Satellite loop of what could be the first named storm of the hurricane season. (NOAA)

A swirl of clouds and low pressure out in the middle of the Atlantic is starting to look like something we usually see in June — the first named storm of the hurricane season. It’s becoming more organized and might even get a name — Arlene — on some time this week. As of Wednesday, it’s just a depression.

Historically, we’ve defined hurricane season as June 1 to November 30. But this will be the sixth “early” storm in the past six years.

The National Hurricane Center has been tracking this windy area of storms for several days but it’s only recently started to look more like a storm and less like a blob. It is very likely that if this low gets named, it would be a classified as a subtropical storm. At the moment, it is merely a Subtropical Depression One — not strong enough for a real name. The system is located about halfway between Bermuda and the Azores and is not a threat to land.

There is a spectrum of cyclone types, but they are coarsely grouped into three types based on their structure: nontropical, subtropical and tropical. As you might surmise, a subtropical cyclone is a hybrid of the other two, exhibiting some characteristics of an nontropical cyclone and some of a tropical cyclone.

Regardless of if it gets named, it will not be around for long and will not have the opportunity to intensify much. A strong mid-latitude trough is approaching from the west and this relatively weak low pressure will merge with the trough and be unrecognizable by the weekend.

Climatologically, it would be early to see the first named storm form but far from a record. In 2016, Subtropical Storm Alex formed on Jan. 13. Since 1966, when geostationary satellite data became available, the average date of first storm formation is June 22, but there is a lot of variability.

The official hurricane season — which runs from June 1 through Nov. 30 — is not intended to encompass all tropical cyclone cyclone activity, just a large majority of it. In fact, the data shows that the date of first named storm is getting earlier.


Time series of the date of first named storm formation in the Atlantic basin, from 1966-2016. (B. McNoldy)

If this system is named, it would be the sixth preseason formation in the past six years — the others were Alberto and Beryl in 2012, Ana in 2015, then Alex and Bonnie in 2016.

The name Arlene is still in circulation from the original batch of names and goes back to 1981 (this year will be its seventh use).