Influences of sea surface temperature in the tropical Pacific and Indian Oceans on tropical cyclone genesis over the western North Pacific in May

This study investigated the effects of sea surface temperature (SST) in different tropical regions on tropical cyclone (TC) genesis over the western North Pacific (WNP) in May. The results revealed that positive SST anomalies over the tropical Pacific (Indian) Ocean in March may lead to increased (decreased) numbers of TCs over the WNP in May by affecting the atmospheric circulation anomalies over the WNP. Warmer SSTs over the tropical Pacific Ocean (TPO) may lead to stronger low-level southwesterly winds and enhanced convection. However, warmer SSTs over the tropical Indian Ocean (TIO) may enhance the western part of the western Pacific subtropical high (WPSH) and suppress convection. Further analysis suggests that changes in the atmospheric circulation anomalies over the WNP are related to changes in environmental factors. Concomitantly with the positive SST anomalies over the TPO, a favorable environment for TC genesis in May is present, with stronger low-level relative vorticity and upper-level divergence, smaller vertical wind shear and abundant water vapor. In contrast, the positive SST anomalies over the TIO might lead to an unfavorable environment for TC genesis over the WNP. This study also investigated the joint contributions of the TPO and TIO, and the results indicate that positive SST anomalies over the TPO and negative SST anomalies over the TIO may lead to an increased number of TC geneses. The analysis of the energy budget suggests that the joint activity of the TPO and TIO influences the barotropic eddy kinetic energy conversions and is mainly attributed to the contributions from the meridional shear of the mean zonal winds and the zonal wind convergence.