Interpreting Wind Speed Probability Products

Tropical cyclone wind speed probability products became operational at the National Hurricane Center (NHC) in 2006, following an experimental phase during 2004-05 that was supported by the Joint Hurricane Testbed (JHT). These NHC products include text and graphical versions that are updated with every forecast cycle for each active tropical cyclone in the Atlantic and eastern North Pacific basins. The probabilities are also being made available via the National Digital Forecast Database (NDFD). The products provide users with information regarding the chances of experiencing winds of tropical storm force and hurricane force at specific locations within the five-day forecast period. They also indicate, in probabilistic terms, the range of possibilities regarding when these wind conditions could begin at specific locations. The performance of these products during 2006 and 2007 will be examined, and a few changes to the products planned for 2008 will be highlighted. We will also summarize strategies for interpreting these products for use in effective risk communication. One of the significant challenges with the probabilities thus far has been relating them to coastal watches and warnings issued by the NHC. As part of a new JHT project, relationships between the probabilities and the placement of NHC coastal watches and warnings are being explored. One of the goals of the study is to evaluate the feasibility of using the probabilities to produce “first-guess” objective guidance on watch/warning issuance. Preliminary results of this evaluation will be presented.