Improving the Forecasts of Wind and Wind Gusts in Tropical Cyclones for More Effective Hazard Communication

Tropical cyclones (TCs) pose a significant threat to life and property along the coastal regions of the United States. One of the primary hazards associated with TCs are their destructive winds and winds gusts. National Weather Service forecasters are tasked with creating local gridded forecasts of winds and wind gusts that are accurate, while also consistent with forecasts from the National Hurricane Center (NHC) and adjacent Weather Forecast Offices (WFOs). Forecasting winds and wind gusts in TC environments can be extremely challenging given difficulties with the track and intensity forecasts of the TC itself, the very localized nature of the wind field and its interaction with terrain and varying air masses, along with limitations in forecast production methodologies used at the WFOs. Regional wind and wind gust forecasts during several previous TCs have shown large non-meteorological inconsistencies across WFO boundaries and a positive sustained wind bias. These discrepancies complicate the interpretation of TC wind forecasts and the evaluation of the potential hazard. An accurate as well as a consistent forecast is required to effectively communicate the TC wind threat.

A recent Collaborative Science, Technology, and Applied Research project between North Carolina State University and several WFOs in the Southeast and Mid-Atlantic region aimed to improve the forecast of TC winds and wind gusts. By integrating and improving the science used at the WFOs as well as developing and updating tools and procedures used by forecasters in the production of the wind and wind gusts forecast, it was intended that both a scientifically-sound and more consistent TC wind forecast would result. Project collaborators developed a climatology of sustained wind speeds and wind gusts of recent TCs impacting the region. A systematic analysis of sustained wind speed forecasts for recent TCs impacting the study region was also completed. This information has been integrated into a forecast tool used by WFOs to initialize the NHC provided wind guidance. The tool now includes an improved vortex simulation of the wind field and a climatologically-based bias correction. In addition, WFOs now have the ability to use wind reduction factors and wind gust factors to more accurately and efficiently create and modify the winds and wind gusts across the forecast area while improving the collaboration process between WFOs. These improvements have been tested and refined at several WFOs in the Carolinas during the past few hurricane seasons. These new tools and the resulting improvements in the wind and wind gust forecast with Hurricane Arthur (2014) will be presented.