IMPROVING SEASONAL HURRICANE PREDICTIONS FOR THE ATLANTIC BASIN

This paper demonstrates that improved forecasts of the annual number o f hurricanes in the Atlantic tropical basin are possible by separating tropical-only hurricanes from hurricanes influenced by extratropical factors. It is revealed that variables previously shown to have a pred ictive relationship with the annual number of Atlantic hurricanes have a significantly stronger predictive association with the number of hu rricanes formed solely from tropical mechanisms. This stronger relatio nship exists for extended-range (6-month lead) as well as for short-ra nge (0-month lead) forecast models. Any future study of seasonal hurri cane activity over this region should consider tropical-only hurricane s as separate from hurricanes influenced by baroclinic disturbances. T he annual number of hurricanes that form or intensify as a result of i nteractions with baroclinic disturbances appears unrelated to signific ant tropical or midlatitude atmospheric anomalies and thus should be c onsidered the random component of seasonal hurricane activity, at leas t until further insights are gained. Indeed, when prediction algorithm s are developed to forecast the annual number of Atlantic hurricanes, best hindcast skill results from models that assume a simple average f or baroclinically influenced storms. These regression-based forecast m odels are only marginally better than climatology.