Violent typhoons continue to have catastrophic impacts on economies and welfare, but how they are responding to global warming has yet to be fully understood. Here, an empirical framework is used to explain physically why observations support a tight connection between increasing ocean warmth and the increasing intensity of supertyphoons in the western North Pacific. It is shown that the energy needed for deep convection is on the rise with greater heat and moisture in the lower tropical troposphere but that this energy remains untapped when air pressure is high. Accordingly, tropical cyclone formation is becoming less common, but those that do form are likely to reach extreme intensities from the discharge of stored energy. These thermodynamic changes to the environment most significantly influence the upper portion of extreme typhoon intensities, indicating that supertyphoons are likely to be stronger at the expense of overall tropical cyclone occurrences in the western North Pacific.

Characteristics of marine heatwaves (MHWs) in the East Asian Marginal Seas (EAMS) were investigated using the daily Optimum Interpolation Sea Surface Temperature for 37 years (1982–2018), focusing on seasonal changes and regional differences. The summer MHWs occur 54% more frequently (2.7 events/decade) in a relatively wide area than in other seasons. The strong (up to 3.7 °C) and long-lasting (up to 38 days/event) winter MHWs are concentrated along the subpolar front (SPF) in the East/Japan Sea (EJS) where the MHWs are 20% longer (2.2 days/event) than in the Yellow and East China Seas (YECS). The summer MHWs are primarily driven by increased shortwave radiation associated with reduced cloud cover and latent cooling from the weakened wind over the western flank of developing subtropical highs. Driving mechanisms of the winter MHWs differ by region. The YECS MHWs occur mainly due to the atmospheric processes associated with weakening continental highs, while the EJS MHWs are largely driven by the northward shift of the SPF. Although large-scale atmospheric processes primarily drive the summer MHWs occurring in a wide area in the EAMS, our findings suggest that ocean processes can be major contributors to intensified MHW generation in limited areas, especially in winter.

Western North Pacific tropical cyclone (TC) activity is known to have a significant response to El Niño and Southern Oscillation (ENSO). Among the TC intensity classifications, “super typhoon”, is widely used as a symbolic word for warning people about the potential for experiencing the most severe typhoon. This study quantifies the contribution of super typhoons to TC activity in response to ENSO, where the Southern Oscillation Index (SOI) is used to indicate the internal variation of ENSO. It is found that the number and the genesis location of non-super typhoons are little influenced by ENSO, and the changes are mostly by the addition of super typhoons. Historical levels of El Niño and La Niña span from −2σ to +2σ of the SOI. Over this range of SOI values, the mean response is 5.6 super typhoons (7.1 for El Niño and 1.5 for La Niña) which nearly matches the mean response overall of 6 storms (24.6 for El Niño and 18.6 for La Niña). The spatial distribution of TC genesis locations for different ENSO conditions does not completely explain these results.

The climate of 2015 was characterized by a strong El Niño, global warmth, and record-setting tropical cyclone (TC) intensity for western North Pacific typhoons. In this study, the highest TC intensity in 32 years (1984–2015) is shown to be a consequence of above normal TC activity—following natural internal variation—and greater efficiency of intensity. The efficiency of intensity (EINT) is termed the “blasting” effect and refers to typhoon intensification at the expense of occurrence. Statistical models show that the EINT is mostly due to the anomalous warmth in the environment indicated by global mean sea surface temperature. In comparison, the EINT due to El Niño is negligible. This implies that the record-setting intensity of 2015 might not have occurred without environmental warming and suggests that a year with even greater TC intensity is possible in the near future when above normal activity coincides with another record EINT due to continued multidecadal warming.

This study introduces an unequally weighted technique for Multi-model Ensemble (MME) forecasting for western North Pacific Tropical Cyclone (TC) tracks. Weights are calculated by partial least square regression, and members are selected by paired t-test. The performances for shorter forecast time ranges, such as 24, 48 and 72 h, are examined in order to improve the MME model, in which the weights for members are equally assigned. For longer forecast time ranges, such as 96 and 120 h, weights for MME members are thought to be less reliable, since the modeling is more likely to be influenced by the climate variability in the data period. A combination of both techniques for the shorter and the longer forecast time ranges is suggested as an alternative MME forecast procedure in operational meteorological agencies.