Surface Wind Speeds and Enthalpy Fluxes During Tropical Cyclone Formation From Easterly Waves: A CYGNSS View

We examined the Cyclone Global Navigation Satellite System (CYGNSS) retrievals of surface wind speeds and enthalpy fluxes in African easterly waves that led to the formation of 30 Atlantic tropical cyclones during 2018-2021. Lag composites show a cyclonic proto-vortex as early as 3 days prior to tropical cyclogenesis. The enthalpy flux distribution does not vary substantially before cyclogenesis, but subsequently, there is a marked increase in the extreme upper values. In the composites, a negative radial gradient of enthalpy fluxes becomes apparent 2-3 days before cyclogenesis. These results-based on novel data blending satellite retrievals and global reanalysis-support the findings from recent studies that the spin-up of tropical cyclones is associated with a shift of peak convection toward the vortex core and an inward increase of enthalpy fluxes.