26th Conference on Hurricanes and Tropical Meteorology


The extratropical transitions of eastern Pacific Hurricane Lester (1992) and Atlantic Hurricane Andrew (1992): A comparison.

Michael Dickinson, Univ. at Albany/SUNY, Albany, NY; and L. F. Bosart, K. L. Corbosiero, S. Hopsch, K. Lombardo, M. J. Novak, B. Smith, and A. C. Wasula

Considerable attention has been given to the transition of tropical cyclones to extratropical cyclones in the recent literature. This process is referred to as extratropical transition (ET). A review of the literature reveals that ET occurs in the Atlantic, western Pacific, and Australian tropical cyclone basins. The only region to experience frequent tropical cyclones and not experience ET is the eastern Pacific. It has been argued that the synoptic- scale environment is not conducive to the ET process in this region. This work will show a bonafide example of an eastern Pacific ET event. The transitions of Hurricanes Lester and Andrew (1992) are examined using the 1.125 degree European Centre for Medium Range Weather Forecasting operational analyses. Hurricane Lester (1992) made landfall on the Baja Peninsula and northwestern Mexico near 0000 UTC 24 August ahead of a broad, synoptic-scale, positively tilted trough. The Lester circulation continued to move north-northeastward ahead of the approaching trough. Transition occurred as Lester became embedded within the 200-1000 hPa thickness gradient, indicating that Lester no longer maintained a warm core structure. While the remnants of Lester did not reintensify, the ET process resulted in considerable precipitation (in excess of 60 mm) from Arizona/New Mexico, northeastward through Colorado and Nebraska.

The trough continued eastward where it then interacted with Hurricane Andrew over the southeastern US by 0000 UTC 28 August. This interaction led to a more "classic" transition event where the trough became cyclonically wrapped (LC1) and the low-level vorticity remnants of Andrew reintensified.

One of the interesting aspects of this study is that one trough was responsible for the transition of two storms. The upscale effects of the ET process was considerably different in each case. The difference in low- level and upscale responses to each transition suggests that there are many flavors of ET.

extended abstract  Extended Abstract (3.7M)

Session 17D, tropical cyclone extratropical transition II
Friday, 7 May 2004, 10:15 AM-11:30 AM, Napoleon III Room

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