The North Equatorial Current and rapid intensification of super typhoons

Abstract

Super Typhoon Mangkhut, which traversed the North Equatorial Current (NEC; 8–17 °N) in the western North Pacific in 2018, was the most intense Category-5 tropical cyclone (TC) with the longest duration in history—3.5 days. Here we show that the combination of two factors—high ocean heat content (OHC) and increased stratification — makes the NEC region the most favored area for a rapid intensification (RI) of super typhoons, instead of the Eddy Rich Zone (17–25 °N), which was considered the most relevant for RI occurrence. The high OHC results from a northward deepening thermocline in geostrophic balance with the westward-flowing NEC. The stratification is derived from precipitation associated with the Inter-Tropical Convergence Zone in the summer peak typhoon season. These factors, which are increasingly significant over the past four decades, impede the TC-induced sea surface cooling, thus enhancing RI of TCs and simultaneously maintaining super typhoons over the NEC region.

Numerical Study of Effects of Warm Ocean Eddies on Tropical Cyclones Intensity in Northwest Pacific

“…For example, in Jebi and Kong-rey, the gradual intensification observed during the first day of simulations can be attributed to high OHC values along their respective tracks. These elevated OHC values, as observed in the North Equatorial Current (NEC) between 8 • N and 17 • N [51], reduce SST cooling, thus providing more heat energy for storm intensification. Despite the presence of high OHCs, the simulated rapid weakening of Trami is attributed to significant SST cooling caused by strong vertical mixing and upwelling underneath the storm due to its slow translation speed.…”