Heavy rainfall associated with land-falling tropical cyclones is a common contributor to major inland flooding events, which can be far removed from the initial coastal threats of storm surge and extreme winds. In fact, inland flooding was responsible for more than half of the deaths associated with tropical cyclones in the United States during the period 1971-2000. This statistic suggests a need for improved quality and lead-times in such precipitation and river flood forecasts. Unfortunately, accurately forecasting the location and amount of precipitation associated with tropical cyclones is dependent on a multitude of factors, including synoptic scale forcing mechanisms, mesoscale processes, topography, and model performance. Due to these limitations on forecast skill, a historical database of storm total precipitation can provide useful guidance to operational forecasters during the preparation of emergency preparedness statements, watches, and warnings.

As a joint project between the Lower Mississippi River Forecast Center and the Southeast Regional Climate Center, a tropical cyclone precipitation climatology was created using rainfall data from tropical storms and hurricanes that impacted the southeastern United States from 1971-2000. Using the Spatial Analyst tool in ArcView*, an inverse distance weighting technique was used to produce a graphical representation of storm total precipitation for 77 storms. Data from each storm analysis were exported to an ASCII grid format and mean areal precipitation statistics were computed using grid cell averages within each basin for the Southern Region River Forecast Centers. The storm total precipitation data are currently available through an Intranet site developed by the River Forecast Center and the Regional Climate Center.

The purpose of this project was to provide guidance to the River Forecast Centers for quantitative precipitation and contingency forecasting for impending tropical cyclones. By utilizing the historical values as guidance for the NWS River Forecast System, lead-times and forecast skill for inland flood events should improve. Future work will expand the historical precipitation database to include all land-falling tropical cyclones from the Atlantic Basin with the addition of states in the Midwest, Northeast, and Mid-Atlantic regions. Additional research may investigate the application of the method to individual inland flooding events to test the skill of climatology relative to current operational forecasting tools.

* Mention of a commercial product does not constitute an endorsement or recommendation by the National Weather Service or any of its field offices or employees.