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34-knot Wind Speed Probability
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Experimental Arrival Time of Tropical-Storm-Force Winds

Arrival Time of TS Winds 5-day Windspeed Probabilities



time of arrival graphic

About this product:

The prototype timing graphics are created using the same Monte Carlo wind speed probability model that is currently used to determine the risk of tropical-storm- and hurricane-force winds at individual locations – a model in which 1000 plausible scenarios are constructed using the official NHC tropical cyclone forecast and its historical errors. Additional information on this product and the underlying technique is available on the NHC website.

There will be two versions of the experimental Arrival of Tropical-Storm-Force Winds Graphic available on the NHC website for all tropical cyclones, post-tropical cyclones, and potential tropical cyclones for which NHC is issuing advisories:

  1. Earliest Reasonable Arrival Time: the primary graphic, which identifies the time window that users at individual locations can safely assume will be free from tropical-storm-force winds. Specifically, this is the time before which there is no more than a 1-in-10 (10 percent) chance of seeing the onset of sustained tropical-storm-force winds – the period during which preparations should ideally be completed for those with a low tolerance for risk.

  2. Most Likely Arrival Time: the graphic that identifies the time before or after which the onset of tropical-storm-force winds is equally likely. This graphic would be more appropriate for users who are willing to risk not having completed all their preparations before the storm arrives.

Timing information will only be available for locations that have at least a 5 percent chance of experiencing sustained tropical-storm-force winds during the next 5 days.

Each of these versions will also be available overlaid on top of the cumulative 5-day probability of tropical-storm-force winds, providing a single combined depiction of the likelihood of tropical-storm-force winds at individual locations, along with their possible or likely arrival times.

The graphics will be updated with each new NHC full advisory package. Arrival times will be depicted with higher temporal resolution (i.e., in 6-hour intervals) during the first day of the 5-day forecast, increasing to lower temporal resolution (i.e., in 12-hour intervals) after the first day of the 5-day forecast period. Arrival times will be referenced to 8 AM and 8 PM local time, using a constant time zone that corresponds to where the cyclone is located at the time of the advisory. For example, if a cyclone is located in the Eastern Time Zone at the time of an advisory but is forecast to move into the Central Time Zone during the 5-day forecast period, all times on the graphic will be referenced to the Eastern Time Zone.

Considering the combined forecast uncertainties in track, intensity, and size, the chances that any particular location will experience winds of 34 kt (tropical storm force), 50 kt, or 64 kt (hurricane force) from this tropical cyclone are presented in tabular form for selected locations and forecast positions. This information is also presented in graphical form for the 34 kt, 50 kt, and 64 kt thresholds.

Note:  This information is also available in PDF format.