Changes in the frequency of U.S. landfalling hurricanes with respect to the El Niño - Southern Oscillation (ENSO) cycle are assessed. Ninety-eight years (1900-1997) of U.S. Landfalling hurricanes are classified, using sea surface temperature anomaly data from the equatorial Pacific Ocean, as occurring during an El Niño (anomalously warm tropical Pacific waters), La Niña (anomalously cold tropical Pacific waters), or neither (neutral).
The mean and variance of U.S. landfalling hurricanes are determined for each ENSO phase. Each grouping is then tested for Poisson distribution using a Chi-squared test. Resampling using a ‘bootstrap’ technique is then used to determine the 5 and 95% confidence limits of the results. Lastly, the frequency of major U.S. landfalling hurricanes (sustained winds of 96 kts or more) with respect to ENSO phase is assessed empirically.
The results indicate that El Niño events show a reduction in the probability of a U.S. landfalling hurricane, while La Niña shows an increase in the chance of a U.S. hurricane strike. Quantitatively, the probability of 2 or more landfalling U.S. hurricanes during an El Niño is 28%; 2 or more landfalls during neutral conditions is 48% and 2 or more landfalls during La Niña is 66%. The frequencies of landfalling major hurricanes show similar results. The probability of 1 or more major hurricane landfall during El Niño is 23%, but is 58% during neutral conditions and 63% during a La Niña.