Coherent variations of tropical cyclogenesis over the North Pacific and North Atlantic

The present study investigates the relationship of tropical cyclone (TC) genesis among the western North Pacific (WNP), eastern North Pacific (ENP), and tropical North Atlantic Ocean (TNA) during July-October (JASO) from 1979 to 2019. A coherent interannual variation is found for TC genesis among the southeastern part of the WNP (SEW for brevity), ENP and TNA. When there are more TCs generated over the SEW, TC geneses are more than normal over the ENP, but less than normal over the TNA. Correlation analysis shows there is a significant positive (negative) relationship between the SEW/ENP (TNA) TC genesis and a tripole zonal sea surface temperatures (SST) anomaly distribution among the central and eastern Pacific Ocean, western Pacific and tropical Atlantic Ocean. The zonal tripole SST anomalies provide favorable genesis potential index (GPI) anomalies for TC genesis over the SEW and ENP, but unfavorable GPI anomalies over the TNA. The diagnoses display that the absolute vorticity has the greatest contribution and the contributions of the relative humidity and vertical wind shear terms are secondary to GPI anomalies over the SEW. The positive GPI anomalies are mainly due to a positive contribution of the vertical wind shear and potential intensity over the ENP. The major term contributing to the negative GPI anomalies is the vertical wind shear over the TNA. This study may help to improve seasonal prediction of the TC genesis over the WNP, ENP and TNA.