Vorticity Profiles of Tropical Cyclones in the Atlantic Basin

Tropical cyclones (TCs) have taken the spotlight in the United States over the past two hurricane seasons, with storms such as Hurricanes Harvey, Irma, Maria, Florence, and Michael leaving lasting impacts on different regions of the country. While track forecasts have been improving greatly over the past decade, TC intensity and genesis forecasting are still lacking the edge required to protect the infrastructure supported by the southern and eastern United States. Many studies have been conducted investigating intensity cycles of TCs using proxies such as lighting and infrared patterns and signatures. This study uses Global Forecast System (GFS) model forecasts of the absolute vorticity at 10 selected vertical pressure levels to discover patterns in the magnitude, shape, and vertical depth of the vorticity maxima associated with several TCs as well as in the vertical gradients of the vorticity values over the lifetime of the storms. The signs of the vertical gradients of absolute vorticity confirm the dynamics and structure of a healthy tropical cyclone. Patterns and trends in the vertical vorticity gradients illustrate the effects of storm-land interaction on the structural stability of the TC. Changes in the magnitude of the vorticity maximum can indicate strengthening or weakening of the storm. Tropical cyclogenesis can be forecast by finding the time at which lower level vorticity sources link vertically with a mid-level vorticity source, such as an African Easterly Wave. Finally, the vertical depth of the vorticity maximum is related to the inertial stability of the TC, helping to forecast how long the storm will be able to retain its tropical characteristics. These elements could potentially be applied to the operational forecasting of TCs and could help quantify anticipated impacts on a given area forecast to be affected by a future landfalling TC.