The cone tells you where the center might go. The wind speed probabilities answer a more useful question: what are the odds that dangerous winds reach me? Once you can read them, they're one of the best tools for deciding whether to act.
What the product actually shows
NHC's wind-speed probabilities give the percent chance that sustained winds of a given strength will reach a location within the forecast period. There are three thresholds:
- 39 mph (tropical-storm-force) — strong enough to make outdoor prep dangerous and travel difficult.
- 58 mph — damaging winds.
- 74 mph (hurricane-force) — the threshold for serious structural danger.
The numbers are cumulative over the period (usually out to 5 days), so they give the overall odds that those winds arrive at some point — not at one exact hour.
Why the odds are rarely 100%
Every forecast carries uncertainty — in track, timing, and intensity. The probabilities fold all of that in. A 40% chance of tropical-storm-force winds is not “probably fine”: it's a serious, actionable risk, because the cost of being caught unprepared is high. Emergency managers routinely act on probabilities well below 50%.
How to use them
- Look up your location's number, not just whether you're “in the cone.” The probabilities cover a far wider area than the cone does.
- Watch the trend across advisories — rising odds mean it's time to finish preparing.
- Pair them with the wind-arrival-time graphic so you know not just if, but when to have everything done.
Bottom line
Wind probabilities turn an uncertain forecast into a number you can act on. Don't wait for certainty — a meaningful chance of tropical-storm-force wind is your cue to get ready, even if the cone's center is pointed somewhere else.