Changes in the frequency of U.S. landfalling hurricanes with respect to the El Nino-Southern Oscillation (ENSO) cycle are assessed. Ninety-eight years (1900-97) of U.S. landfalling hurricanes are classified, using sea surface temperature anomaly data from the equatorial Pacific Ocean, as occurring during an El Nino (anomalously warm tropical Pacific waters), La Nina (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. Last, the frequency of major U.S. landfalling hurricanes (sus-tained winds of 96 kt or more) with respect to ENSO phase is assessed empirically. The results indicated that El Nino events show a reduction in the probability of a U.S. landfalling hurricane, while La Nina shows an increase in the chance of a U.S. hurricane strike. Quantitatively, the probability of two or more landfalling U.S. hurricanes during an El Nino is 28%, of two or more landfalls during neutral conditions is 48%, and of two or more landfalls during La Nina is 66%. The frequencies of landfalling major hurricanes show similar results. The probability of one or more major hurricane landfall during El Nino is 23% but is 58% during neutral conditions and 63% during La Nina.

Recent predictions of increased hurricane activity in the Atlantic basin, as well as explosive coastal population growth, have prompted a study of the trends in quantity and intensity of U.S. landfalling hurricanes in the Gulf of Mexico. Gulf of Mexico hurricane landfalls from Cape Sable, Florida, to Brownsville, Texas, are binned by decade from 1886 to 1995 to determine whether gulf hurricane landfalls are becoming more or less frequent. From these bins, subsets of intense hurricanes (sustained winds of 96 kt or more) per decade are also made. The results show that there is no sign of an increase of hurricane frequency or intensity in the Gulf of Mexico at this time.