Tropical Storm Sam underwent rapid intensification and became the seventh hurricane of the 2021 Atlantic tropical season on Friday morning. Sam has continued to rapidly strengthen and is now a Category 4 monster hurricane with sustained winds of 145 miles per hour. AccuWeather forecasters warn that there is a risk that the hurricane could turn toward the United States during the first few days of October after it navigates near the Leeward Islands early this week.
Sam was a Category 1 hurricane with maximum sustained winds of 75 mph on Friday morning, which was an increase of 40 mph in less than 24 hours. Meteorologists define rapid intensification as an increase in a storm’s maximum sustained winds of 35 mph or more within 24 hours, and Sam surpassed that benchmark.
By Saturday morning, the maximum sustained winds had increased to 120 mph, making it a Category 3 storm. Once a storm reaches category 3 status, it is considered to be a major hurricane. By Saturday afternoon, Sam strengthened further to 140 mph, making it a Category 4 storm.
The cyclone’s development wasn’t showing any signs of slowing down any time soon. High-level clouds were seen fanning out away from the storm on satellite images, which indicated strong outflow and what meteorologists refer to as “venting.”
“This venting signature is typical of an intensifying hurricane,” AccuWeather Hurricane Expert Dan Kottlowski said. He added that the counter-clockwise orientation of the clouds gives Sam a “classic Cabo Verde hurricane,” which is a type of hurricane that forms in the eastern Atlantic near the Cabo Verde Islands. This type of hurricane can go on to become some of the strongest, longest-lived hurricanes in the basin.
Sam was located 940 miles to the east-southeast of the northern Leeward Islands and was moving west-northwestward at 8 mph. A sweeping area of Saharan dust associated with dry air was visible near Hurricane Sam in satellite images on Friday. Dry air and dust can often act as inhibiting factors for tropical cyclone development, but Sam’s rapid intensification had so far defied those elements.
“There’s still lots of dry air associated with or in the path of Sam, but what it’s doing is, in a sense, creating its own environment for it to develop,” AccuWeather Chief On-Air Meteorologist Bernie Rayno said. “None of the dry air is coming in toward the storm’s center itself. Instead, it’s being pushed outwards away from the system, and, with little wind shear, that is light winds aloft, we expect Sam to continue to develop.”
As Sam strengthens, the hurricane will produce progressively larger swells that will propagate outward from the center. These swells will generate building seas ahead of the storm that will cause large waves and rough surf along the east- and northeast-facing shores of the Leeward Islands that have direct exposure to the Atlantic.
“Sam has become a major hurricane Saturday morning and is expected to continue to strengthen on Sunday,” AccuWeather Senior Meteorologist Rob Miller said Saturday morning.
Sam is predicted to begin a gradual turn more toward the north, which will take the hurricane on a northwestward path on Sunday. Precisely when Sam makes that turn will be critical in determining exactly how much impact the strengthening cyclone will have on the Leeward Islands.
The sooner Sam begins to track to the north the more likely the hurricane’s dangerous eyewall, with its destructive winds, will avoid the islands on Monday and Tuesday. With an earlier northward turn, the outer rain bands from the storm would bring brief heavy, gusty squalls with rough seas and surf to the islands.
However, if Sam waits a few days to begin curving northward, then there is the potential for harsher impacts to the Leeward Islands, including stronger winds, coastal erosion from pounding waves and flooding rain that can bring substantial risk to lives and property.
Beyond a potential close encounter with the Leewards, Sam will either continue to turn progressively to the north or continue along on a west-northwest track later this week, which would take the hurricane closer to the U.S.
At this point, AccuWeather forecasters say a due west path through the northern islands of the Caribbean seems unlikely. However, there is still potential for Sam to drift toward the U.S. or toward Bermuda and Atlantic Canada.
The weather pattern over North America could dictate how close Sam approaches the U.S., Rayno explained.
If a southward dip in the jet stream sets up off the East Coast, then there is a good chance that Sam will be steered away from the U.S. “But, if that jet stream dip sets up farther west or meanders westward, then there is room for Sam to get very close to the U.S. next weekend,” Rayno said.
