Nov 20, 2019

Tropical Storm Sebastien Forms in Atlantic

Atlantic Ocean
by
Bob Henson
,
Weather Underground

The Atlantic tapped us on the shoulder Tuesday morning with the formation of Tropical Storm Sebastien, reminding us that hurricane season isn’t over for a couple more weeks. The disturbance formerly known as 90L was designated Sebastien at 11 am EST Tuesday, with top sustained winds of 45 mph. Sebastien was located almost 300 miles northeast of the Leeward Islands, moving north-northwest at 8 mph over open waters.

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After drifting slowly north-northwest for the next day or two, Sebastien will get swept up into a strong midlatitude front and upper-level trough moving off the U.S. East Coast, pushing the storm toward the northeast. It’s quite possible Sebastien will take on subtropical characteristics as it interacts with the front and trough and as wind shear increases further. Sebastien’s winds may actually increase as it moves toward its ultimate fate as an extratropical frontal low. With no land masses in its immediate path, Sebastien will pose no problems for any populated areas while it remains a named storm.

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Dr. Jeff Masters, who now pens the Eye of the Storm blog for Scientific American, provides us with some climatological perspective on our latest Atlantic storm.

“Sebastien’s formation gives the Atlantic 18 named storms for the season—pretty rare territory, since only 8 other seasons since 1851 have had 18 or more named storms. Since storms began getting names in 1950, the only Atlantic named storms beginning with “S” have been Sebastien (1995), Stan (2005), Shary (2010), Sean (2011), and Sandy (2012). Both Stan and Sandy had their names retired.

“Sebastien’s formation brings the Atlantic tally for 2019 to 18 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE index of 124.1. The 1981 – 2010 averages for these quantities by November 19 were 11.6 named storms, 6.2 hurricanes, 2.7 intense hurricanes, and an ACE index of 102.3, according to Dr. Phil Klotzbach, so 2019 is near or above average in all metrics.”