A situation-dependent intensity and intensity spread prediction technique for the Atlantic called WAIA is developed using the same procedures as for our technique for the western North Pacific that is operational at the Joint Typhoon Warning Center. These simple techniques are based on rankings of the 10 best historical track analogs to match the official track forecast and current intensity. A key step is development of a bias correction to eliminate an over-forecast bias. The second key step is a calibration of the original intensity spread among the 10 analogs to achieve a probability of detection of about 68% at all forecast intervals, which we propose would be an appropriate intensity spread for the National Hurricane Center (NHC) official intensity forecasts.
The advantages of WAIA as an operational intensity forecast product for Atlantic tropical cyclones are described in terms of mean absolute errors, sample-mean biases, and geographic distributions of WAIA versus various guidance products available at NHC. Specific attention is given to the four guidance products that are included in the intensity consensus (ICON) technique that is the most skillful of all the products. Evidence is given that WAIA would be an independent, and more likely skillful at longer forecast intervals, technique to include in the ICON. Consequently, WAIA would likely lead to improved NHC intensity forecasts at four- to five-day intervals.