Observations of Wind Asymmetries in Atlantic Tropical Cyclones

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Sunday, 4 January 2015
Erin Mary Dougherty, University of Virginia & SOARS, Charlottesville, VA; and C. A. Davis and R. E. Davis

Most major cities are located on coastlines, vulnerable to the direct impacts of tropical cyclones. Therefore, it is critical to understand and improve prediction of these storms in order to make communities more resilient. Though hurricane warning systems have improved in recent years, these warnings are insufficient, because they fail to account for an indication of tropical cyclone wind asymmetry, or the radial extent of maximum winds in different locations within the cyclone. This study explored the wind asymmetry (defined by magnitude and orientation) among 337 Atlantic tropical cyclones from 1988-2012, utilizing the National Hurricane Center's (NHC) Extended Best Track Dataset (EBT) and Statistical Hurricane Intensity Prediction Scheme (SHIPS). Asymmetry was defined as the magnitude of the largest difference in the radius of gale-force wind across opposing quadrants, normalized by the average of the four wind radii. The asymmetry orientation pointed along the axis of maximum asymmetry toward the quadrant with the greater gale radius. Relationships between wind asymmetry and various storm characteristics such as geographical location, storm life cycle, intensity, size, storm motion, and vertical wind shear were examined. The magnitude of asymmetry increased in higher latitudes and along coastlines, particularly in smaller storms. Asymmetry was higher at the beginning of a storm's life, possibly owing to a less well-organized structure, and higher near the end of a storm's life, coinciding with an increase in vertical wind shear and translation speed. Results from this study may allow for improved tropical cyclone forecasts and warnings to help protect seaside communities.