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Types of Hurricane Forecasts
Every hurricane forecast includes a prediction about the current storm's future position (track), the speed of its rotating winds (intensity), and the radius of its high winds (size) for the end of each pre-set forecast period (fixed time interval into the future). The standard forecast periods presently in use are as in the table. Some of them, notably the 36h and the 4- and 5-day forecasts, are of relatively recent vintage.
| 0h | current storm position (approximate) |
| 12h | 12-hour forecast |
| 24h | 1-day forecast |
| 36h | 36-hour forecast |
| 48h | 2-day forecast |
| 72h | 3-day forecast |
| 96h | 4-day forecast |
| 120h | 5-day forecast |
Track Forecast
The track forecast is the official prediction of the storm's position at the end of each forecast period, specified in degrees of latitude and longitude.
| Excerpts from Track Forecast for Tropical Storm Charley, August 10, 2004, 0900Z (5:00 a.m. EDT), through 72h |
|
....CENTER LOCATED NEAR 13.0N 66.3W AT 10/0900Z.... ....FORECAST VALID 10/1800Z 13.9N 69.3W.... ....FORECAST VALID 11/0600Z 15.0N 72.9W.... ....FORECAST VALID 11/1800Z 16.3N 76.2W.... ....FORECAST VALID 12/0600Z 17.5N 79.0W.... ....FORECAST VALID 13/0600Z 19.5N 82.5W.... |
Intensity Forecast
The intensity forecast is the official prediction of the maximum 1-minute sustained winds in the storm at the end of each forecast period, measured in nautical miles per hour (knots), or reduced to categories 1 through 5 on the Saffir-Simpson hurricane intensity scale. Also included is a current estimate of the barometric pressure, in millibars, at the center of the storm, but there is no forecast for central pressure.
| Excerpts from Intensity Forecast for Tropical Storm Charley, August 10, 2004, 0900Z (5:00 a.m. EDT), through 72h |
|
....ESTIMATED MINIMUM CENTRAL PRESSURE 1007 MB MAX SUSTAINED WINDS 35 KT WITH GUSTS TO 45 KT.... ....FORECAST VALID 10/1800Z....MAX WIND 40 KT...GUSTS 50 KT.... ....FORECAST VALID 11/0600Z....MAX WIND 45 KT...GUSTS 55 KT.... ....FORECAST VALID 11/1800Z....MAX WIND 50 KT...GUSTS 60 KT.... ....FORECAST VALID 12/0600Z....MAX WIND 55 KT...GUSTS 65 KT.... ....FORECAST VALID 13/0600Z....MAX WIND 65 KT...GUSTS 80 KT.... |
Size Forecast
The size forecast is the prediction about how far out from center the storm's most destructive winds might be encountered at the end of each forecast period up to 72h. It expressed in terms of radius, or distance from the eye, of winds surpassing each of several wind speed thresholds: hurricane-force, 50-knot (for mariners), and tropical storm-force.
| Excerpts from Size Forecast for Hurricane Rita (Forecast Advisory #20), September 22, 2005, 10:00 a.m. CDT |
|
....FORECAST VALID 23/0000Z.... ....64 KT... 75NE 75SE 50SW 75NW. 50 KT...100NE 90SE 70SW 100NW. 34 KT...170NE 150SE 110SW 170NW. WINDS ... VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.... |
These forecasts are skilled, though as with any other science, they are not perfect. Hurricane science includes procedures for quantifying the error in some of these forecasts (track and intensity), so that a margin of safety may be added by emergency managers and the public in fashioning their responses to approaching tropical weather systems. Error quantification may also be used to help ensure that the expectations the public has of the forecast are in harmony with the state of the science at any given time.
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