TS Arlene? Potential North Atlantic Cyclone Could Be 3rd Out-Of-Season Storm In 15 Months

[hatrack]

EDIT

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(A persistent swirl of disorganized clouds in the Central North Atlantic — continuously re-charged by frontal systems sweeping down from Baffin Bay and feeding on warmer than normal sea surface temperatures may become the first tropical cyclone of 2017. If it later forms into a tropical storm, it will become the third out-of-season named storm to form in the Atlantic over the last 15 months. Image source: LANCE MODIS.)

Last year, extremely warm sea surface temperatures combined with this kind of observed instability to spur the formation of Hurricane Alex during January. Tropical storm Bonnie also formed out of season during May. Similar very warm ocean conditions then helped to kick-start the late November formation of Category 3 Hurricane Otto (though November is still technically hurricane season, it’s supposed to be very rare to see so strong a storm form so late in the year).

Fast forward to April of 2017. According to the National Hurricane Center, there’s now a 30 percent chance that a tropical depression may form in the Central Atlantic over the next 48 hours. Ultimately, such a system could gather into the first Atlantic named storm of 2017 — Arlene. Such an event would mark the third time in just 15 months that the Atlantic basin had produced an out-of-season tropical storm or hurricane.

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(A vast majority — 97 percent — of tropical storms and hurricanes in the Atlantic form during hurricane season from June 1 to November 30. That said, human forced climate change may now be in the process of providing more fuel for the formation of out-of-season storms. Image source: North Atlantic Tropical Cyclone Climatology.)

Incidence of out-of-season tropical storms or hurricanes in the Atlantic is rather rare. Over 158 years from 1851 to 2009, perhaps one such system formed, on average, each year. Moreover, these storms primarily formed during May — which by itself produced more out-of-season storms than December through April combined. And a vast majority of these systems were tropical storms — not hurricanes or major hurricanes. In 2016 and 2017, Alex formed as a hurricane during January — which is practically unheard of. Bonnie formed during late May, which was less unusual but still out-of-season. Otto formed as a category 3 major hurricane during late November — another anomalous event. Meanwhile, if Arlene forms this April it will represent 1 out of only about 20 such systems that formed during the month in the period of 1851 through 2009.

EDIT

https://robertscribbler.com/2017/04/17/north-atlantic-may-cough-up-another-out-of-season-tropical-cyclone-this-week/#comments

[nitpicker]

1. Still no name

Maybe because it's about to be absorbed by a larger weather feature.