Arlene (2017)

A non-tropical low in the central North Atlantic evolved into a subtropical depression on April 19, 2017 about 850 nautical miles southwest of the Azores, then transitioned to a tropical cyclone early on April 20. The system moved generally northeastward and then northwestward while orbiting a larger extratropical low, was a tropical storm from April 20–21, became extratropical again around 1200 UTC April 21, and dissipated by about 1800 UTC April 22 roughly 1,000 n mi west‑southwest of the Azores.

Arlene did not make any landfalls. It remained well offshore in the central Atlantic and produced no coastal watches or warnings.

The storm reached a peak sustained wind of 45 knots (about 52 mph) and a minimum central pressure of 990 mb at 0000 UTC April 21, equivalent to a moderate tropical storm (below hurricane strength).

There were no reports of storm surge or measured rainfall impacts on land associated with Arlene; no ships or land stations reported tropical‑storm‑force winds or notable surge values, and no rainfall totals at populated locations were recorded in the post‑storm data.

No deaths or damage were reported. The storm’s main significance is meteorological: Arlene was only the second tropical storm on record in the Atlantic to form in April (the other was Ana in 2003).

Forecast products noted limited lead time before genesis (a Special Tropical Weather Outlook was issued about 30 hours beforehand) and, because Arlene was short‑lived, official track and intensity forecast errors for the small sample of forecasts were larger than recent 5‑year means; several model guidance packages outperformed the official intensity forecasts.