Sensitivity of the Strongest Hurricanes to Ocean Warmth

The past three decades have seen a significant upward trend in the intensity of the strongest hurricanes worldwide that is most pronounced over the North Atlantic. Questions remain about this trend especially its relevance to coastal communities in the United States and elsewhere. This talk focuses on observed changes in the intensity of the strongest hurricanes over the North Atlantic basin and on the spatial pattern of these changes. Results show that the upward trend is significantly related to rising sea-surface temperature (SST) after accounting for El Nino. The trend peaks at 16 m/s per deg C at the 75th percentile with a 90% confidence interval of between 7 and 20 m/s per deg C. The consequences of increasing intensity of the strongest hurricanes is not confined to the open ocean as nearly 70% of all hurricanes that occur over the basin reach a lifetime maximum intensity west of 60W longitude. The largest intensity increases are occurring over the Gulf of Mexico and the Caribbean Sea, where ocean temperatures are warmest and hurricanes are strongest. Decreases in intensity are noted along most of the United States coastline consistent with a hypothesis that continental aerosols act to decrease hurricane intensity. This might help explain why, despite the increasing intensity of basin-wide hurricanes, there is no detectable upward tend in damage costs in the United States.