Impact of Central American Gap-Winds on Intrabasin Variability of Eastern North Pacific Tropical Cyclones During ENSO

Previous studies have shown that El Niño–Southern Oscillation (ENSO) can modulate tropical cyclone (TC) activity over the eastern North Pacific (ENP). Consistent with previous studies, we find that both observed TC counts and accumulated cyclone energy (ACE) are increased (decreased) during El Niño (La Niña) hurricane seasons over the ENP in the basin-wide average. However, there is significant ENSO-driven TC variability within the ENP basin, with a robust suppression in both TC genesis and track density along the Pacific coast of Mexico and Central America during El Niño hurricane seasons. Anomalous low-level relative vorticity associated with ENSO-induced Central America gap-wind (CAGW) variability plays an important role in the intrabasin variability of TC activity, as revealed by a genesis potential index (GPI) analysis using NOAA/NCEP Climate Forecast System Reanalysis (CFSR) data. During El Niño the CAGW intensifies, enhancing the anticyclonic vorticity in the coastal region and contributing to an unfavorable environment for TC genesis. This combined with reduced mid-level moisture transport from the Atlantic basin during El Niño suppresses TC genesis in the coastal region, causing localized reductions in TC activity. These findings suggest that despite increased basin-averaged TC activity in the ENP during El Niño, the intensified CAGW events could decrease the TCs' potential to threaten the west coast of Central America on average.