Experimental Tropical Cyclone Surface Wind Speed Probabilities

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Contents

1. Overview
2. Description of the wind speed probabilities graphical products
3. Potential advantages as compared to existing products
4. Method for computing the Wind Speed Probabilities

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4. Method for computing the Wind Speed Probabilities

The calculation of the wind speed probabilities is accomplished by creating a large set of alternate but plausible tracks and intensities roughly centered around the current official forecast. These alternate forecasts are determined by random sampling of historical track and intensity errors in official NHC forecasts (since 2001). The alternate intensity forecasts consider whether each alternate track is over land or water and corrects the alternate intensity forecast accordingly. The size of the tropical cyclone (set of wind radii) for each alternate track is determined by a climatology and persistence (CLIPER) model and its error components. An adjustment is made so that the wind radii represent the average, rather than the maximum, extent of winds in each quadrant. This results in probabilities of actually experiencing wind speeds, not probabilities of falling within the forecast wind radii. Swaths of particular wind speeds are then computed for each realization. Probabilities are computed on a 0.5x0.5 degree latitude-longitude grid by counting the fraction of realizations in which each point falls within a given wind swath (34, 50, or 64 kt). This output is then processed and expressed in text or graphical format via the experimental products being produced by the NHC during 2005.

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