These graphics show probabilities of sustained (1-minute average) surface wind speeds equal to or exceeding 34 kt…39 mph (tropical storm force). These wind speed probability graphics are based on the official National Hurricane Center (NHC) track, intensity, and wind radii forecasts, and on NHC forecast error statistics for those forecast variables during recent years. Each graphic provides cumulative probabilities that wind speeds of at least 39 mph will occur during cumulative time periods at each specific point on the map. The cumulative periods begin at the start of the forecast period and extend through the entire 5-day forecast period at cumulative 12-hour intervals (i.e., 0-12 h, 0-24 h, 0-36 h, … , 0-120 h). An individual graphic is produced for each cumulative interval, and the capability to zoom and animate through the periods is provided. To assess the overall risk of experiencing winds of at least 39 mph at any location, the 120-h graphics are recommended.
These probabilities will be updated by the NHC with each advisory package for all active tropical cyclones in the Atlantic and eastern North Pacific basins. While separate graphics are focused on each individual tropical cyclone, probabilities resulting from more than one active tropical cyclone may be seen on each graphic.
The previously provided strike probability product (discontinued after 2005) conveyed the chances of a “close” approach of the center of the cyclone. However, these new probability products are about the weather. That is, these cumulative wind speed probabilities provide the chances that wind speeds of at least 39 mph will occur at individual locations. The cumulative probabilities can answer the question, “What are the chances that sustained winds of tropical storm or hurricane force will occur at any specific location?” This can also help one answer the question, “Do I need to take certain actions to prepare?” A companion product, the wind speed probability text product, will also be issued and updated with each advisory package. That product is recommended to more easily assess when winds of each threshold are most likely to start at any specific location, helping to answer the question, “How long do I have to prepare?” Overall, these probabilities provide users with information that can enhance their ability to make preparedness decisions specific to their own situations.
It is important for users to realize that wind speed probabilities that might seem relatively small at their location might still be quite significant, since they indicate that there is a chance that a damaging or even extreme event could occur that warrants preparations to protect lives and property.