Tropical Cyclone Wind Speed Probabilities Products

Contents

1. Overview
2. Description of the tropical cyclone wind speed probabilities text product
3. Description of the tropical cyclone wind speed probabilities graphical products
4. Description of the tropical cyclone NDFD wind speed probabilities products
5. Potential advantages as compared to previous products
6. Method for computing the wind speed probabilities

2. Description of the wind speed probabilities text product

The wind speed probabilities are provided in a storm-specific text product for selected coastal and inland cities along with each forecast issued by the NHC. Each wind speed probability text product provides probabilities (in percent) for wind speeds of at least 34 kt (39 mph, tropical storm force), 50 kt (58 mph), or 64 kt (74 mph, hurricane force) at each listed location. Two types of probability values are produced in this text product: cumulative probabilities of occurrence, and individual period probabilities of onset.

Cumulative probabilities are provided in the text product for the following time periods: 0-12 hours, 0-24 hours, 0-36 hours, 0-48 hours, 0-72 hours, 0-96 hours, and 0-120 hours (0-5 days). These cumulative probabilities indicate the overall chances that the stated wind speed will occur at each location during the period between hour 0 (the beginning of the forecast) and each listed forecast hour.

Individual period probabilities are provided for each of the following time intervals: 0-12 hours, 12-24 hours, 24-36 hours, 36-48 hours, 48-72 hours, 72-96 hours, and 96-120 hours. These individual period probabilities indicate the chances that the stated wind speed will start during each individual period at each location. Cumulative probabilities through each forecast time period are also just the sum of the individual period probabilities up to that time.

In other words, cumulative probabilities tell decision-makers the chances that the event will happen at all. The individual period probabilities tell decision-makers when the event is most likely to start.

View a complete example of the tropical cyclone wind speed probability text product.

Probabilities for a particular location and speed are provided only when the 120-hour (5-day) cumulative probability is at least 2.5% (rounded to 3%). Locations are listed in geographic order, and data for all wind speeds (with high enough probabilities) at one location are grouped together.

It is important for users to realize that probabilities that may seem relatively small may still be quite significant. The probabilities may indicate there is a chance that a damaging or even an extreme event may occur at your location. This may warrant making preparations to protect lives and property. Users are urged to consider the potentially immense cost (in terms of lives, property, etc.) of not preparing for an extreme event, even if the chances at an individual point are only perhaps 1 in 20 (5%) or 1 in 10 (10%) that the event will occur.

Next:  Description of the tropical cyclone wind speed probabilities graphical products