Introduction
   
    Hurricanes are one of the deadliest natural disasters on our planet, responsible for more deaths than any other single phenomena (Abbott, 2002). Although the number of hurricane deaths in the United States has been dropping, the costs associated with hurricane damage have been increasing as more and more people move to hurricane prone coastlines (Nicholls, 2001; Abbott, 2002).
    Hurricanes follow a generalized life cycle based on wind speed, beginning as a tropical disturbance then progressing to a tropical depression (winds 37-62 km/h). This is followed by designation as a tropical storm (winds 64-117 km/h) and finally a hurricane (winds > 118 km/h) (Slattery and Burt, 1997). The Saffir Simpson hurricane scale further divides hurricanes into 5 categories, also based on wind speed, and to some extent, pressure. Typical hurricane structure includes a calm eye 20-50 km in diameter characterized by low surface pressure (typically ~965 mb), surrounded by the eye wall, and spiral wind and rain bands (Slattery and Burt, 1997).
    Several conditions are required for a hurricane to form in the Atlantic Ocean. Sea surface temperatures need to be greater than 27°C, surface and upper level winds should be light. Easterly waves in the upper troposphere promote hurricane formation in the eastern Atlantic, while upper level westerlies restrict hurricane development. These conditions generally occur between June-November, making these the peak months for Atlantic hurricane activity, though this is subject to interannual variability (Slattery and Burt, 1997).
    Regional and global scale phenomena can have a strong influence on hurricane number and intensity. La Nina events are related to increased hurricane damage in the USA, while El Nino events may help suppress hurricane formation, though exceptions certainly occur (Nicholls, 2001). The transition to La Nina during 1995 resulted in the second worst Atlantic hurricane season since late 1800’s, with 11 hurricanes, 8 tropical storms, 121 deaths, and $7.7 billion US in damages. Slattery and Burt (1997) gave 4 reasons for this situation: 1) the end of El Nino (and its suppression of tropospheric westerlies) resulted in easterly winds at all levels, 2) high rainfall in West Africa suppressed high level winds that otherwise shear off the tops of developing hurricanes, 3) low pressure and high temperature in West Africa caused southerly winds that intensify hurricanes, and 4) stratospheric winds were in the westerly phase of the ~26 month Quasi-Biennial Oscillation (QBO), which can cause twice as many hurricanes as stratospheric easterlies.
     In this project, I ask the how the probability distribution of hurricane intensity and track paths in Caribbean and the South-eastern seaboard of North America changes in response to El Nino and La Nina events in the Pacific Ocean, and how this changes the patterns of risk to life and property in the eastern United States.