The TT problem: Forecasting the tropical transition of cyclones

The Tropical Cyclone Reports states that the development of nearly half of the Atlantic tropical cyclones from 2000 to 2003 depended on an extratropical precursors. A fundamental dynamic and thermodynamic transformation of such disturbance is required to create a warm-core tropical cyclone. The process is referred to as tropical transition (TT), to be contrasted with extratropical transition (ET), which results in an extratropical disturbance given a tropical cyclone. Focusing on the Atlantic basin, this paper reviews briefly what is known about TT and how it can be anticipated. While TT storms typically do not exceed Category 2 intensity, their tendency to form close to North America can create significant forecast and evacuation problems.