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Tropical Cyclone Wind Speed Probability Products

Product Description Document

Wind speed probability products are designed to answer these questions:

  1. What are the chances of experiencing these winds?
  2. When is the event most likely to start?
  • Cumulative probabilities (0-12, 0-24, 0-36 etc) through 120 hours (5 days) indicate the overall likelihood that the event will occur sometime in the given time period.These can be stepped through incrementally or animated on the web pages.
  • Specific sustained wind speed thresholds available:
    • 34 knots (39 mph)Tropical Storm strength
    • 50 knots (58 mph)
    • 64 knots (74 mph)Hurricane strength

In the images below, there is a 20% chance of 34 kt winds on the Big Island and parts of Maui County through the next 108 hours. There is less than a 5% chance of 50 kt winds in the same time period. These probabilities will change with each updated forecast. They do not indicate the probability over the life time of the storm...only for the 120 hours covered by the current forecast.

Example of Prob 34
Example of Prob 50

What the numbers mean

  • Low probability numbers for extreme events are not insignificant.
  • 30% probability of experiencing 64 knot winds means a roughly 1 in 3 chance of hurricane conditions
  • The chance of having 34 knot winds (tropical storm conditions) will be much higher for the same storm

We welcome any and all feedback on these products. Please e-mail your comments to

The examples below show how these graphics will look during an actual forecast.

Wind at least 39 MPH (34 KTS)
Winds at least 58 MPH (50 KTS)
Winds at least 74 MPH (64 KTS)