Tropical Cyclone Track Forecasting - Length of Forecast Period

Length of Forecast Period

See also: History of Atlantic tropical cyclone warnings

Forecasts within hurricane advisories were issued one day into the future in 1954 before being extended to two days into the future in 1961, and three days into the future in 1964. Starting in the mid to late 1990s, research into tropical cyclones and how forecast models handle the systems led to substantial improvements in track error. By 2001, the error had reduced sufficiently to extend track out to 5 days in the future on public advisories. In addition, at 1700 UTC during the hurricane season, a medium range coordination call takes place between the Hydrometeorological Prediction Center and the National Hurricane Center to coordinate tropical cyclone placement on the medium range pressure forecasts 6 and 7 days into the future for the northeast Pacific and Atlantic basins. Every so often, even at this time range, successful predictions can be made.

In forecasts, the National Hurricane Center uses a track forecast cone for the graphical representation of the uncertainty in its forecasts of a tropical cyclone's future location. The cone represents the probable position of a tropical cyclone's circulation center, and is made by drawing a set of circles centered at each forecast point—12, 24, 36, 48, and 72 hours for a three-day forecast, as well as 96 and 120 hours for a five-day forecast. The radius of each circle is equal to encompass two-thirds of the historical official forecast errors for the preceding five-year period. The cone is then constructed by drawing a tangent line that connects the outside boundary of all the circles. The National Hurricane Center states that the entire track of the tropical cyclone "can be expected to remain within the cone roughly 60-70% of the time."