Rapid deepening of tropical cyclones in the northeastern Tropical Pacific: The relationship with ocean eddies

Several recent studies have documented the importance of anticyclonic ocean eddies in the intensification of tropical cyclones in the North Atlantic and western North Pacific basins. Studies have also indicated the presence of such eddies in the northeastern Tropical Pacific, mainly during the winter months, but also evident during the tropical cyclone season. In this study, we used the best-track information from the National Hurricane Center to identify tropical cyclones that satisfy the criteria for rapid and explosive deepening in the region during the period 1993-2007. We used sea surface height anomaly data from satellite-based radar altimetry (Ssalto/Duacs-AVISO project) to investigate the interaction of those tropical cyclones with anticyclonic ocean eddies. The relative importance of the ocean eddies and the atmospheric forcing was evaluated using the North American Regional Reanalysis data to calculate: low level vorticity, vertical shear of the zonal wind and tropospheric moisture. The Simple Ocean Data Assimilation dataset was used to calculate sea surface temperature, oceanic heat content and the depth of the 26°C isotherm. The hurricane model developed by Emanuel was used to reproduce some of the cases and investigate its sensitivity to environmental parameters. During the period of interest, we found forty-two cases of rapid deepening and two cases of explosive deepening. From those cases, we determined that 68% of them presented interaction with anticyclonic ocean eddies during their trajectories and 93% of those that interacted with ocean eddies, reached major hurricane classification. These results led us to conclude that tropical cyclone interaction with anticyclonic ocean eddies in the region was the main factor leading to rapid deepening, when favorable atmospheric conditions were present. The largest atmospheric contributors were mid-tropospheric moisture (above 75%) and the absence of high values of zonal wind shear (less than 7 m/s between 850 and 200 hPa). In the ocean the main contributors to cyclone intensity were ocean heat content and the depth of the 26°C isotherm, both of these are locally increased by the presence of anticyclonic ocean eddies in the region.