Extended Abstract (640K)2A.4
Prediction of August Atlantic basin hurricane activity
Eric Blake, Colorado State University, Fort Collins, CO
Though seasonal hurricane forecasts for the Atlantic basin have been a success, large gaps remain in understanding the strong month-to-month variability which occurs in many seasons. Otherwise active hurricane seasons can sometimes be very quiet in August while relatively inactive seasons can often be busy during this month. August TC activity is predicted by diagnosing large-scale climate features earlier in the year, utilizing the NCEP reanalysis data. It is shown that a substantial portion (55-70 percent) of the variance in August TC activity can be hindcast using a combination of twelve predictive global signals. The most prominent predictive factor is July 200 mb winds off the west coast of South America. When this wind is anomalously strong from the northeast, Atlantic TC activity is typically enhanced. Other July conditions associated with active Augusts include a weak subtropical high in the north Atlantic, an enhanced tropical high in the northwest Pacific, and low pressure in the Bering Sea region.
There are many potential uses of the August-only forecast. When it is used in combination with the Gray et al (1997) statistical forecast, the August forecast increases hindcast skill of the full season prediction by about ten percent. Forecast August NTC has a significant relationship with August TC landfall. August tropical-only hurricanes will be discussed in comparison with year-to-year differences in the rest of the season's activity.
Session 2A, Seasonal to Interannual Prediction and Predictability II (Parallel with Sessions 2B, 2C, & 2D)
Monday, 29 April 2002, 2:00 PM-3:30 PM
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