Tropical Storm Sam formed Thursday in the Atlantic Ocean — the 18th named system in a bustling season — and is expected to intensify into a hurricane by this weekend.
The storm had strengthened throughout the day with maximum sustained winds of about 70 mph as of 11 p.m. EDT with additional strengthening expected, the National Hurricane Center said. The storm was centered about 1,560 miles east-southeast of the northern Leeward Islands and was moving west about 15 mph.
Sam could whip up into a major hurricane before approaching the islands of the northern Caribbean next week. "Sam is rapidly intensifying, and maximum sustained winds have increased," the Hurricane Center said, adding: "rapid intensification is forecast to continue through early Saturday. Sam is likely to become a hurricane very soon and then could be a major hurricane by Friday night or early Saturday."
Tropical storms become hurricanes when maximum sustained winds hit at least 74 mph, meaning Sam is nearly at hurricane strength.
The storm was expected to take a west to west-northwest track across the central Atlantic over the weekend, Accuweather said. Whether it makes landfall is still uncertain, but forecasters urged Bermuda, the Bahamas and the U.S. East Coast to stay vigilant.
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Most computer model forecasts show Sam swirling away from the East Coast late next week, weather.com said, because of a Bermuda high over the Atlantic and a southward plunge of the jet stream that could drive Sam north and northeast instead of westward toward the U.S.
Sam could also mimic Hurricane Larry earlier this month and kick up dangerous surf and rip currents along the Eastern Seaboard, forecasters said.
Two other systems, tropical depressions Peter and Rose, have both fallen apart. But Odette, a storm that first formed off the East Coast last week, could regain tropical storm status over the open waters of the north Atlantic, Accuweather said.
Tropical Storm #Sam has formed in the eastern tropical Atlantic - the 18th named storm of the 2021 Atlantic #hurricane season to date. Only 1 season on record has had 18+ Atlantic named storms by 23 September: 2020. 2020 had 23 named storms by 23 September. pic.twitter.com/AGFg37ljxw
— Philip Klotzbach (@philklotzbach) September 23, 2021
Sam is the 13th named storm to form in the Atlantic since Aug. 11, according to Colorado State University hurricane researcher Phil Klotzbach. And only one other hurricane season on record has had 18 named storms by Sept. 23, he said: 2020 had 23 named storms by that date.
So far this year there have been six hurricanes and three major hurricanes (Category 3 or stronger): Grace, Ida and Larry.
In August, the National Oceanic and Atmospheric Administration released its updated hurricane season forecast for the year: seven to 10 hurricanes; 15 to 21 named storms.
Track Tropical Storm Sam's path
This article originally appeared on USA TODAY: Tropical Storm Sam forms, forecast to become a hurricane by Friday