Graphical mapping of tropical cyclone forecast wind probabilities worldwide

The Tropical Storm Risk (TSR) new 'wind speed probability' graphical product is presented and described. This real-time product maps the likelihood that a specific point on a map will be struck by hurricane (74 mph) and/or by tropical storm strength (39mph) 1-min sustained winds over the next 5 days. The product is available for tropical storms worldwide and has been in routine operation since July 2005 at www.tropicalstormrisk.com.

The likelihood that winds of a given strength will occur are shown in colour-coded 5% bands from 1% to 100%. The wind speed probabilities are computed by modelling and combining the errors in the forecast track position with the errors in the forecast extent of winds in each storm quadrant. The modelling is performed separately for each forecast lead time. Errors are computed and modelled from the official forecast advisories issued in 2004. A latitude-longitude grid resolution of 0.2 x 0.2 degree (~22km) is employed throughout. The product is designed for clarity and utility and adds a new dimension to tropical storm tracking and risk assessment. Previously decision makers could only guess at the chance that a given location would be struck by damaging winds from an active tropical cyclone. This new quantitative tool allows users to see this likelihood at a glance out to 5 days lead. The product will help to reduce risk and uncertainty associated with active tropical storms worldwide.