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Predecessor Rain Events in Tropical Cyclones

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.

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Predecessor Rain Events in Tropical Cyclones

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  1. Predecessor Rain Events in Tropical Cyclones Matthew R. Cote1, Lance F. Bosart1, Daniel Keyser1, and Michael L. Jurewicz, Sr2 1Department of Earth and Atmospheric Sciences University at Albany, SUNY, Albany, NY 2National Weather Service Forecast Office Binghamton, NY CSTAR II Grant NA04NWS4680005 Ninth Northeast Regional Operational Workshop Albany, New York,Thursday 8 November 2007

  2. 1200 UTC 8 Sep'04

  3. Surface ______SLP (hPa) ______  (K) 1200 UTC 8 Sept ‘04

  4. 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)

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

  6. 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 PRE Gaston 1800 UTC 040830 WSI NOWRAD Radar Mosaic

  7. 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

  8. SEPARATION BY TC TRACK SIMILARITY

  9. 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

  10. 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

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

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

  13. 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

  14. 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 Bosart and Carr (1978) conceptual model of antecedent rainfall

  15. PRE TRACK-RELATIVE POSITIONS PRE Locations Relative to TC Track 1998–2006 26 12 9

  16. PRE TRACK-RELATIVE POSITIONS PRE Locations Relative to TC Track 1998–2006 Potential for flooding in areas not directly impacted by TC rainfall 26 12 9

  17. PRE TRACK-RELATIVE POSITIONS PRE Locations Relative to TC Track 1998–2006 Potential for excessive flooding beginning before arrival of TC rainfall 26 12 9

  18. SE RECURVATURE PRE COMPOSITE TIME OF PRE INITIATION 700 hPa Ht (dam) and UVM (μb s-1) 925 hPa Ht (dam), θe (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 θe ridge

  19. GASTON(2004)

  20. Radar Overview PRE 3 PRE 1 PRE 2 Gaston Gaston 0000 UTC 040830 WSI NOWRAD Radar Mosaic 0000 UTC 040831 WSI NOWRAD Radar Mosaic

  21. Trough axis Ridge axis Developing PRE Gaston 2100 UTC30 Aug'04 2100 UTC 30 Aug'04 700 hPa h (dam) and WSI NOWRAD reflectivity (dBZ) 925 hPa h (dam), θe (K), and 200 hPa wind speed (m s-1) Maddox et al. (1979) Frontal Flash Flood Pattern

  22. Trough axis Ridge axis Developing PRE Gaston 2100 UTC30 Aug'04 2100 UTC 30 Aug'04 700 hPa h (dam) and WSI NOWRAD reflectivity (dBZ) 925 hPa h (dam), θe (K), and 200 hPa wind speed (m s-1) Maddox et al. (1979) Mesohigh Flash Flood Pattern

  23. PRE 2 Weak Low 1200 UTC 30 Aug 2004 a b SLP (hPa) and radar reflectivity (dBZ) Streamlines, q (g kg-1) and MFC (shaded  10-7 s-1) c  (K) and gradient (shaded every 2.5  10-5 K m-1)

  24. 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

  25. PRE 2 PRE 3 2100 UTC 30 Aug 2004 a b SLP (hPa) and radar reflectivity (dBZ) Streamlines, q (g kg-1) and MFC (shaded  10-7 s-1) c  (K) and gradient (shaded every 2.5  10-5 K m-1)

  26. 0000 UTC 30 Aug 2004 PRE 2 PRE 3 a b SLP (hPa) and radar reflectivity (dBZ) Streamlines, q (g kg-1) and MFC (shaded  10-7 s-1) c  (K) and gradient (shaded every 2.5  10-5 K m-1)

  27. 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

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

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

  30. CONCLUSIONS • ~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

  31. CONCLUSIONS Gaston (2004) case study illustrates that favored locations for PRE development are: • 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 • In areas of orographic uplift

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