Predecessor Rain Events in Tropical Cyclones Matthew R. Cote 1, Lance F. Bosart 1, Daniel Keyser 1, and Michael L. Jurewicz, Sr 2 1 Department of Earth and Atmospheric Sciences University at Albany, SUNY, Albany, NY 2 National Weather Service Forecast Office Binghamton, NY CSTAR II Grant NA04NWS Ninth Northeast Regional Operational Workshop Albany, New York, Thursday 8 November 2007

1200 UTC 8 Sep'04

Surface ______ SLP (hPa) ______  (K) 1200 UTC 8 Sept ‘04

OUTLINE Explain the PRE identification process Present climatology and statistics of PREs for 1998–2006 Show a synoptic-scale flow composite at time of PRE initiation Examine the synoptic-scale and mesoscale factors important in producing two PREs ahead of Gaston (2004)

DATA SOURCES NCDC and WSI NOWRAD radar imagery NHC best-track data NPVU QPE and NWS rainfall products NCEP/NARR gridded datasets

IDENTIFYING PREs: 1998–2006 Coherent area of rain displaced poleward of TC Maximum rainfall rates exceeded 100 mm in 24 h Moisture transport from TC toward PRE 1800 UTC WSI NOWRAD Radar Mosaic PRE Gaston

IDENTIFYING PREs: 1998–2006 Coherent area of rain displaced poleward of TC Maximum rainfall rates exceeded 100 mm in 24 h Moisture transport from TC toward PRE 47 PREs associated with 21 TCs were identified (~2 PREs per TC) ~1/3 of all U.S. landfalling TCs produced at least one PRE Five cases where TC did not make U.S. landfall

SEPARATION BY TC TRACK SIMILARITY

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

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

Bosart and Carr (1978) conceptual model of antecedent rainfall PAST RESEARCH ON PRE WITH AGNES (1972)

Separation Distance 1086 ± 482 km Median: 935 km Bosart and Carr (1978) conceptual model of antecedent rainfall PRE STATISTICS

Separation Distance 1086 ± 482 km Median: 935 km Event Duration 14 ± 7 h Median: 12 h Bosart and Carr (1978) conceptual model of antecedent rainfall PRE STATISTICS

Bosart and Carr (1978) conceptual model of antecedent rainfall PRE STATISTICS Separation Distance 1086 ± 482 km Median: 935 km Event Duration 14 ± 7 h Median: 12 h Time Lag 45 ± 29 h Median: 36 h

PRE TRACK-RELATIVE POSITIONS PRE Locations Relative to TC Track 1998–2006

PRE TRACK-RELATIVE POSITIONS PRE Locations Relative to TC Track 1998–2006 Potential for flooding in areas not directly impacted by TC rainfall

PRE TRACK-RELATIVE POSITIONS PRE Locations Relative to TC Track 1998–2006 Potential for excessive flooding beginning before arrival of TC rainfall

SE RECURVATURE PRE COMPOSITE TIME OF PRE INITIATION 700 hPa Ht (dam) and UVM (μb s -1 )925 hPa Ht (dam), θ e (K), and 200 hPa wind speeds (m s -1 ) Significant midlevel trough with weak UVM well poleward of TC Deep meridional flow transports tropical moisture up East Coast PRE forms: - in right-entrance region of intensifying upper-level jet -on western edge of θ e ridge

GASTON (2004)

Radar Overview 0000 UTC WSI NOWRAD Radar Mosaic Gaston PRE 2 PRE UTC WSI NOWRAD Radar Mosaic Gaston PRE 1

925 hPa h (dam), θ e (K), and 200 hPa wind speed (m s -1 ) 700 hPa h (dam) and WSI NOWRAD reflectivity (dBZ) 2100 UTC 30 Aug'04 Maddox et al. (1979) Frontal Flash Flood Pattern Ridge axis Developing PRE Trough axis Gaston

925 hPa h (dam), θ e (K), and 200 hPa wind speed (m s -1 ) 700 hPa h (dam) and WSI NOWRAD reflectivity (dBZ) 2100 UTC 30 Aug'04 Maddox et al. (1979) Mesohigh Flash Flood Pattern Ridge axis Developing PRE Trough axis Gaston

a b c 1200 UTC 30 Aug 2004 SLP (hPa) and radar reflectivity (dBZ)Streamlines, q (g kg -1 ) and MFC (shaded  s -1 )  (K) and gradient (shaded every 2.5  K m -1 ) PRE 2 Weak Low

1200 UTC 30 Aug 2004 Cross section: 43.5°N, 79°W to 41°N, 72.5°W.  e (dashed red), UVM (blue every 3 micro μs -1 below 3 μ s -1 ), relative humidity (shaded every 10% above 70%), frontogenesis (shaded K (100 km) -1 (3 h) -1 ), and winds (kt). Buffalo (72518; BUF), NY, skew T-log p diagram: 1200 UTC 30 Aug 2004

SLP (hPa) and radar reflectivity (dBZ)Streamlines, q (g kg -1 ) and MFC (shaded  s -1 )  (K) and gradient (shaded every 2.5  K m -1 ) a 2100 UTC 30 Aug 2004 b c PRE 2 PRE 3

SLP (hPa) and radar reflectivity (dBZ)Streamlines, q (g kg -1 ) and MFC (shaded  s -1 )  (K) and gradient (shaded every 2.5  K m -1 ) a 0000 UTC 30 Aug 2004 b c PRE 2 PRE 3

2100 UTC 30 Aug 2004 Cross section: 43.5°N, 79°W to 41°N, 72.5°W.  e (dashed red), UVM (blue every 3 μs -1 below 3 micro μ s -1 ), relative humidity (shaded every 10% above 70%), frontogenesis (shaded K (100 km) -1 (3 h) -1 ), and winds (kt). Gray (74389; GYX), ME, skew T-log p diagram: 0000 UTC 10 Aug 2004

ML Streamlines Representative TC Tracks TC Rainfall PREs LL θ e -Ridge Axis See inset UL Jet CONCEPTUAL MODEL: LOT PREs AHEAD OF SR OR AR TCs Revised and updated from Fig. 13 of Bosart and Carr (1978)

ML Streamlines Representative TC Tracks TC Rainfall PREs ML θ e -Ridge Axis UL Jet LL θ e -Ridge Axis PREs Mountain Axes Idealized LL Winds LL Temp/Moisture Boundary CONCEPTUAL MODEL: LOT PREs AHEAD OF SR OR AR TCs

~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 LOT PREs are most common, but AT PREs produce the risk of most extreme flooding CONCLUSIONS

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 θ e gradient along and just on the “cool” side of a surface boundary Near a low-level θ e -ridge axis on the “warm” side of the surface boundary In areas of orographic uplift CONCLUSIONS Gaston (2004) case study illustrates that favored locations for PRE development are: