EFFECT OF EL-NINO ON US LANDFALLING HURRICANES, REVISITED

Changes in the frequency of U.S. landfalling hurricanes with respect t o the El Nino-Southern Oscillation (ENSO) cycle are assessed. Ninety-e ight years (1900-97) of U.S. landfalling hurricanes are classified, us ing sea surface temperature anomaly data from the equatorial Pacific O cean, as occurring during an El Nino (anomalously warm tropical Pacifi c waters), La Nina (anomalously cold tropical Pacific waters), or neit her (neutral). The mean and variance of U.S. landfalling hurricanes ar e determined for each ENSO phase. Each grouping is then tested for Poi sson distribution using a chi-squared test. Resampling using a ''boots trap'' technique is then used to determine the 5% and 95% confidence l imits of the results. Last, the frequency of major U.S. landfalling hu rricanes (sustained winds of 96 kt or more) with respect to ENSO phase is assessed empirically. The results indicated that El Nino events sh ow a reduction in the probability of a U.S. landfalling hurricane, whi le La Nina shows an increase in the chance of a U.S. hurricane strike. Quantitatively, the probability of two or more landfalling U.S. hurri canes during an El Nino is 28%, of two or more landfalls during neutra l conditions is 48%, and of two or more landfalls during La Nina is 66 %. The frequencies of landfalling major hurricanes show similar result s. The probability of one or more major hurricane landfall during El N ino is 23% but is 58% during neutral conditions and 63% during La Nina .