Intensified Mega-ENSO Has Increased the Proportion of Intense Tropical Cyclones Over the Western Northwest Pacific Since the Late 1970s

Intense tropical cyclones (TCs) formed over the western part of the western North Pacific (WWNP) pose greater coastal risk than those formed over the eastern part (EWNP). Here we show that the proportion of intense TCs relative to all TCs (PITC) locally formed over the WWNP west of 140 degrees E has increased significantly by about 16% to 20%, or equivalently almost doubled, since the late 1970s. However, the PITC over the EWNP has experienced little change. This sharp west-east contrast is primarily driven by the La Nina-like sea surface temperature (SST) pattern in the Pacific, identified as the mega El Nino-Southern Oscillation (ENSO) in previous studies. It is shown that the strong warming in the WWNP has contributed greatly to the increased PITC. In the EWNP, the dynamical conditions associated with the intensified mega-ENSO play a vital opposite role in offsetting and even overweighting the effect of local SST warming. Plain Language Summary Intense tropical cyclones (TCs) formed over the western part of the western North Pacific (WWNP) pose greater coastal risk than those formed over the eastern part (EWNP). Here we show that the proportion of intense TCs relative to all TCs (PITC) locally formed over the WWNP west of 140 degrees E has almost doubled since the late 1970s. However, the PITC over the EWNP has experienced little change. This sharp west-east contrast is primarily driven by the La Nina-like sea surface temperature (SST) pattern in the Pacific, identified as the mega El Nino-Southern Oscillation (ENSO) in previous studies. The strong warming in the WWNP has contributed greatly to the increased PITC, while the dynamical conditions associated with the intensified mega-ENSO play a vital opposite role in offsetting and even overweighting the effect of local SST warming over the EWNP.