Effect of winter-to-summer El Niño transitions on tropical cyclone activity in the North Atlantic

Abstract

El Nino-Southern Oscillation (ENSO) is known to significantly modulate Atlantic tropical cyclone (TC) activity. In this paper, we separate El Nino events into El Nino resurgence (ELR) and La Nina-transition-El Nino (LAT) events according to the warm or cold ENSO phase in the preceding winter. Different influences of the two types of El Nino events on North Atlantic TC activity are explored during the hurricane season of June–November. The average number of TCs is more, with shorter average duration and slightly larger intensity during ELR events than during LAT events. There are more TCs passing through and making landfall at the Gulf of Mexico, Caribbean Sea during ELR events, indicating that TCs may have a greater impact on coastal cities of Gulf of Mexico and Caribbean Sea during ELR events than LAT events. Composite analysis reveals that thermodynamic factors such as relative humidity (RH), sea surface temperature and tropical cyclone heat potential are mainly responsible for the TC activity difference between ELR and LAT events. Genesis potential index diagnosis shows that the RH and potential intensity are the dominant factors that influence TC genesis in the MDR during ELR events. During LAT events, the relative vorticity, vertical wind shear and RH over Cape Verde are favorable for TC genesis. In summary, the preceding winter ENSO phases associated with ELR and LAT events lead to opposite changes of environmental factors, and thus induce different TC activities in ELR and LAT events.