Thursday, 2 August 2001: 4:15 PM
The rapid growth and decay of a low-latitude extratropical cyclone in the central Pacific Ocean
The rapid development and subsequent rapid decay of a surface cyclone in the central Pacific Ocean on 5-6 November 1986 is examined. The storm of interest was distinctly extratropical in origin despite developing at an unusually low latitude (~30N). The rapid surface cyclogenesis was preceded by the similarly rapid development of a vigorous upper-level jet/front system by 0000 UTC 5 November. In the subsequent 12-h period, the surface cyclone deepened by 24 hPa while remaining nearly stationary. Concurrent with the remarkable surface development was a cyclonic wrapping of the associated tropopause-level potential vorticity (PV) anomaly which allowed that feature to briefly acquire a negative tilt. Large-scale deformation arrested this tendency after 1200 UTC 5 November and the tropopause PV anomaly receded to lower pressures, acquired a positive tilt, and was stretched in the NE-SW direction over the next 24 h. A 12 h period of little or no surface development was then followed by a period of rapid cyclolysis in which the sea-level pressure minimum filled by 12 hPa in the 12 h ending at 1200 UTC 6 November.
The dramatic fluctuations in the intensity of this cyclone are diagnosed using piecewise PV inversion of the output from a successful simulation of the event performed using the Penn State/NCAR MM5. The respective roles of the upper-level, lower boundary and diabatically generated PV anomalies in producing the unusually rapid growth and decay of this cyclone are presented. A comparison of the rapid cyclolysis in this case to that observed previously in high latitude Pacific cyclones is offered.