Chapter 4 One of the most challenging problems of tropical cyclone forecasting has been that of accurately determining whether or not a tropical cyclone will recurve into the mid-latitude westerlies and, if so, when. When a tropical cyclone is forecast to recurve and does not, or when forecast to not recurve and does, the resulting errors can be very large, often exceeding 200 nm (nautical mile) at 24 hours, 400 nm at 48 hours, and 800 nm at 72 hours. Large errors can be costly, both in lives and dollars, and also expand the range of errors, causing the average error to be higher than the most frequently occurring (modal) error and less meaningful to operational decision making.
Most evacuation decisions must be made 36 to 48 hours prior to the anticipated arrival of destructive winds, or winds that would prevent ship sorties or aircraft evacuations. Unnecessary aircraft evacuations, ship storm-evasions, and local destructive wind preparations can amount to hundreds of thousands of needlessly spent dollars. Poor forecasts lower the operational user's confidence in subsequent warnings, and reduce the overall effectiveness of the tropical cyclone warning system (Guard, 1977).
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Chapter 4
Section 1