In Hart (2001: poster presentation in this conference) a phase space for analyzing the lifecycle of cyclones (both warm and cold core) was proposed and examined. In this presentation, one major lifecycle within this phase space is examined: the extratropical transition of tropical cyclones.

The extratropical transition lifecycle is defined within the phase space as beginning objectively when the thermal (thickness) gradient, B, across the cyclone reaches a critical value of 10m within 500km radius. This effectively denotes the beginning of frontogenesis across the previously symmetric cyclone. As frontogenesis and enhanced isentropic lift deform the storm, evolution toward a cold-core structure occurs.

Extratropical transition is completed once the cyclone obtains a cold-core structure, measured objectively through a thermal wind calculation between 900 and 600hPa (see Hart poster in this conference). Comparison of this measure of ET completion to the NHC ET declaration will be shown.

Comparison of these two timings (start and end of transition) gives the transition period length. An analysis of this length, in comparison to TC formation location, cyclone track, cyclone intensity, post-transition intensity change yield great insight into the preferred climatology for cases of explosive ET vs cases of weak ET.