Hurricane Sam's epic Atlantic journey continues after an eyewall replacement cycle -- and it will make its presence felt in the U.S. with stormy seas and, potentially, coastal flooding.
Updated Sep. 29, 2021 11:31 PM EDT
Hurricane Sam is likely to continue its long journey as a major hurricane across the Atlantic Ocean into late this week. It will stay well out to sea and avoid direct impact on the United States, but AccuWeather forecasters warn that big waves will still reach the shores of the Atlantic coast. After a near-miss with Bermuda, the storm could swing a left toward the island of Newfoundland in Atlantic Canada.
For a couple of days as it strengthened again and through late Wednesday evening, Hurricane Sam was the most powerful storm on the planet. The Category 4 hurricane was packing 145-mph maximum sustained winds and churning 350 miles to the east-northeast of the northern Leeward Islands and moving northwestward at 12 mph.
Sam should be able to maintain major hurricane intensity status (Category 3 or higher) due to light wind shear and warm water along its projected path, according to AccuWeather Senior Meteorologist Adam Douty.
Sam strengthened back into a Category 4 storm Monday night into Tuesday after undergoing what meteorologists call an eyewall replacement cycle from Sunday night into Monday. This change in the structure of the inner core of the hurricane caused the eye to become more ragged-looking in satellite imagery, the central atmospheric pressure of the storm to rise and sustained winds to weaken slightly Monday.
Top winds in the core of the hurricane dipped to Category 3 strength at 120 mph for a time Monday, but by early Tuesday morning had increased to 130 mph, which was Category 4 intensity. Late Sunday afternoon, Sam had equaled the intensity of Hurricane Ida from August with maximum sustained winds of 150 mph, just 6 mph shy of Category 5 intensity.
Sam to stir US coastal waters
Sam's lone impact to the U.S. will be related to wave action. Even though the hurricane may never be closer than 500 miles or so away from the Eastern Seaboard, large swells generated by the storm will propagate outward and reach the Atlantic coast. When compared to Larry, wave action along the U.S. Atlantic coast will be significantly less, but not without some impact.
Sam is a much more compact hurricane than Hurricane Larry, which churned in the basin earlier this month and also stirred up dangerous surf along the East Coast. Hurricane-force winds extended outward 60 miles from Sam's center and tropical-storm-force winds reached out about 150 miles from the storm's core. At its peak, Larry was significantly larger than Sam. At one point, Larry's hurricane-force winds extended out 90 miles and tropical-storm-force winds reached outward 240 miles.
"Rough surf and strong rip current risk will impact the Atlantic coast of the United States from south to north beginning on Friday and continuing this weekend," Douty said.
Meteorologists continued to urge beachgoers to follow all restrictions set forth by local officials, especially due to the lack of lifeguards on duty this time of year.
It is possible that wave action may produce minor flooding at times of high tide in areas prone to taking on water during nor'easters.
The highest seas associated with Sam will likely remain in the zone from northeast of the Leeward Islands to near and east of Bermuda and southeast of Atlantic Canada. But, because of the potential for large swells produced by Sam, all cruise, fishing and shipping interests offshore of North America should keep abreast of forecasts.
Minimal impact forecast for Bermuda
After Sam produces large waves and dangerous surf for the exposed northeast-facing shorelines of the islands in the northeastern Caribbean Sea this week, the hurricane's next close encounter will be with Bermuda.
This image of Category 4 Hurricane Sam was taken around daybreak on Wednesday, Sept. 29, 2021. Sam was located several hundred miles to the east of the Leeward Islands at the time with a small but distinct eye. (CIRA at Colorado State/GOES-East)
Even though Sam may be stronger than Larry was as it passes to the east of Bermuda Friday night into Saturday morning, Sam's more compact nature may mean practically no impact from rain and wind on the islands. As Larry passed 190 miles east of Bermuda on Sept. 9, it was a Category 1 hurricane with 90-mph sustained winds, according to the NHC. Larry barely produced breezes and rainfall worthy of a tropical storm in Bermuda.
"At this time it appears the main impact to Bermuda will be rough surf and rip currents from late Thursday into Saturday as Sam passes to the east," Douty said, but he cautioned people on the islands to still pay attention to the forecast for Sam given its power.
AccuWeather meteorologists expect swells to reach the islands ahead of the storm's closest approach at the end of the week. These swells will lead to large breaking waves on the southern and eastern shorelines from Thursday to Friday and then the northern and western shorelines of the islands Saturday and Sunday.
If Sam's track were to shift farther to the west by 100 miles or more, then impacts from rain and wind would ramp up and become dangerous and damaging for Bermuda.
The islands of Bermuda are no stranger to encounters with hurricanes and tropical storms. However, on average, the islands experience a damaging tropical system only once every six to seven years, according to the Bermuda Weather Service. This year, even though Tropical Storm Ana, Hurricane Henri and Larry passed within a couple of hundred miles of the islands, there were minimal impacts.
Less than a dozen tropical systems have made landfall in Bermuda since the mid-1800s. In 2014, Fay and Gonzalo crashed ashore -- the only record of two landfalls in the same year. The strongest hurricane to hit the islands in modern times was Category 3 Hurricane Fabian in Sept. 2003. Fabian took the lives of several people, produced gusts to near 150 mph and generated a 10-foot storm surge.
Beyond Bermuda, Atlantic Canada still at some risk of impacts
As Sam pushes north of Bermuda, the hurricane will encounter progressively cooler waters that will cause it to lose some wind intensity and eventual transition to a non-tropical system. However, weakening will occur gradually, and it is possible the system could still pack hurricane conditions as it reaches waters offshore of Atlantic Canada and perhaps Greenland.
There is still some possibility that a developing southward dip in the jet stream that occurs over the northeastern U.S. and southeastern Canada throughout the week could capture and pull Sam westward.
"While this would not happen quickly enough to have an impact on the U.S., it could still pull the storm close to the island of Newfoundland later this weekend or early next week with heavy rain and gusty winds," Douty said. A period of rough seas will still affect Atlantic Canada this weekend regardless of Sam's exact track, he added.
Larry was the last hurricane to make landfall on the island of Newfoundland, the easternmost of Canada's provinces. Barring a westward loop over the island of Newfoundland, Sam could bring heavy rain, high winds and high-elevation snow to Greenland early next week, something Larry did as well.
There are additional tropical systems on AccuWeather meteorologists' radar. One of the two remaining names on the list for 2021 Atlantic Hurricanes, Victor, formed on Wednesday.
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