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PREDECESSOR RAIN EVENTS IN ADVANCE OF TROPICAL CYCLONES

PREDECESSOR RAIN EVENTS IN ADVANCE OF TROPICAL CYCLONES. Matthew R. Cote, Lance F. Bosart, Daniel Keyser Department of Earth and Atmospheric Sciences University at Albany, SUNY, Albany, NY. Michael L. Jurewicz, Sr. National Weather Service Forecast Office Binghamton, NY.

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PREDECESSOR RAIN EVENTS IN ADVANCE OF TROPICAL CYCLONES

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  1. PREDECESSOR RAIN EVENTS IN ADVANCE OF TROPICAL CYCLONES Matthew R. Cote, Lance F. Bosart, Daniel Keyser Department of Earth and Atmospheric Sciences University at Albany, SUNY, Albany, NY Michael L. Jurewicz, Sr. National Weather Service Forecast Office Binghamton, NY CSTAR II Grant NA04NWS4680005 Master’s Thesis Seminar 5 July 2007

  2. MOTIVATION “…Map discussion focused on two heavy rain and flooding events in the Northeast that occurred well in advance of tropical systems (Katrina and Ophelia) in the past month.  These types of warm-season heavy rain events have been observed a number of times over the Northeast in advance of landfalling and transitioning tropical cyclones. They are often difficult to forecast and they constitute a significant operational research problem.” —Lance Bosart, in his synopsis of Friday Map Discussion, 16 Sep 2005

  3. RADAR DEPICTION OF KATRINA PREs PREs Katrina 0900 UTC 050830 WSI NOWRAD Reflectivity (dBZ)

  4. OUTLINE • Explain PRE identification process • Discuss related past research • Present statistical and composite climatology of PREs for 1998–2006 • Examine the synoptic-scale and mesoscale factors important in producing two PREs ahead of Gaston (2004) • Suggest methods for efficient technology transfer into NWS operations

  5. DATA SOURCES • NCDC and WSI NOWRAD radar imagery • NHC best-track data • NPVU QPE and NWS rainfall products • NCEP/NCAR 2.5° × 2.5° Reanalysis • NCEP/NARR 32-km 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

  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. PREVIOUS RESEARCH

  12. MADDOX ET AL. (1979): FLASH FLOOD PATTERNS SYNOPTIC PATTERN Greatest flash flood potential Greatest flash flood potential Midlevel Schematic Surface Schematic

  13. MADDOX ET AL. (1979): FLASH FLOOD PATTERNS FRONTAL PATTERN Greatest flash flood potential Greatest flash flood potential Midlevel Schematic Surface Schematic

  14. MADDOX ET AL. (1979): FLASH FLOOD PATTERNS MESOHIGH PATTERN Greatest flash flood potential Greatest flash flood potential Midlevel Schematic Surface Schematic

  15. BOSART AND CARR (1978): PRE AHEAD OF AGNES (1972) Conceptual model of antecedent rainfall

  16. PRE STATISTICS Separation Distance 1086 ± 482 km Median: 935 km Conceptual model of antecedent rainfall

  17. PRE STATISTICS Separation Distance 1086 ± 482 km Median: 935 km Event Duration 14 ± 7 h Median: 12 h Conceptual model of antecedent rainfall

  18. 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 Conceptual model of antecedent rainfall

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

  20. 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

  21. 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

  22. PRE TRACK-RELATIVE POSITIONS HIGH RAINFALL SLOWEST MOVEMENT

  23. PRE TRACK-RELATIVE POSITIONS HIGHEST RAINFALL PREs MOVE TWICE AS FAST

  24. SOUTHEAST RECURVATURE PRE COMPOSITES

  25. COMPOSITES: T-12 Trough axis Ridge axis θe-Ridge axis 700 hPa h (dam) and upward vertical motion (μb s-1) 925 hPa h (dam), θe (K), and 200 hPa wind speed (m s-1) Center of composite TC

  26. COMPOSITES: T0 Trough axis Ridge axis θe-Ridge axis 700 hPa h (dam) and upward vertical motion (μb s-1) 925 hPa h (dam), θe (K), and 200 hPa wind speed (m s-1) Center of composite TC Centroid of 1st composite PRE

