An early start to hurricane season? “Subtropical” storm may be forming…

January 13

Tropical storms have occurred during every month in the Atlantic, but January storms are rare.  Today, Subtropical Storm Arthur could be forming about 2,000 miles east of the Bahamas.


Visible satellite image from 9:15 am this morning. (NASA)

The official Atlantic hurricane season spans June 1 through November 30, but nature does not always obey our arbitrary boundaries.  On average, about 97% of tropical cyclone activity falls within the official hurricane season, while the remaining 3% is spread out among the six off-season months.  Looking back to 1851, only two known storms have formed during January: Hurricane #1 in 1938 (formed January 3), and Subtropical Storm #1 in 1978 (formed on January 18).

The low pressure system shown in the satellite image above is mostly located in the middle and upper parts of the atmosphere, with just a hint of a presence at the surface.  The surface low is centered near 24N 42W, and as of 7 am EDT this morning, it was analyzed at 1010 mb (29.82″).

Surface analysis from 1200 UTC today. (NOAA)
Surface analysis from 1200 UTC today. (NOAA)

Every model I looked at develops this in the short term, and although it may not meet the structural requirements for a tropical cyclone, it could easily meet the requirements for a subtropical cyclone (what is a subtropical cyclone?).  Conditions should remain marginally favorable for this system to maintain itself for about the next 4-5 days before it gets absorbed into a mid-latitude front.

If this system does acquire enough organization and surface winds increase to 40 mph, it would earn the first name on the 2014 list: Arthur.  It is not and will not be a threat to land.

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Jason Samenow · January 13