Extratropical transition and transformation of southwest Pacific tropical cyclones

Thirty-three cases of extratropical transition (ET) of tropical cyclones in the southwest Pacific during 1970 are investigated using NCEP reanalyses. The sequence of synoptic-scale events accompanying ET and the subsequent transformation to a baroclinic extratropical cyclone is outlined. Composites are used to identify key dynamical forcings on the synoptic scale. One feature common to almost all cases is the appearance of a jet streak in the southeastern quadrant. About ten of the cases underwent regeneration in the extratropics. The propagation of a second upper-level jet into the northwestern sector was a key ingredient in the majority of these redeveloping storms.