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Sam could remain a major hurricane into the weekend and pass close to Bermuda

The storm peaked Sunday just shy of Category 5 strength

Satellite view of Hurricane Sam on Monday. (NOAA)
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Roughly one month ago, Hurricane Ida peaked at high-end Category 4 strength, slamming into southeast Louisiana. Hurricane Sam topped Ida’s ferocity over the weekend as it put on a dizzying display of strength for weather satellites. But, unlike its predecessor, the storm steered clear of land.

The storm weakened Sunday night but remained a major (Category 3 or higher) hurricane early Monday while undergoing some structural changes. It is expected to pass harmlessly north of the Leeward Islands through midweek but could affect Bermuda this weekend. Residents in Atlantic Canada should also keep a close eye on the system for possible impacts by early next week.

On Sunday, Sam was the most powerful system anywhere on Earth, resembling an atmospheric buzz saw. It became the fifth storm of the Atlantic hurricane season to rapidly intensify or see its peak winds increase at least 35 mph in 24 hours. And it marked the fourth hurricane of 2021 rated Category 3 or higher. 2021 is the sixth year in a row with above-average tropical activity, thanks to Sam and the onslaught of previous storms.

The storm’s winds peaked at 155 mph on Sunday afternoon (Ida’s winds peaked at 150 mph), just 2 mph shy of Category 5 strength. It took just three days for Sam to strengthen from a fledgling tropical storm to a high-end Category 4. When it neared peak strength Sunday afternoon, lightning erupted within its eyewall, the ring of intense thunderstorms surrounding its calm center.

Its rate of intensification was the highest on record that far east in the Atlantic this late in the calendar year, according to Sam Lillo, a researcher at the National Oceanic and Atmospheric Administration.

Most major hurricanes undergo rapid intensification at some point in their life cycles, but the frequency of such strengthening has been increasing, and studies have connected the increase to human-caused climate change.

Forecasters are also monitoring at least two other tropical waves that are likely to develop into named storms and potentially hurricanes. That would exhaust the 2021 list of storm names and, for the second straight year and only the third time on record, force forecasters to draw additional names from an alternative list.

Weather panel ends use of Greek names for Atlantic hurricanes, retires deadly 2020 storms

Sam, currently

As of 11 a.m. Eastern time Monday, Sam was a Category 3 hurricane with winds of 125 mph as it moved northwest at 8 mph. It was located 745 miles due east of the northern Leeward Islands but is expected to pass well to their north. On satellite, Sam appeared less symmetrical compared with the weekend, when it was close to Category 5 intensity.

Sam was undergoing what’s known as an “eyewall replacement cycle,” in which the ring of intense thunderstorms surrounding its center was reorganizing. Its eye had disappeared on satellite, though a warm spot was visible where sinking air was working to clear it out once again. This could lead to another round of intensification.

Sam is a compact storm; hurricane-force winds topping 75 mph barely extend 30 miles outward from the center. That means the storm is susceptible to quick pulses up and down in strength. Although Sam may have weakened briefly, there’s no reason it can’t consolidate and organize quickly once again, and the National Hurricane Center is calling for the storm to remain a major hurricane into the weekend.

The forecast for Sam

By the middle of this week, Sam will curl to the north along the western periphery of a ridge of high pressure parked over the open Atlantic. The high-pressure zone stretches from the Azores to near Bermuda. The strength and exact location of the high-pressure dome will determine where exactly Sam goes, since the high acts as a guardrail of sorts.

While the East Coast of the United States is in the clear, Bermuda could find itself near the path of the storm. Larry passed just east of Bermuda, and there’s a chance that Sam could do the same, but its exact position on its closest approach is very uncertain.

Sam will make its closest pass to Bermuda this weekend, and predicting the track and intensity of hurricanes five or more days out is far from an exact science; in fact, forecast tracks err by an average of 200 miles five days into the future; Bermuda is only about 21 miles long and 1.75 miles wide at its widest point.

Also, the storm is relatively compact, so it would require almost a direct hit for hurricane-force winds to intercept Bermuda. The latest model tracks take Sam east of the island territory, but shifts are possible and the storm should be closely monitored.

Well down the road, there is the potential that Sam could be tugged west toward North America by low pressure over the eastern United States. That could result in some concern for the Canadian Maritimes, particularly between Oct. 4 and 6.; that said, nearly 10 days remain, and enormous uncertainty abounds, as shown by the spread of model simulations in the above map.

Elsewhere in the Atlantic

Only two storms remain on the Atlantic’s 2021 conventional naming list — Victor and Wanda. A pair of tropical waves, one in the central tropical Atlantic and another off the coast of Sierra Leone, are likely to develop into named storms; the Hurricane Center assigns them 80 percent odds of developing. That would consume the remainder of the list.

It’s becoming late in the season for storms to track across the Atlantic’s MDR, or main development region; that’s the belt of tropical waters between Africa and the Lesser Antilles. That said, the two systems behind Sam bear watching as they make their way west over warm ocean waters in the coming days.

This year, the Hurricane Center will be moving on to a supplemental list of names rather than assigning Greek letters as names. This is the first year that is the case. Adria, Braylen and Caridad are first up on that list.

The remnants of Tropical Storm Peter could also reacquire tropical or subtropical characteristics east of Bermuda.