AL012015 (Ana) Off the GA/SC Coast

The US National Hurricane Center has started tracking the system off the SEUS as “Subtropical Storm Ana”.  Here is the current forecast wind swath using my Taru(tm) model and the NHC forecast track:
ana_fri_am_track

Winds could reach tropical storm strength right along the coast where this think moves onshore, with widespread areas (seen in blue) of gust winds.  Impacts are forecasts to be light; it’s likely any efforts to prepare extensively (especially evacuations, shutdowns, etc.) would cost more than the storm itself, but it’s a good idea to review your hurricane plans, get dead limbs out of the way and clean up possible debris, prepare for some scattered power outages, those kinds of things.  Consider it a test run for the real thing.

So just what is a “subtropical storm”?  First some quick abbreviated definitions.  A tropical cyclone (the family that is commonly called hurricanes or tropical storms) is defined as warm core low pressure system with winds above a given threshold (34 knots).  Tropical low pressure systems have a relative, the extratropical cyclone or mid-latitude cyclone.  Extratropical cyclones are fairly common, but can form nor’easters, which are intense, cold-core low pressure systems, sort of the cold cousin of the hurricane.  Subtropical cyclones are hybrids.  The have a cold or cool core but are taking on some tropical characteristics such as the development of thunderstorms near the center of circulation. There is a spectrum of low pressure systems with various characteristics like wind fields, temperatures, and driving mechanisms. Like many things in nature, weather systems sometimes don’t fit into nice neat categories.

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