Seven-Day Intensity and Intensity Spread Predictions for Atlantic Tropical Cyclones

The extension of the Weighted Analog Intensity Atlantic (WAIA) prediction technique for Atlantic tropical cyclones (TCs) from 5 to 7 days revealed a need for two modifications. The first modification for the 7-dayWAIA was to randomly select 70% of the TCs in the entire 2000-15 sample to be the training set and use the remaining 30% as the independent set. The secondmodificationwas to ensure that appropriate analogs were selected for ending storm situations such as landfall, postrecurvature, and nondevelopment or delayed intensification within the 7-day forecast interval. By simply constraining the analog selection such that the intensity at the lastmatching point with the target TC track does not exceed 50 kt (where 1 kt50.51ms(-1)), an increasing overforecast bias with forecast interval was almost eliminated in both the training set and the independent set. With these two analog selectionmodifications, themean absolute errors, and the correlation coefficients of the 7-dayWAIA intensities with the verifying intensities, are essentially constant from 5 to 7 days, which establishes this WAIA as a viable technique for 7-day intensity forecasts of Atlantic TCs.