Supertyphoon Megi (2010) left behind two very contrasting SST cold-wake cooling patterns between the Philippine Sea (1.5°C) and the South China Sea (7°C). Based on various radii of radial winds, the authors found that the size of Megi doubles over the South China Sea when it curves northward. On average, the radius of maximum wind (RMW) increased from 18.8 km over the Philippine Sea to 43.1 km over the South China Sea; the radius of 64-kt (33 m s⁻¹) typhoon-force wind (R64) increased from 52.6 to 119.7 km; the radius of 50-kt (25.7 m s⁻¹) damaging-force wind (R50) increased from 91.8 to 210 km; and the radius of 34-kt (17.5 m s⁻¹) gale-force wind (R34) increased from 162.3 to 358.5 km. To investigate the typhoon size effect, the authors conduct a series of numerical experiments on Megi-induced SST cooling by keeping other factors unchanged, that is, typhoon translation speed and ocean subsurface thermal structure. The results show that if it were not for Megi’s size increase over the South China Sea, the during-Megi SST cooling magnitude would have been 52% less (reduced from 4° to 1.9°C), the right bias in cooling would have been 60% (or 30 km) less, and the width of the cooling would have been 61% (or 52 km) less, suggesting that typhoon size is as important as other well-known factors on SST cooling. Aside from the size effect, the authors also conduct a straight-track experiment and find that the curvature of Megi contributes up to 30% (or 1.2°C) of cooling over the South China Sea.

On 23 August, 2017, Typhoon Hato rapidly intensified by 10 kt within 3 h just prior to landfall in the city of Macau along the South China coast. Hato’s surface winds in excess of 50 m s⁻¹ devastated the city, causing unprecedented damage and social impact. This study reveals that anomalously warm ocean conditions in the nearshore shallow water (depth < 30 m) likely played a key role in Hato’s fast intensification. In particular, cooling of the sea surface temperature (SST) generated by Hato at the critical landfall point was estimated to be only 0.1–0.5 °C. The results from both a simple ocean mixing scheme and full dynamical ocean model indicate that SST cooling was minimized in the shallow coastal waters due to a lack of cool water at depth. Given the nearly invariant SST in the coastal waters, we estimate a large amount of heat flux, i.e., 1.9k W m⁻², during the landfall period. Experiments indicate that in the absence of shallow bathymetry, and thus, if nominal cool water had been available for vertical mixing, the SST cooling would have been enhanced from 0.1 °C to 1.4 °C, and sea to air heat flux reduced by about a quarter. Numerical simulations with an atmospheric model suggest that the intensity of Hato was very sensitive to air-sea heat flux in the coastal region, indicating the critical importance of coastal ocean hydrography.

Tropical Cyclones (TCs) are devastating natural disasters. Analyzing four decades of global TC data, here we find that among all global TC-active basins, the South China Sea (SCS) stands out as particularly difficult ocean for TCs to intensify, despite favorable atmosphere and ocean conditions. Over the SCS, TC intensification rate and its probability for a rapid intensification (intensification by ≥ 15.4 m s⁻¹ day⁻¹) are only 1/2 and 1/3, respectively, of those for the rest of the world ocean. Originating from complex interplays between astronomic tides and the SCS topography, gigantic ocean internal tides interact with TC-generated oceanic near-inertial waves and induce a strong ocean cooling effect, suppressing the TC intensification. Inclusion of this interaction between internal tides and TC in operational weather prediction systems is expected to improve forecast of TC intensity in the SCS and in other regions where strong internal tides are present.

Due to the cold water temperatures, the East China Sea (ECS) is usually unfavorable for typhoon development. Recently, in a rare event, Typhoon Bavi (2020) reached major typhoon status and became the strongest typhoon in the ECS in the past decade. Based on in situ observations and model simulations, we discover that this typhoon is fueled by a marine heatwave, which creates a very warm ocean condition with sea surface temperature (SST) exceeding 30 °C. Also, because of suppressed typhoon-induced SST cooling caused by the shallow water depth (41 m) and strong salinity stratification (river runoff) within the ECS, the SST beneath the typhoon remains relatively high and enhances the total heat flux for the typhoon. More interestingly, due to the fair weather ahead of the typhoon, we find that the rapid development of this marine heatwave is likely, in part, attributed to the typhoon itself. As the risks from typhoons and marine heatwaves are heightening under climate change, this study provides important insights into the interaction between typhoons and marine heatwaves.

The sea surface temperature (SST) beneath a tropical cyclone (TC) is of great importance to its dynamics; therefore, understanding and accurately estimating the magnitude of SST cooling is of vital importance. Existing studies have explored important influences on SST of TC translation speed, maximum surface winds, ocean thermal condition, and ocean stratification. But the influence of the TC wind radii (or collectively called the TC size) on SST has been largely overlooked. In this study, we assess the influence of wind radii uncertainty on SST cooling by a total of 15,983 numerical simulations for the western North Pacific during the 2014–2018 seasons. Results show a 6%–20% SST cooling error induced using wind radii from the Joint Typhoon Warning Center official forecast and a 35%–40% SST cooling error using wind radii from the operational runs of the Hurricane Weather Research and Forecasting (HWRF) model. Our results indicate that SST cooling is most sensitive to the radius of 64 kt winds (R64) due to its effects on the integrated kinetic energy of the TC and subsequent mixing of the ocean surface layer. It is also found that the correlation between SST cooling induced by the TC and its size is 0.49, which is the highest among all the parameters tested. This suggests that it is extremely important to get TC size correct in order to predict the SST cooling response, which then impacts TC evolution in numerical weather prediction models.

Hurricane Patricia formed on 20 October 2015 in the Eastern Pacific and, in less than 3 days, rapidly intensified from a Tropical Storm to a record‐breaking hurricane with maximum sustained winds measured around 185 knots. It is almost 15 knots higher than 2013's supertyphoon Haiyan (the previous strongest tropical cyclone (TC) ever observed). This research focuses on analyzing the air‐sea enthalpy flux conditions that contributed to Hurricane Patricia's rapid intensification, and comparing them to supertyphoon Haiyan's. Despite a stronger cooling effect, a higher enthalpy flux supply is found during Patricia, in particular due to warmer pre‐TC sea surface temperature conditions. This resulted in larger temperature and humidity differences at the air‐sea interface, contributing to larger air‐sea enthalpy heat fluxes available for Patricia's growth (24% more than for Haiyan). In addition, air‐sea fluxes simulations were performed for Hurricane Patricia under different climate conditions to assess specifically the impact of local and large‐scale conditions on storm intensification associated with six different phases and types of El Niño Southern Oscillation (ENSO) and long‐term climatological summer condition. We found that the Eastern Pacific El Niño developing and decaying summers, and the Central Pacific El Niño developing summer are the three most favorable ENSO conditions for storm intensification. This still represents a 37% smaller flux supply than in October 2015, suggesting that Patricia extraordinary growth is not achievable under any of these typical ENSO conditions but rather the result of the exceptional environmental conditions associated with the buildup of the strongest El Niño ever recorded.