The lifecycle of extratropically transitioning (ET) north Atlantic tropical cyclones was defined objectively by Evans and Hart (2003) in a cyclone phase space(Hart 2003). The ET storm trajectory progresses from symmetric warm-core to asymmetric cold-core structure. The point at which a significant thermal gradient across the cyclone was first observed (B=10m) was defined as the beginning of transition (TB) with the end of transition (TE) defined when the 900-600hPa thermal wind becomes cold-core.

Fifteen north Atlantic tropical cyclones (1998-2002; AVN operational analyses) that underwent extratropical transition have been composited in storm-relative coordinates to determine the common aspects of the synoptic environment associated with ET. In this talk, four specific points in the ET lifecycle will be examined: 1) TB-48hr, 2) TB, 3) TE, and 4) TE+24hr. Both the composited mean conditions, and the individual storm departures from that 15-cyclone mean are considered. The factors influencing whether a tropical cyclone intensifies after transition completes or dissipates are reviewed. Further preliminary indications of the impacts of a synthetic (bogus) vortex on post-transition storm structure evolution within the operational analyses are gained by examining differences in the mean conditions at TE+24hr between the AVN and NOGAPS analyses.