Effect of Sea-Surface Temperature and Ambient Moisture on the Formation and Predictability of Tropical Cyclones Under Vertical Wind Shear: An Ensemble Predictability Perspective

The sensitivities of tropical cyclones (TC) rapid intensification (RI) predictability to the sea-surface temperature (SST) and ambient moisture under vertical wind shear are explored through a series of cloud-permitting ensemble simulations with small, random initial condition perturbations. On average, a higher SST has a positive effect on the TC formation and reduces the uncertainty of development for all shear conditions, while a drier environment has a negative impact on the TCs development and either broadens the ensemble spread of RI onset time or prevents the storm from forming when the shear-induced tilt is large. The sea surface temperature influence the predictability of RI through affecting the convection and diabatic heating release and hence the transition from the thermal energy to kinetic energy. The resulting vortices are much stronger in high SST ensemble, which benefits the precession to be much faster and the tilt to be noticeably smaller during precession. The role of the environmental dry air is weakening the convection by diluting the air moisture and forbidden or suppress the convection outside the moist envelop. The effect of dry air on the predictability is depending on the shear magnitude. The larger the shear, the bigger the influence of dry air on the spread of RI onset time.