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HEAVY RAIN EVENTS PRECEDING THE ARRIVAL OF TROPICAL CYCLONES Matthew R. Cote, Lance F. Bosart, and 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 8 th Northeast Regional Operational Workshop 2 November 2006
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Observations - Predecessor rain events (PREs) form with some regularity well in advance of tropical cyclones (TCs) - Rainfall can be at least as significant as that directly associated with the TC Forecasting Issues - Most operational focus on track and intensity of the TC itself when PREs occur - Heavy rain in advance of the TC may increase flooding risks - Flooding may occur where it was otherwise not expected OVERVIEW AND MOTIVATION
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Demonstrate the PRE identification process Present preliminary climatological results Follow the evolution of the PREs associated with Katrina (29-30 August 2005) Compare the synoptic setup surrounding Katrina with that of the null case of Cindy (6-7 July 2005) GOALS
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IDENTIFYING PREs Coherent area of rain displaced downstream from the parent TC - NCDC and WSI NOWRAD radar imagery - NHC best-track data Normalized rainfall greater than 100 mm/day - NPVU QPE archive - NWS text products Diagnosis of important synoptic-scale features - NCEP/NARR gridded datasets
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PRE EXAMPLES OF PREs 1800 UTC 05829 WSI NOWRAD 2 km US Radar Mosaic
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EXAMPLES OF PREs PREs 0900 UTC 05830 WSI NOWRAD 2 km US Radar Mosaic
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CLIMATOLOGY Frequency Comparison of TC Occurrence with TCs Producing PREs 1979-2005
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CLIMATOLOGY TC Track vs. PRE Location 32 Cases 2004-2005
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Composition of Data Catalog - PRE 3 h positions based on rainfall centroid - TC positions and intensities during PREs - Approximate rainfall amounts isolated for each PRE Major PRE Characteristics - 12 TCs produced 32 PREs in 2004 and 2005 - Median Separation Distance: 987 km - Median Time Lag: 30 h - Median Event Duration: 12 h - Slow-moving TCs more likely to produce multiple PREs compared to those moving more quickly CLIMATOLOGY
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Heavy rainfall developed in association with: Mid- and upper-level jet- entrance region confluence zone Differential CVA caused by a weak short wave Moisture tongue extending through low-level ridge line Bosart and Carr (1978) conceptual model of antecedent rainfall PAST RESEARCH ON PRE WITH AGNES (1972)
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CASE STUDY: KATRINA (29-30 AUG 2005)
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1200 UTC 050829 925 hPa Ht (dam), Theta-e (K), and Winds (kts) 1200 UTC 050829 200 hPa Ht (dam) and Winds (kts) 1200 UTC 050829 700 hPa Ht (dam), AVor (10 -5 s -1 ), and 1000-500 hPa Thck (dam) 1200 UTC 050829 WSI NOWRAD 2 KM US Radar Mosaic
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1800 UTC 050829 925 hPa Ht (dam), Theta-e (K), and Winds (kts) 1800 UTC 050829 200 hPa Ht (dam) and Winds (kts) 1800 UTC 050829 700 hPa Ht (dam), AVor (10 -5 s -1 ), and 1000-500 hPa Thck (dam) 1800 UTC 050829 WSI NOWRAD 2 KM US Radar Mosaic
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0000 UTC 050830 925 hPa Ht (dam), Theta-e (K), and Winds (kts) 0000 UTC 050830 200 hPa Ht (dam) and Winds (kts) 0000 UTC 050830 700 hPa Ht (dam), AVor (10 -5 s -1 ), and 1000-500 hPa Thck (dam) 0000 UTC 050830 WSI NOWRAD 2 KM US Radar Mosaic
