A Statistical and Numerical Modeling Approach to Improved Landfalling Tropical Cyclone Wind Forecasts

Tropical meteorologists and operational forecasters continue to be challenged with the development of accurate forecasts of hazardous weather associated with landfalling tropical cyclones. Forecasts of inland sustained wind speed and peak gust values are some of the areas with greatest opportunity for improvement. There have been numerous past studies that have examined the evolution of the tropical cyclone wind field when transitioning from a marine to continental environment. However, very few of the results from these studies have been used in operations. The National Hurricane Center's (NHC) currently supplies Weather Forecasting Offices (WFOs) with quadrant-based maximum wind radii forecasts available at twelve hourly temporal resolution. A tool available to the WFOs interpolates the relatively coarse wind radii forecasts to a 5 km x 5 km hourly grid. Forecasters are then tasked with modifying this output. A recent survey of local WFOs in the Mid-Atlantic and Southeast indicated many forecasters find the modification process quite subjective. Forecasters indicate that adjustments are often made without strong scientific backing, leading to strong discontinuities in forecasts from neighboring WFOs.

The purpose of this study is to improve the wind speed and wind gust forecasts associated with landfalling tropical cyclones. The primary focuses of the research are in the improvement of land decay and gust factors applied in the TCMWindTool used by WFOs. A climatology of observed sustained wind speed distributions has been developed for various locations in the region and is compared to distributions associated with landfalling tropical cyclones. Wind speed decay as a system moves over land has also been examined for recent tropical cyclones in the area. Forecasts from the National Digital Forecast Database were compared to station observations as well as the Hurricane Research Division H*Wind products in order to get a sense of the forecast bias for recent past landfalling tropical cyclones. A series of high-resolution idealized modeling studies have been developed to provide a dynamical foundation for the sustained wind speed and gusts for various locations in the region. The final product from the study will be a statistical-dynamical model that local WFOs can use to provide a scientific foundation for land decay and gust factors applied to the coarse input provided by the NHC.