Mesoscale Precipitation Structures Accompanying Landfalling and Transitioning Tropical Cyclones in the Northeast United States Jared Klein, Lance F. Bosart, and Daniel Keyser University at Albany/SUNY; Albany, NY CSTAR II Grant NA04NWS David Vallee NWS Weather Forecast Office; Taunton, MA CSTAR Spring Meeting 4 May 2007

Objectives  Examine the distribution of rainfall in relation to the tropical cyclone (TC) track and identify smaller-scale areas of enhanced rainfall.  Identify key mesoscale and synoptic-scale features that routinely accompany these landfalling and transitioning TCs.  Understand how heavy precipitation is modified by interactions of these features in the presence of complex physiography of the Northeast.

Complex Topography of the Northeast United States

Motivation Predicting timing and location of mesoscale features accompanying heavy precipitation is difficult. Approximately 4 out of every 5 fatalities from landfalling TCs are directly caused by inland flash flooding (Rappaport 2000). Recent active TC seasons (2004 and 2005) have led to an increase in the frequency of TC related flooding events over the Northeast. –1950 – 2003: Average of 1 event every year –2004 – 2005: 10 events in 2 years

Previous CSTAR Work (DeLuca 2004)

Data and Methodology Identify TCs which produced ≥100 mm (4 in.) of rainfall from Determine track versus precipitation distribution. –NCEP 24 h daily ( UTC) UPD for cases prior to 2004 –RFC NPVU archived QPE –NCEP HPC 24 h and storm total precipitation maps –NHC best-track data Identify synoptic and mesoscale processes associated with heavy precipitation. –Q vector analyses 2.5° NCEP/NCAR reanalysis for storms prior to ° GFS dataset for storms past 2003 –Archived surface data

Q Vector Partitioning in Natural Coordinates Source: Martin (1999) Q vector- Examines regions of horizontal ageostrophic motion Q Convergence- QG forcing for ascent Q s - Rotation of Q s Convergence- Analogous to advection of geostrophic relative vorticity by the thermal wind Q n - Frontogenesis Q n Convergence- Forcing for vertical motion within and parallel to frontal zones

52 TCs producing ≥ 4 inches of rainfall in the Northeast U.S. during the period 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 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

Preliminary Results

Upper-level downstream ridge and jet development. –Occurred in nearly every case –Placed Northeast in equatorward entrance region of jet –Amplified lower-level jet and positive θ e advection Enhanced precipitation as TC interacts with a pre- existing mesoscale boundary or coastal front. –Found in almost every case –Heavy precipitation region along and in cold sector of coastal front (CF) –Stronger θ gradient when interacting with a upstream midlatitude trough during extratropical transition (ET) Preliminary Results (cont.)

Possible orographic enhancement of precipitation. –Occurred in almost half the cases –Track far enough inland so that low-level easterly flow ahead of storm was upslope on the eastern sides of the Appalachian Mountains –Highest incidence over Blue Ridge, Catskills, Berkshires, and White Mountains Preliminary Results (cont.)

TC Tracks Impacting the Northeast (1999–2006) Mesoscale Features : Cool Colors- Frontogenesis Green- Orographic Warm Colors- Both features

Case Study 1: Ivan 17–18 September 2004 LOT precipitation distribution. Mesoscale frontogenesis along a pre-existing synoptic boundary. Possible orographic precipitation enhancement.

Total precipitation (in.) versus track (1200–1200 UTC) 16–19 Sep 2004 LOT Precip Distribution

Ivan: 300 and 925 hPa Analysis 1200 UTC September UTC 16 September hPa Heights (dam), Wind Speed (m s -1 ), and Divergence (10 -5 s -1 ) WSI Radar, 925 θ e (K) and Wind Barbs (kt) Upstream baroclinic zone

Ivan: 300 and 925 hPa Analysis 1200 UTC September hPa Heights (dam), Wind Speed (m s -1 ), and Divergence (10 -5 s -1 ) WSI Radar, 925 θ e (K) and Wind Barbs (kt) 1200 UTC 17 September 2004 Northeastward extension of precip field Confluent flow in right jet-entrance region

Ivan: 300 and 925 hPa Analysis 1200 UTC September hPa Heights (dam), Wind Speed (m s -1 ), and Divergence (10 -5 s -1 ) WSI Radar, 925 θ e (K) and Wind Barbs (kt) 1200 UTC 18 September 2004 Strengthening downstream ULJ and ridge

Q Vector Examination –1200 UTC 17 September 2004 Q vectors (10 −10 K m −1 s −1 beginning at 2.5 × 10 −11 ), potential temperature (K) contoured in green, and Q divergence (convergence) (10 −15 K m −2 s −1 ) shaded in cool (warm) colors. Q at 925 hPa Q n at 925 hPa Q s at 925 hPa Q n at 300 hPa Deep frontogenesis in jet-entrance region Structure has westward tilt w/ height

Q vectors (10 −10 K m −1 s −1 beginning at 2.5 × 10 −11 ), potential temperature (K) contoured in green, and Q divergence (convergence) (10 −15 K m −2 s −1 ) shaded in cool (warm) colors. Q at 925 hPa Q n at 925 hPa Q s at 925 hPa Radar at 1200 UTC 17 September 2004 Q Vector Examination –1200 UTC 17 September 2004

Q Vector Examination –0000 UTC 18 September 2004 Q vectors (10 −10 K m −1 s −1 beginning at 2.5 × 10 −11 ), potential temperature (K) contoured in green, and Q divergence (convergence) (10 −15 K m −2 s −1 ) shaded in cool (warm) colors. Radar at 1200 UTC 17 September 2004 Q at 925 hPa Q n at 925 hPa Q s at 925 hPa Radar at 0000 UTC 18 September 2004 Q s con.(div.) near thermal ridge(trough) Highest reflectivity over frontogenesis region

