Analysis and prediction of Atlantic tropical cyclone activity

Abstract

This work begins with the development of a statistical prediction model of numbers of tropical storms, hurricanes and major hurricanes per year in several regions of the Atlantic: the entire Atlantic, the Caribbean Sea and the Gulf of Mexico, as well as landfalling storms along the US Gulf of Mexico, Southeast and Northeast coasts. The methodology involves of cross-correlating variables against Empirical Orthogonal Functions (EOFs) of the Hurricane Track Density Function (HTDF) to select predictors. The model performs well in the basin-wide predictions over the entire Atlantic and Caribbean, with the predictions showing an improvement over climatology and random chance at a 95% confidence level. Over the Gulf of Mexico, only named storms showed that level of predictability. Predicting landfalls proves more difficult, and only the prediction of named storms along the US Southeastern and Gulf Coasts shows an improvement over random chance at the 95% confidence level. Tropical cyclone activity along the U.S. Northeastern Coast is found to be unpredictable in this model; with the rarity of events, the model is unstable. In order to provide some physical basis for many of the connections found statistically, the second section is a case study of the 2004-07 Atlantic hurricane seasons. It is found that 2005 had the most favorable SST and vertical wind shear conditions over the main development region. 2004 and 2006 had intermediate levels of SST and wind shear and, outside of the month of August, similar levels of activity. Activity in 2007 was generally suppressed: although more tropical storms formed than in 2006, they were very short-lived. On average, tropical storms in 2007 survived less than 2.5 days. The strength of the subtropical anticyclone is a very important factor: in 2005, a weak subtropical high allowed for unusually high SST in the main development region, while in 2007 a strong subtropical high over the east Atlantic cooled SST and increased vertical wind shear. The strength of the subtropical cyclone may be related to the heat release of the African monsoon. This finding also emphasizes the importance of factors relating to the strength of the subtropical high pressure in hurricane prediction.