Composite Analysis of Environmental Conditions for GEFS-based Tropical Cyclone Genesis Hits and False Alarms in the JTWC Region

This presentation reviews the results of generating 15°x15° composites of objectively determined Tropical Cyclone (TC) genesis events using the control member of the Global Ensemble Forecast System (GEFS) from September 2020 to December 2023. Hit and false alarm events are identified using a methodology based on Halperin et al. (2017), with cases further separated into subbasins as defined by Cowan (2022). Differences in hit and false alarm composites for each subbasin are computed, and the statistical significance of differences at each individual 0.50° grid point are calculated using the Mann-Whitney U-test at the 95th, 97th, and 99th percentiles.

By examining the resulting composites and composite differences in the GEFS-based TC genesis cases, we aim to identify key environmental regions that differentiate successful genesis forecasts (hits) from incorrect predictions (false alarms) based on the objective genesis thresholds. The findings are intended to provide operational forecasters with insights into spatial regions of statistically significant differences. We then assess whether these spatial differences are substantial enough to interpret potential genesis events within the GEFS differently.