Q Vector Examination –1200 UTC 18 September 2004 Q vectors (10 −10 K m −1 s −1 beginning at 2.5 × 10 −11 ), potential temperature (K) contoured in green, and Q divergence (convergence) (10 −15 K m −2 s −1 ) shaded in cool (warm) colors. Radar at 1200 UTC 17 September 2004 Q at 925 hPa Q n at 925 hPa Q s at 925 hPa Radar at 0000 UTC 18 September 2004Radar at 1200 UTC 18 September 2004

Surface Q n Vectors –0000 UTC 18 September 2004 Surface Q n vectors (10 −10 K m −1 s −1 beginning at 1.0 × 10 −10 ), potential temperature (K), streamlines, and Q n divergence (convergence) (10 −14 K m −2 s −1 ). Flow of tropical air into mesoscale boundary

6-h precipitation (in.) ending at 0600 UTC 18 September Heaviest 6-h precip along and on cold side of boundary

Surface Q n Vectors –0600 UTC 18 September 2004 Surface Q n vectors (10 −10 K m −1 s −1 beginning at 1.0 × 10 −10 ), potential temperature (K), streamlines, and Q n divergence (convergence) (10 −14 K m −2 s −1 ).

6-h precipitation (in.) ending at 1200 UTC 18 September Heaviest 6-h precip along and on cold side of boundary

Case Study 2: Ernesto 31 August – 2 September 2006 ROT precipitation distribution. Coastal frontogenesis.

Total precipitation (in.) versus track (1200–1200 UTC) 31 Aug–03 Sep 2006 ROT Precip Distribution

Ernesto: 300 and 925 hPa Analysis 1200 UTC 31 August – 1 September hPa Heights (dam), Wind Speed (m s -1 ), and Divergence (10 -5 s -1 ) WSI Radar, 925 θ e (K) and Wind Barbs (kt) 1200 UTC 31 August 2006 Jet much further downstream than with Ivan

Ernesto: 300 and 925 hPa Analysis 1200 UTC 31 August – 1 September hPa Heights (dam), Wind Speed (m s -1 ), and Divergence (10 -5 s -1 ) WSI Radar, 925 θ e (K) and Wind Barbs (kt) 1200 UTC 01 September 2006 Heaviest precip near LLJ/ θ e ridge axis

Q vectors (10 −10 K m −1 s −1 beginning at 2.5 × 10 −11 ), potential temperature (K) contoured in green, and Q divergence (convergence) (10 −15 K m −2 s −1 ) shaded in cool (warm) colors. Q at 925 hPa Q n at 925 hPa Q s at 925 hPa Q Vector Examination –1200 UTC 31 August 2006 No strong frontogenesis

Q vectors (10 −10 K m −1 s −1 beginning at 2.5 × 10 −11 ), potential temperature (K) contoured in green, and Q divergence (convergence) (10 −15 K m −2 s −1 ) shaded in cool (warm) colors. Q at 925 hPa Q n at 925 hPa Q s at 925 hPa Radar at 1200 UTC 17 September 2004 Q Vector Examination –0000 UTC 01 September 2006 Frontogenesis along CF as Ernesto nears landfall Strong forcing for ascent associated with both Q s and Q n con.

Q vectors (10 −10 K m −1 s −1 beginning at 2.5 × 10 −11 ), potential temperature (K) contoured in green, and Q divergence (convergence) (10 −15 K m −2 s −1 ) shaded in cool (warm) colors. Q at 925 hPa Q n at 925 hPa Q s at 925 hPa Radar at 1200 UTC 17 September 2004 Q Vector Examination –1200 UTC 01 September 2006 Highest reflectivity near strongest Q con. Largest Q con. ROT

Surface Q n Vectors –0600 UTC 01 September 2006 Surface Q n vectors (10 −10 K m −1 s −1 beginning at 1.0 × 10 −10 ), potential temperature (K), streamlines, and Q n divergence (convergence) (10 −14 K m −2 s −1 ). Banded Qn con. – div. structure along frontogenesis region

Surface Q n vectors (10 −10 K m −1 s −1 beginning at 1.0 × 10 −10 ), potential temperature (K), streamlines, and Q n divergence (convergence) (10 −14 K m −2 s −1 ). Surface Q n Vectors –1200 UTC 01 September 2006 Heaviest 6-h precip ROT along and north of mesoscale boundary

Surface Q n vectors (10 −10 K m −1 s −1 beginning at 1.0 × 10 −10 ), potential temperature (K), streamlines, and Q n divergence (convergence) (10 −14 K m −2 s −1 ). Surface Q n Vectors –1800 UTC 01 September 2006 Heaviest 6-h precip ROT along and north of mesoscale boundary

Summary of Case Studies Heaviest precipitation occurred over areas where strong surface frontogenesis, Q s and Q n forcing for ascent were present. –Northward stretching of precipitation field over areas of Q n forcing for ascent –Effects of Q s motions led to thermal trough/ridge development over the eastern U.S. –Deep frontogenesis in equatorward jet entrance region

Interaction between downstream jet and upstream trough important for determining LOT versus ROT precipitation distribution. TCs’ large circulation induced an influx of tropical air over a distinct mesoscale boundary. Summary of Case Studies (cont.)

Adapt a detailed conceptual model applicable to operational forecasters. Convert research findings into a training session for NWS forecasters as mentioned by David Vallee. –Incorporate: –Climatology results –Q vector method for analyzing mesoscale precipitation structures Technology Transfer

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