November Sunsets and the end of Hurricane Season

Pictured here, some recent sunsets. Click on any image to enlarge.

It doesn't feel much like fall in Florida. The temperatures remain in the mid 80°s F. (29° C.) and the bugs are as thick and vicious as I've ever seen.

Hurricane season officially runs until the end of November, but historically there are few storms in November, despite the continued heat.



Hurricane Rina, the last named storm is long gone, and the tropical Atlantic is quiet, with no threat areas to discuss, and no models predicting development of a tropical depression during the coming seven days. So, is Hurricane Season 2011 finished or will this seventh-busiest hurricane season of all-time spawn a Tropical Storm Sean?

Since the active hurricane period we are in began in 1995, ten of the sixteen years (62%) have seen one or more Atlantic named storms form after November 1, for a total of fifteen late-season storms.



There have been only seven major Category 3 or stronger hurricanes in the Atlantic after November 1. The storms that do form tend to do so from extratropical low pressure systems that get cut off from the jet stream and linger over the warm waters of the subtropical Atlantic. These type of systems typically get their start in the middle Atlantic, far from land, and end up recurving northeastwards out to sea.



The oceans are certainly warm enough to support continued development of tropical cyclones. Sea Surface Temperatures over a wide area of the tropical Atlantic are 0.5 - 1.0°C above average, and are well above the 26°C (79°F) threshold typically needed to support tropical storm formation. However, wind shear is starting to rise over much of the tropical Atlantic as the jet stream moves farther south in its normal seasonal cycle.

Wind shear over most of the Atlantic will be too high to support tropical storm formation over the coming two weeks, according to the latest run of the GFS model. Only the southern Caribbean and a few transient pockets in the middle Atlantic east and southeast of Bermuda will have low enough wind shear to support tropical storm formation over the next two weeks.



The African Monsoon is quiet this time of year, and we no longer have African waves coming off the coast of Africa that can act as the seeds for formation of a tropical storm in the Caribbean. If we do get a tropical storm, it will probably be to the northeast of the Lesser Antilles, far from land, in a region where an extratropical low pressure system gets cut off from the jet stream and lingers long enough over warm waters to acquire tropical characteristics and get a name.

Both the GFS and ECMWF models are suggesting a system like this may take form 7 - 10 days from now. Taking all these factors into account there is still some chance, perhaps better than 50%, that another named storm will form, however it will likely form far out in the Atlantic and stay out to sea, not affecting land.