Tropical Storm Isaias, a cyclone in the Gulf of Mexico, is expected to strengthen into a hurricane by Thursday, according to the U.S. National Oceanic and Atmospheric Administration. If it does, Isaias would be the latest-forming first hurricane in the Atlantic season since reliable records began.

As of Wednesday morning, Isaias sat about 260 miles (420 kilometers) off the coast of Progreso, Mexico, and NOAA forecast that it is headed toward the U.S. Gulf Coast, including parts of Mississippi, Alabama and Florida.

Isaias’s winds are up to some 45 miles per hour (75 kilometers per hour) as of this writing. To be considered a hurricane, winds must hit or surpass 74 mph (119 kmh).

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If Isaias makes landfall as expected, the storm will likely bring strong gusts and heavy rainfall, with the potential for flash flooding and dangerous storm surge, says Jennifer Tate, a meteorologist at NOAA’s Weather Prediction Center.

As Scientific American previously reported, hurricane activity in the Atlantic typically begins in June and peaks in September. But this year the region has been quiet—with no hurricanes all season. Soon-to-be Hurricane Isaias would mark a historically late arrival for the first hurricane of the season.

The quiet is in part linked to El Niño, meteorologists say. In an El Niño year, waters in the Pacific are unusually warm. This can drive global weather patterns, including in the Atlantic Ocean. There high vertical wind shear—changes in wind speed or direction with altitude—typically make it difficult for hurricanes to form during El Niño years.

“It is common during El Niño patterns for the Atlantic to be quieter in terms of hurricanes,” Tate says, “whereas the eastern Pacific, and the Pacific in general, is more active. And we have seen that this year.”

Indeed, in the Pacific, hurricanes have threatened Hawaii to an unusually high degree this season.

For those on the Gulf Coast, Tate recommends staying up to date on hurricane forecasts, getting prepared with food and supplies in the case of a power outage and following any local evacuation orders.

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