Impact Statements issued by the National Weather Service (NWS) New Orleans/Baton Rouge office, approximately one day prior to the landfall of Hurricane Katrina, proved to be invaluable in mobilizing many vulnerable residents of coastal Mississippi and Louisiana to take evasive, life-saving action. While these statements have been effective, until recently they had been based solely on deterministic forecast information. Adding probabilistic forecast data into the impact statement creation process provides a measure of confidence that is not readily apparent from deterministic information alone.

Recent projects have begun incorporating uncertainty into the creation of impact information for wind and freshwater (inland) flooding. The availability of probabilistic wind speed data from National Hurricane Center (NHC) forecasts now allows local NWS offices to use an improved method to create wind impacts, for tropical storms and low-grade hurricanes. In 2007, eight offices participated in an experiment, for which graphical and text impact information, based on this new method, was posted to the Internet. Results will be discussed, pending the outcome of the 2007 Hurricane Season.

The use of uncertainty information is expected to be applied to other primary tropical cyclone hazards, including freshwater (inland) flooding, storm surge inundation, and tornadoes, during the next several years. In 2007, local tests were conducted to evaluate a method which combined excessive rainfall probabilities from the Hydrometeorological Prediction Center, deterministic flood guidance from River Forecast Centers, and local quantitative precipitation forecasts, to produce impact information for inland flooding.

Experimental probabilities for NHC storm-specific surge height forecasts began in 2007, and plans are underway to incorporate these data into impact information, perhaps as early as the 2008 season. Other future initiatives may use higher wind speed thresholds to further tailor wind impact information, especially for levels at which significant structural damage occurs.

Future refinements of the impact creation process will continue to improve the confidence of those in the weather enterprise tasked with communicating impact from tropical cyclone-related hazards. Technological innovations, including increasing use of mobile Internet, applied geographical information systems, and shared databases of community and infrastructure, will allow impacts to be received and understood by a growing, diverse audience of decision makers and other users.