Extratropical Transition of Southwest Pacific Tropical Cyclones. Part II: Midlatitude Circulation Characteristics

Abstract

Abstract This second of two papers on extratropical transition (ET) over the southwest Pacific Ocean focuses on the variability of ET. A climatology of ET onset based on a previously described objective technique shows that ET commences 15° of latitude nearer the equator on average than similar cases from the Northern Hemisphere. Characteristic midlatitude circulation patterns accompanying ET near 30°S are identified by means of empirical orthogonal function (EOF) analysis of 50 storms. The first eigenvector pattern, explaining nearly half the circulation variability, expresses relaxed and enhanced pressure gradients south of the storm that define composites similar to “cradled” and “captured” classifications previously described for the southeast Indian Ocean. The second EOF distinguishes redeveloping from weakening storms. Reintensifying storms were located beneath strong cyclonic vorticity advection (CVA) near the equatorward entrance region of an upper jet whereas the upper jet was well to the west of...