Examining Intensity Trends During Extratropical Transition

Extratropical transition (ET) is the transition which a tropical cyclone (TC) makes once it starts interacting with upper-level troughs, called shortwaves. During this process, forecasting storm intensity and storm track becomes a challenge. A prime example of this is problem is Hurricane Sandy (2012), which interacted with a cold front, enhancing the effects of the storm upon landfall. This study will examine the environmental factors present during ET to help improve statistical-dynamical forecasting techniques such as Statistical Hurricane Intensity Prediction Scheme (SHIPS). ET cases in the North Atlantic basin from 1982 to 2014 are examined. The storms with winds greater than 64 kt are categorized as ones that weaken and intensify over a 24-h period during ET. To identify potential differences in weakening and intensifying systems, the following storm and environmental variables are evaluated: storm track, storm motion, sea surface temperatures, temperature at 150 hPa, theta-e difference between the air parcel and the environment, temperature gradient between 850 and 700 hPa, tangential winds at 500 hPa, tangential winds at 300 hPa, magnitude of deep layer shear, and azimuthally averaged meridional velocity from 0 to 500 km. Storm track and motion between weakening and intensifying storms lacked a discernible pattern. A similar story arises from environmental variables temperature gradient and shear, two variables often used as indicators for ET. However, the theta-e difference and tangential winds at 500 hPa appear to indicate a 'healthier' warm core at the beginning of ET allows for intensification during baroclinic interaction.