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Rapid Intensification of Atlantic Tropical Cyclones

Rapid Intensification of Atlantic Tropical Cyclones. Briefing to the HFIP August 6, 2007. What is Rapid Intensification?. Kaplan and DeMaria (WF, 2003) 24 h increase in maximum sustained surface winds of at least 30 kt ~95 th percentile of intensity changes 1989-2000 sample

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Rapid Intensification of Atlantic Tropical Cyclones

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  1. Rapid Intensification of Atlantic Tropical Cyclones Briefing to the HFIP August 6, 2007

  2. What is Rapid Intensification? • Kaplan and DeMaria (WF, 2003) • 24 h increase in maximum sustained surface winds of at least 30 kt • ~95th percentile of intensity changes 1989-2000 sample • 83% of major hurricanes have at least one RI period • General environmental characteristics • Low vertical shear • Easterly 200 hPa flow • No upper level trough interaction • Moist lower troposphere • Sufficient MPI to support a 30 kt intensity increase

  3. Locations of RI Cases(from KD 2003)

  4. Additional Atlantic RI Statistics (1988-2006 Sample)

  5. Hit Rate, False Alarm Rate and False Alarm Ratiofor a Yes/No Event Forecast Yes No Yes Observed No h = # of yes forecasts that verified (hits) c = # of no forecasts that verified (correct non-events) f = # of yes forecasts that did not verify (false alarms) m = # of no forecasts where event occurred (missed) hit rate = h/(h+m) false alarm rate = f/(f+c) false alarm ratio = f/(f+h)

  6. Example: NHC Forecast of 24 hr Intensity Change of 25 kt or greater (90th percentile) Forecast Yes No Yes Observed No h = # of yes forecasts that verified (hits) c = # of no forecasts that verified (correct non-events) f = # of yes forecasts that did not verify (false alarms) m = # of no forecasts that where event occurred (missed) hit rate = h/(h+m) = 15.8% false alarm rate = f/(f+c) = 1.2% false alarm ratio = f/(f+h) = 41.5%

  7. 48 hr Decay Forecasts (dV ≤ -40 kt, 5th percentile)

  8. Sample Intensity Metrics • Reduce average 48 hour intensity error by 30% • 14.4 to 10 kt • Triple the hit rate of the 48 hour forecasts of rapid intensity (90th percentile) and halve the false alarm ratio • Hit Rate: 20 to 60 % (1/5 to 3/5) • False Alarm Ratio: 33 to 16% (1/3 to 1/6)

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