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99L is currently being described by the NHC in their Tropical Weather Discussion as being non-tropical at this time (4PM 9/5/07). It looks like a pretty good spinner to me. The NHC is also saying that a small increase in organization could result in the formation of a tropical or subtropical cyclone. Hurricanes and tropical storms that move into the northern latitudes and are petering out are typically described as becoming extratropical. Can someone please help me understand the difference between them all? |
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Tropical cyclones are warm-cored entities -- tropical storms, hurricanes, etc. Wind speeds are at a maximum close to the center. Extratropical cyclones are most easily described as "things with fronts." Highly asymmetric, tilt to the west with increasing altitude, can be cold or warm-cored in nature. Wind speeds are at a maximum a fair distance away from the center. Subtropical cyclones lie between the two. They are usually extratropical cyclones that have cut-off from the midlatitude flow and have hybrid characteristics -- a little bit of both types with most characteristics lying between the two extremes. Often warm-cored at the surface but cold-cored aloft. |