Tropical Cyclone Gale Wind Radii Estimates, Forecasts and Forecast Error Estimates for the Western North Pacific

The Joint Typhoon Warning Center recently extended forecasts of gale force and other wind radii to five days. That effort and a thrust to perform post-season analysis of gale force wind radii for the best tracks (the quality controlled and documented tropical cyclone track and intensity estimates released after the season) has prompted requirements for new guidance to address the challenges of both. An equally-weighted mean (i.e., a consensus) of gale force wind radii objective estimates used for real-time and post-season analysis was implemented in 2016, and has been updated to include estimates from scatterometer winds. A numerical weather prediction model consensus forecast for gale wind radii was also implemented in 2015 and has been updated to account for changes and improvements in numerical weather prediction forecast guidance. Assuming the consensus and subjective estimates are of equal quality, the uncertainty associated with estimating the extent of the gale-force winds are estimated to be approximately 15% of the mean or 18 n mi (33 km) for our sample. And finally, readily available real-time guidance (e.g., consensus spread, initial size, and forecast intensity) is used to estimate forecast error. These forecast error estimates are shown to perform as well or better than estimates for track and intensity errors done with the same methodology.