The lifecycle of extratropically transitioning north Atlantic tropical cyclones was defined objectively by Evans and Hart (2003) in the 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, 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.