Final Month Of Season Off To A Quiet Start

Last week was quite a week in weather around North America.  Weather forecasters were dealing with a hurricane and a historic nor’easter that brought snow to many parts of the Eastern Seaboard of the United States.  Hurricane Rina was a major hurricane that ultimately fizzled thanks to the influence of dry air pushing into the Gulf of Mexico, and strong wind shear from the south.

What happened with Rina is typical of Atlantic Hurricanes this time of year.  As we transition from summer to winter, the jet stream changes.  With the days getting shorter, there is less daylight so the planet is giving off more energy than it is taking in.  Moreover, the major circulation belts around the planet begin to migrate south in response to the sun’s retreat toward the Tropic of Capricorn, which ends on the first day of winter in the Northern Hemisphere.

Consequently, the jet stream pushes farther south, and brings cooler and drier air along with hostile shearing winds.  The dry air and shear are two things that tropical systems do not like.  Tropical storms and hurricanes like warm moist air, and light upper level winds.  So, when you get into the latter part of October and November, tropical cyclones become rare in the Atlantic.  There are exceptions to the rule though.  Hurricane Kate in 1985, Hurricane Gordon in 1994, Hurricane Lenny in 1999, and Hurricane Michelle in 2001 are notable examples.

The common area of development for tropical systems in the Atlantic in November is usually in the Southwestern Caribbean where sea surface temperatures are still very warm.  With these waters very close to the equator, they get plenty of exposure to the sun, which oscillates between the Tropic of Cancer (23 degrees North latitude) and the Tropic of Capricorn (23 degrees South Latitude).  In addition, the Southwestern Caribbean sees very little in the way of wind shear even this time of year.

On average, there is about one storm every two years during the month of November.  Despite that, there has only been one storm that has emerged in the Gulf of Mexico since 1950, and that developed in the Bay of Campeche region.  Of those 30 or so storms, a hurricane has emerged every two or three years, and a major hurricane has developed once every dozen years.  Right now, there are no threats as the final month of the season is off to a quiet start.

There are several areas of disturbed weather being tracked right now.  One is in the Eastern Caribbean creating showers and storms for Puerto Rico.  A couple are in the Central Atlantic although one of them appears to be a trough.  The last one is in the Eastern Atlantic to the southwest of the Cape Verde Islands.  None of these disturbances are showing any signs of development at the moment.