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Hurricane Season may be Over, but Storms Can Still Form

2 Dec 2017, 8:49 pm

The 2017 Atlantic hurricane season is officially finished. The season ended on Thursday, November 30. However history tells us that tropical cyclones can still form during the “off-season” which we are in now.

“Zeta” which was part of the incredibly-busy 2005 hurricane season, spanned two years from December 30, 2005 to January 7, 2006. Picture courtesy NASA

The Atlantic hurricane season spans from June 1 to November 30. This is when most tropical cyclone activity takes place. It is estimated that 97% of all tropical cyclones occur between those dates. This is a period in the calendar year (here in the Northern Hemisphere) when the sea surface temperatures are warmest and disruptive winds, known as wind shear, can weaken significantly. These factors help generate tropical cyclones.

The activity chart for tropical cyclones across the Atlantic during the calendar year between May and December. The peak of the season is during the second week of September.

When storms form in the hurricane off-season they usually stay at a tropical storm status or weaker. That means the sustained winds remain below 73 miles per hour. This is because there is far less energy and opportunity for storms to strengthen during the winter.

The number of storms that have formed in the hurricane off-season (that we know of and have records of) show most don’t get to hurricane status.
The monthly activity for the Atlantic Basin during the off-season shows most storms form in May, followed by December, with a sharp drop off in the peak winter months.

While on the rare side, off-season tropical cyclones can occur across the Atlantic Ocean, Gulf of Mexico, and Caribbean. These storms usually do not reach hurricane status with dangerous storm surge and winds, but rather produce the biggest hazard of heavy rainfall. If any storms do form outside of the season, we will surely let you know and give you the forecast for that specific storm.

For WeatherNation, Meteorologist Steve Glazier

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