Extended Abstract (432K)12D.1
Operational forecasting of extra-tropical transition
Chris Fogarty, Newfoundland Weather Center, Gander, NF, Canada
The Atlantic hurricane season (June through November) is not only a busy time of year for forecasters at the National Hurricane Center in Miami, but also a time when meteorologists north of the border at the Canadian Hurricane Centre and regional weather offices in Eastern Canada are faced with the remnants of many decaying or re-intensifying tropical cyclones. It is not unusual for 4 or more storms to move through Canadian waters in any given year, and recent years have been no exception with landfalling storms such as Hurricane Hortense (September 1996), Hurricane Michael (October 2000) and Tropical Storm Karen (October 2001). More recent near-landfalls include hurricanes Erin and Gabrielle (September, 2001).
From a forecasting perspective, areas of Eastern Canada are often prone to heavy rains from storms undergoing transition owing to the characteristic left-of-track redistribution of convective activity. Post Tropical Storm Gabrielle dumped as much as 6 inches (150 mm) of rain to southeastern Newfoundland as a result of this "lop-sided" convection. It is also well understood (and not surprisingly) that the highest winds from these accelerating storms are typically to the right of the storm track and the radii of gale- and storm-force winds right of the track are often twice that than to the left. It is also observed that storms undergoing transition while embedded in the mid-latitude flow initially move at roughly 75% or more of the speed of the 500 mb geostrophic flow.
Various rules-of-thumb, such as those above, will be discussed in this presentation plus other quick-and-easy operational techniques used in effectively issuing forecasts and warnings. A typical forecasting procedure will be outlined in this talk with references made to 500-mb height and vorticity fields. The thought process begins with basic pattern recognition and some examples will be shown to demonstrate different scenarios of extra-tropical transition.
Supplementary URL: http://www.geocities.com/novaweather/ET_schematic.html
Session 12D, tropical cyclone extratropical transition (Parallel with Sessions 12A, 12B, and 12C)
Thursday, 2 May 2002, 8:30 AM-10:30 AM
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