A Tropical System Meets the Changing Season

By: Bryan Norcross , 8:50 PM GMT on October 21, 2012

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The most accurate computer forecast models are in amazing agreement today, and if they are right, a system will move out of the Caribbean this week having significant effects on the northern Caribbean islands, the Bahamas, and perhaps the East Coast of the U.S. The scenario is complicated involving both tropical and wintertime atmospheric features - but it's not impossible.

In some ways this is reminiscent of Hurricane Noel in 2007 which caused devastating flooding in Cuba, Haiti, the Dominican Republic, and the Bahamas. In addition, several days of strong onshore wind caused millions of dollars of beach erosion along Florida's east coast, with strong winds in New England and Atlantic Canada as well. The peak winds during the multi-day onslaught were sustained at 43 mph with gusts to 54 mph in Miami Beach. On Nantucket the winds gusted to 72 mph and in Newfoundland they recorded gusts of 112 mph.

An organized low pressure system hasn't even formed yet in the Caribbean, so a LOT can happen, but because the scenario is so dramatic, it's going to require our attention.

In a nutshell, the models show a strengthening tropical system bringing flooding rains to the Caribbean islands and the Bahamas. Then the northern jet stream grabs it, injects some energy, and the storm moves north along the U.S. east coast and evolves into a VERY strong Nor'easter... all the way up to Atlantic Canada. Nor'easters wrapped with tropical moisture can be nasty because you get the contrast of extremely moist southern air and cold northern air in the same circulation.

Along the east coast of Florida, if anything like this scenario plays out, the combination of the tropical low pressure in the Caribbean and the high pressure to the north will bring increasing onshore winds all week, becoming very windy by late in the week. The worst of the rain would stay offshore, but significant erosion and flooding at high tide would seem likely.

Farther north, the forecast models show a monster nor'easter affecting the entire East Coast of the U.S. through next weekend, with coastal rain and wind and likely snow inland, but a small difference in track would make so much difference in the effects a week from now, it's just something to watch at this point.

You might say, "this all seems pretty implausible", and I can't remember one exactly like this. But, recall that last winter we were stuck in a pattern that resulted in spectacularly warm weather in the north because of a "blocking" high pressure system in the North Atlantic. Well, the models are developing a big blocking high again next weekend, and that forces the system on a more northerly track than normal... along the coast. Most storms in October head northeast out to sea.

The bottom line, unusual/extreme weather patterns often yield unusual/extreme weather. This is pretty unusual, so it bears watching closely. Stay tuned.

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3. WunderAlertBot (Admin)
12:14 PM GMT on October 22, 2012
bnorcross has created a new entry.
2. TropicalAnalystwx13
8:59 PM GMT on October 21, 2012
Thanks Mr. Norcross. It's definitely something to watch for sure.
Member Since: July 6, 2010 Posts: 113 Comments: 31502
1. Grothar
8:54 PM GMT on October 21, 2012
Thanks, I was wondering when you were going to come out with a blog. You know how we Floridians get. Good blog. Should be interesting to see what develops.
Member Since: July 17, 2009 Posts: 69 Comments: 25378

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About bnorcross

This is the official blog for Bryan Norcross, Hurricane Specialist at The Weather Channel.

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