An Investigation of the Tropical Cyclogenesis of Arlene (2005) Using ERA-Interim Reanalysis and the WRF Model Simulation

Abstract

The process and development sequence of meso-beta-scale vortices at multiple levels and the synoptic-scale environmental conditions for the genesis of Tropical Storm Arlene (2005) were analyzed using ERA-Interim Reanalysis data and Weather Research and Forecasting (WRF) model simulations. Results from the two agree in that although the confluence of low-level westerly winds from the eastern North Pacific and low-level easterly winds from the North Atlantic preceded tropical cyclogenesis over the western Caribbean Sea, midlevel enhanced wind surges over Lake Nicaragua were also important in the pregenesis period. A closer examination of the WRF simulation revealed that the midlevel enhanced wind surges were produced by the interactions between the 500 hPa anticyclone over Mexico and a wind stream from northern South America. The 500 hPa surges augmented the vorticity of the incipient storm as it passed over Lake Nicaragua. Due to the subsequent influxes of strong westerly and easterly winds in the lower atmosphere, the midlevel vortex development was followed by a low-level vorticity increase, enhancing the vertical structure of the vortex motion of the storm from the 500 hPa level downward. This vortex development resulted in tropical cyclogenesis at 1800 UTC on 8 June and a tropical storm by 0600 UTC on 9 June.