Improvements in Tropical Cyclone Track Forecasting in the Atlantic Basin, 1970–98

Abstract

Tropical cyclone track forecasts issued by the Tropical Prediction Center/National Hurricane Center for the Atlantic basin have improved over the period 1970?98. Improvement is shown at 24, 48, and 72 h. Although this improvement can be shown without any preconditioning of the data, the question of accounting for forecast difficulty is addressed, building upon the work of Neumann. A decrease in the initial position errors over the same period is also shown. Track forecast errors generated by the Atlantic climatology and persistence (CLIPER) model (run in "best?track" mode) are used as a measure of forecast difficulty. Using the annual average CLIPER errors in a regression against the official forecast errors yields an equation giving an expected error for each year under consideration. The expected error (representing forecast difficulty) is then subtracted from the observed official errors. The resulting set of differences can then be examined for long?term trends, difficulty having been accounted for. Fitting a straight line to these differences (1970?98) yields the result that official forecast errors have decreased by an average of 1.0% per year at 24 h, by 1.7% per year at 48 h, and by 1.9% per year at 72 h. A second?order fit, however, suggests that the rate of improvement has increased during the latter half of the period.