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0600 UTC 050830 925 hPa Ht (dam), Theta-e (K), and Winds (kts) 0600 UTC 050830 200 hPa Ht (dam) and Winds (kts) 0600 UTC 050830 700 hPa Ht (dam), AVor (10 -5 s -1 ), and 1000-500 hPa Thck (dam) 0600 UTC 050830 WSI NOWRAD 2 KM US Radar Mosaic
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1200 UTC 050830 925 hPa Ht (dam), Theta-e (K), and Winds (kts) 1200 UTC 050830 200 hPa Ht (dam) and Winds (kts) 1200 UTC 050830 700 hPa Ht (dam), AVor (10 -5 s -1 ), and 1000-500 hPa Thck (dam) 1200 UTC 050830 WSI NOWRAD 2 KM US Radar Mosaic
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1800 UTC 050830 925 hPa Ht (dam), Theta-e (K), and Winds (kts) 1800 UTC 050830 200 hPa Ht (dam) and Winds (kts) 1800 UTC 050830 700 hPa Ht (dam), AVor (10 -5 s -1 ), and 1000-500 hPa Thck (dam) 1800 UTC 050830 WSI NOWRAD 2 KM US Radar Mosaic
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NULL CASE: CINDY 6-7 July 2005
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1200 UTC 050706 925 hPa Ht (dam), Theta-e (K), and Winds (kts) 1200 UTC 050706 200 hPa Ht (dam) and Winds (kts) 1200 UTC 050706 700 hPa Ht (dam), AVor (10 -5 s -1 ), and 1000-500 hPa Thck (dam) 1200 UTC 050706 WSI NOWRAD 2 KM US Radar Mosaic
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1800 UTC 050706 925 hPa Ht (dam), Theta-e (K), and Winds (kts) 1800 UTC 050706 200 hPa Ht (dam) and Winds (kts) 1800 UTC 050706 700 hPa Ht (dam), AVor (10 -5 s -1 ), and 1000-500 hPa Thck (dam) 1800 UTC 050706 WSI NOWRAD 2 KM US Radar Mosaic
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0000 UTC 050707 925 hPa Ht (dam), Theta-e (K), and Winds (kts) 0000 UTC 050707 200 hPa Ht (dam) and Winds (kts) 0000 UTC 050707 700 hPa Ht (dam), AVor (10 -5 s -1 ), and 1000-500 hPa Thck (dam) 0000 UTC 050707 WSI NOWRAD 2 KM US Radar Mosaic
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0600 UTC 050707 925 hPa Ht (dam), Theta-e (K), and Winds (kts) 0600 UTC 050707 200 hPa Ht (dam) and Winds (kts) 0600 UTC 050707 700 hPa Ht (dam), AVor (10 -5 s -1 ), and 1000-500 hPa Thck (dam) 0600 UTC 050707 WSI NOWRAD 2 KM US Radar Mosaic
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1200 UTC 050707 925 hPa Ht (dam), Theta-e (K), and Winds (kts) 1200 UTC 050707 200 hPa Ht (dam) and Winds (kts) 1200 UTC 050707 700 hPa Ht (dam), AVor (10 -5 s -1 ), and 1000-500 hPa Thck (dam) 1200 UTC 050707 WSI NOWRAD 2 KM US Radar Mosaic
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CONCLUSIONS Katrina vs. Cindy Comparison - Bosart and Carr (1978) schematic model, coupled with separation distance, time lag, and TC speed statistics, may aid in predicting if, where, and how many PREs will develop - Longitude and orientation of trough axes appear important in determining potential PRE development Katrina Case Study - Weak forcing for ascent may be sufficient to trigger coherent areas of heavy rain downstream of approaching TCs - Positive θ e advection and divergent jet entrance and exit regions promote favorable conditions for heavy rain formation
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Expand PRE climatological data further back in time Provide adequate physical explanations for the differences between left-of-track, along-track, and right-of-track PREs, and the apparent left-of-track preference Examine the role mesoscale features may have played in the development of recent PREs Classify and subdivide the different modes of predecessor rain events FUTURE RESEARCH
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QUESTIONS? COMMENTS? mcote@atmos.albany.edu
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