  27. COMPOSITES: T+12 Ridge axis Trough axis θe-Ridge axis 700 hPa h (dam) and upward vertical motion (μb s-1) 925 hPa h (dam), θe (K), and 200 hPa wind speed (m s-1) Center of composite TC Centroid of 1st composite PRE Centroid of 2nd composite PRE

  28. Ridge axis Trough axis θe-Ridge axis T+12 T+12 700 hPa h (dam) and upward vertical motion (μb s-1) 925 hPa h (dam), θe (K), and 200 hPa wind speed (m s-1) Maddox et al. (1979) Synoptic Flash Flood Pattern

  29. GASTON (2004)

  30. GASTON (2004): TOTAL RAINFALL 1 Sep 1200 UTC positions 0000 UTC positions 31 Aug 30 Aug 28 Aug 29 Aug 72-h rainfall (mm) ending 1200 UTC 1 Sep 2004

  31. 1 Sep 24-h rainfall (mm) ending 1200 UTC 30 Aug 2004 24-h rainfall (mm) ending 1200 UTC 31 Aug 2004 1 Sep 1200 UTC positions 0000 UTC positions 31 Aug 30 Aug 28 Aug 29 Aug 24-h rainfall (mm) ending 1200 UTC 1 Sep 2004 72-h rainfall (mm) ending 1200 UTC 1 Sep 2004

  32. GASTON (2004): SYNOPTIC FEATURES Region A Trough axis Ridge axis Gaston 1200 UTC 040830 700 hPa h (dam) and WSI NOWRAD reflectivity (dBZ) 1200 UTC 040830 925 hPa h (dam), θe (K), and 200 hPa wind speed (m s−1)

  33. GASTON (2004): SYNOPTIC FEATURES Trough axis Ridge axis Developing PRE Gaston 2100 UTC 040830 700 hPa h (dam) and WSI NOWRAD reflectivity (dBZ) 2100 UTC 040830 925 hPa h (dam), θe (K), and 200 hPa wind speed (m s−1)

  34. Trough axis Ridge axis Developing PRE Gaston 2100 UTC 2100 UTC 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

  35. Trough axis Ridge axis Developing PRE Gaston 2100 UTC 2100 UTC 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

  36. CROSS SECTION: 1200 UTC 30 AUG 2004 UVM (μb s−1) θe (K) Relative Humidity (%) Frontogenesis [K (100 km)−1 (3 h)−1]

  37. CROSS SECTION: 2100 UTC 30 AUG 2004 Relative Humidity (%) Frontogenesis [K (100 km)−1 (3 h)−1]

  38. CLIMATOLOGY SUMMARY • ~1/3 of U.S. landfalling TCs produce at least one PRE, but landfall is not necessary • 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 • Composites of SE Recurvature PREs resemble Maddox et al. (1979) synoptic flash flood pattern

  39. 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

  40. 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

  41. TRANSFER OF PRE RESEARCH INTO OPERATIONS

  42. SUGGESTED FORECAST METHODOLOGY (1) Climatologically favored TC tracks and PRE locations

  43. SUGGESTED FORECAST METHODOLOGY (2) Conceptual models

  44. SUGGESTED FORECAST METHODOLOGY (3) Cross sections and soundings

  45. SUGGESTED FORECAST METHODOLOGY (4) 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

  46. SUGGESTED FORECAST METHODOLOGY (5) Post-event rainfall analysis

  47. SUGGESTIONS FOR FUTURE WORK • Apply “PV-thinking” to PRE cases • Perform modeling studies to assess PRE predictability and relative roles of different features • Construct composite soundings and calculate mean thermodynamic quantities • Develop methods for anticipating the mode of predecessor rain activity (i.e., organized or scattered, intense or weak, slow- or fast-moving)

  48. ACKNOWLEDGMENTS

  49. ACKNOWLEDGMENTS • Lance and Dan • Mike Jurewicz • Kevin and Dave • Celeste, Lynn, Sharon, and Patti • Anyone I may have forgotten!

  50. QUESTIONS? COMMENTS? mcote@atmos.albany.edu

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