Impacts of the Three-Dimensional Oceanic Thermal Structure and Translation Speed during North Atlantic Hurricanes Emily and Wilma in 2005

Long standing research has shown that high sea surface temperatures (SSTs) are an important prerequisite in the formation and maintenance of tropical cyclones. However, this research seeks to investigate the role of the three-dimensional oceanic thermal structure and translation speed (U_h) on the cyclogenesis and intensity fluctuations during category 5 (i.e., winds > 70 m s^-1) Hurricanes Emily and Wilma in 2005. In order to determine the state of the three-dimensional oceanic thermal structure during these storms, the depth of the 26°C isotherm was utilized (D26). In addition, hourly-interpolated along-track measurements of wind speed (U₁₀) and translation speed (U_h) were incorporated to increase data sampling.

Results indicate that both storms encountered oceanic mesoscale features (i.e., warm-core eddies and cold-core eddies). It was found that D26 increased within warm-core eddies (WCEs) as warm waters extended deep down into the water column (> 100 m), thus enhancing intensity. Hurricane Emily’s U₁₀ increased to 70.5 m s^-1 shortly after traveling directly over a large WCE where a maximum D26 value of 136.4 m was present on 16 July. In contrast, near cold-core eddies (CCEs), strong upwelling caused low D26 values (< 70 m), thus weakening the storms. Hurricane Wilma’s U₁₀ was found to decrease from over 80 m s^-1 to 69.4 m s^-1 while encountering a CCE on 19 – 20 October. Although U_h was found to be an important factor as it determined the time spent over these oceanic features. Two multiple regression models run on each storm with D26 and U_h as the independent variables and U₁₀ as the dependent variable showed moderately strong explanatory power for each hurricane. The model results for Hurricane Emily indicate that D26 and U_h had a moderate influence on U₁₀ along-track, as seen with an adjusted r-squared value of 0.5560. Hurricane Emily’s model reveals that the two variables D26 and U_h had some role in the intensity fluctuations with an adjusted r-squared value of 0.4139.