Impact of the North Atlantic Sea Surface Temperature Tripole on the Northwestern Pacific Weak Tropical Cyclone Frequency

Abstract

Abstract Previous studies focused on the intense TCs in the central-southeastern western North Pacific (WNP), whose variability is intimately linked to El Niño–Southern Oscillation and the extratropical sea surface temperature anomaly (SSTA) in the Pacific. Compared with them, weak TCs (WTCs) are more numerous and form farther northwestward. The great number of WTCs and thereby the landfall cases may also cause huge damage to countries in Southeast Asia. However, their modulators are far from fully understood. Our research emphasizes the delayed impact of the early spring North Atlantic tripole SSTA (NAT) on the WTC formation frequency through the “capacitor” effect of sea ice (SIC) and SST in the Barents Sea. Detailed analysis indicates that a positive NAT may modulate an anomalous high in the Barents Sea–North Europe and decrease the local low cloud cover. Thus, more downward solar radiation tends to heat the local SST and decrease the SIC. This warmer Barents Sea could maintain through the typhoon season and excite a significant southeastward wave train, with several centers in the Arctic, central Asia, and East Asia. The abnormal easterly wind to the south of the anticyclone in East Asia facilitates the cyclonic anomaly in the South China Sea, the Philippines, and the subtropical WNP, which reinforces the local monsoon trough and favors the WTC formation there. A physical-based empirical model is developed for the WTC frequency, and hindcast is performed from 1979 to 2018. It shows the early spring NAT effectively improves the prediction skill for the WTC frequency, which can be considered as a crucial source of predictability for WTCs. Significance Statement Previous studies have focused on the western North Pacific intense TCs. The great number of weak TCs (WTCs) and thereby the landfall cases may also cause huge damage. However, modulators for WTCs have not been fully understood. This research emphasizes the potential impact of the early spring North Atlantic tripole SSTA (NAT) pattern on the WTC frequency through the persistent sea ice and sea surface temperature in the Barents Sea. By considering the NAT signal, the seasonal forecasting skill for WTC frequency is effectively improved. Therefore, the NAT signal may help better understand the WTC variability about 1–2 seasons in advance.