associated with 21 TCs. • 1/3 of all U.S. Landfalling TC’s produced at least one PRE. • Classifications of PRE were subject to the following standards: • 100 mm (4”) of rainfall within a 24-hour period • Well defined region of precipitation (not scattered / isolated convection • Well established moisture connection between the TC and PRE • In addition to previous criteria: • Clear separation between TC rainfall shield and PRE • At least 35 dBz returns within PRE centroid for 6 hours or more

24. PRE region 6 6 Hurricane Frances 2004 1200 UTC 8 Sep'04

26. SOUTHEAST RECURVATURES • 7/11 (64%) produced at least one PRE • 16 PREs from 7 TCs • Influential geographical features: • - Gulf of Mexico - Atlantic Ocean - Appalachians • Approximate point of PRE formation

27. ATLANTIC RECURVATURES • 6/15 (40%) produced at least one PRE • 12 PREs from 6 TCs • Influential geographical features: • - Atlantic Ocean - Appalachians • Approximate point of PRE formation

28. Conceptual Model: LOT PRE Ahead Of SR Or AR TC UL Jet LL θe-Ridge Axis PREs See inset Mid-level Streamlines TC Rainfall Revised and updated from Fig. 13 of Bosart and Carr (1978) Representative TC Tracks

29. CONCLUSIONS PRE • ~1/3 of U.S. landfalling TCs produce at least one PRE, but landfall is not necessary • TCs recurving over the Southeast and along the East Coast have the greatest likelihood of producing PREs • PREs form ~1000 km away from their parent TCs and ~1–2 days in advance • PRE’s form ahead of a midlevel short-wave trough and near a midlevel ridge axis • In the right-entrance region of an upper-level jet within a low-level θe gradient along and just on the “cool” side of a surface boundary • Near a low-level θe-ridge axis on the “warm” side of the surface boundary (the moisture plume) • In areas of orographic uplift 6 6 PRE 6 6

30. Recurvature/Acceleration

31. Study Outline • Produce reanalyses for landfallingTC’s on the New England coast • Create composites for each “flavor” to the pattern accelerating storm northward • Have established Type A and Type B patterns • Placement of trough axis and jet structures are key • Typical jet cores are 2 or more standard deviations above climatology with land falling systems

32. Type A Storms Carol ’54 Alma ’66 Gerda ‘69 Doria ’71 Heidi ’71 Belle ’76 Bob ’91 Bertha ’96 Type B Storms Edna ’54 Cindy ‘59 Brenda ‘60 Donna ’60 Carrie ’72 Gloria ’85 Floyd ’99 Charley ’04 Hermine ‘04 Storms includedPeriod 1950-2006 Not sure! • Diane ’55 • Esther ‘61 • Henri ‘85

33. Vallee/Cannon - Type A PatternEvolution of Closed Low Vicinity of the Ohio ValleyJet prepositioned to the east

34. LF-72 hrs

35. LF-48 hrs

36. LF-36 hrs

37. LF-24 hrs

38. LF-12 hrs

39. Landfall

40. Vallee/Cannon - Type B PatternIndependent short waves rotating through a mean long wave trough just inland of the East Coast

41. LF-72 hrs

42. LF-48 hrs

43. LF-36 hrs

44. LF-24 hrs

45. LF-12 hrs

46. Landfall

47. Summary Two very distinct patterns have evolved which foster recurvature and acceleration into New England. Type A – Closed low Lakes/Ohio Valley Type B – Mean long wave with intense disturbances rotating through Pre-positioning of the assets is critical Type A features a pre-existing jet to our east Type B features a pre-existing jet to our west Both types featured strong Bermuda High offshore When/how system is captured with respect to evolution of mid latitude trough interaction seems to dictate how swiftly this all occurs Hurricane Earl – global model performance validated our findings; Earl remained offshore – trough axis lagged behind (west) of our composite for proper placement

48. What remains?Understanding the behavior/decay of the west side wind fields! • Series of tropical cyclones passing just off the coast have resulted in a gross over-forecasting of the west side wind fields along the northeast coast • Complex boundary layer and thermodynamic processes are at play as the system undergoes ET • Current statistical methods fail to capture these processes • We need help in understanding this!