Tropical Storm Arlene takes forecasters by surprise

Tropical Storm Arlene formed Thursday in the far-off Atlantic, defying stunned forecasters to become the first tropical cyclone of 2017 and only the second named storm in the satellite era to develop in April.

Arlene, which is not a threat to the U.S., beat the official June 1 start of hurricane season by more than a month, growing from a subtropical depression hundreds of miles west of the Azores that meteorologists gave little merit.

“I have to add one more surprise to my long hurricane forecasting career,” said National Hurricane Center specialist Lixion Avila, who was on duty Thursday. “Unexpectedly, the subtropical cyclone became a tropical depression this morning, and then it intensified to a tropical storm.

Check The Palm Beach Post’s storm tracking map.

As of a 5 p.m. advisory, Arlene was estimated to have 45-mph winds and was traveling west-northwest at 25 mph. Tropical storm-force winds extended out 105 miles from its center.

The unusual storm is expected to be short-lived, dissipating today as it is absorbed by a large mid-latitude low-pressure system.

But it will go down in the record books just the same.

Phil Klotzbach, a hurricane researcher at Colorado State University, said the only other April tropical storm on record since satellites became of use in the Atlantic basin — in the early 1970s — was Tropical Storm Ana in 2003.

Tropical depressions have been recorded in April in 1973 and 1981. And there was an April subtropical storm in 1992.

Storms that form early in the year outside of the deep tropics are not a foreshadowing to a busier hurricane season, Klotzbach said.

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“Generally, activity before Aug. 1 doesn’t correlate with the remainder of the season,” Klotzbach said. “The only exception is if we get tropical cyclone activity in the deep tropics prior to Aug. 1. Then, look out, it’s probably going to be a very active season.”

Klotzbach is predicting a slightly below-average 2017 hurricane season based on the tentative forecast for a weak to moderate El Nino by late summer/early fall.

This is the second consecutive year where hurricane season started early. The 2016 season got a jump-start when Hurricane Alex formed Jan. 14.

The incredibly rare storm that gained hurricane status hundreds of miles south of the Azores, was called “remarkable” by NHC forecasters who noted that since 1851, just one previous hurricane had formed in January.

Tropical Storm Bonnie followed Alex’s early lead, forming May 28. Tropical Storm Colin waited until the official start of the season when it was named June 5.

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