The Variability in Atlantic Ocean Basin Hurricane Occurrence and Intensity as Related to Enso and the North Pacific Oscillation

The investigation of the effect of El Nino-related variability on hurricane activity has been a popular topic of study. Studies have shown that there are fewer Atlantic Ocean basin hurricanes during an El Nino year than during a La Nina year. Various atmospheric and oceanic parameters that influence hurricane development become significantly altered during an El Nino event, leading to suppressed easterly wave development and growth. The effect of the El Nino / La Nina cycle on hurricane intensity, however, is not straightforward. Studies addressing the interannual variability of hurricane intensity have captured far less attention than the more generalized subject of hurricane occurrence. This study examined the interannual variability of hurricane intensity (measured as wind speed and interpreted through the SaffirSimpson Scale) from 1938 through 1999. These data were then compared with the occurrence of El Nino / La Nina events as defined using the Japan Meteorological Agency (JMA) index. El Nino / La Nina variability superimposed on variability associated with the North Pacific Oscillation (NPO) was also examined here. Not surprisingly, during an El Nino year the intensity of Atlantic hurricanes was found to be weaker than during a neutral year or a La Nina year. There were also significant differences found in hurricane intensity between El Nino and La Nina years when the NPO was in phase 1, rather than when the NPO was in phase 2. Finally, this study also examined the interannual variation in hurricane intensity by genesis region (i.e., the eastern and western Atlantic Ocean Basins, the Caribbean, and the Gulf of Mexico).