Hurricane Sam Didn't Strike Land, But Tenaciously Hung Onto Its Major Intensity (RECAP)

Sam became the eighteenth named storm of the 2021 Atlantic hurricane season on Sept. 22 while it was about 2,000 miles east-southeast of the Leeward Islands, closer to Africa.

Sam was the second earliest "S" storm in Atlantic Basin history, behind only 2020's Sally, according to NHC hurricane specialist Philippe Papin.

Less than 36 hours later, it became the season's seventh hurricane, and by the morning of Sept. 25, it had rapidly intensified into the fourth major hurricane of 2021. Maximum sustained winds in Sam increased from 85 mph to 140 mph in the 24 hours ending Sept. 25, 5 p.m. EDT.

The powerful, yet small, hurricane continued to gain strength and reached a maximum intensity of 155 mph while spinning several hundred miles to the east-southeast of the Leeward Islands, according to a Sept. 26 Hurricane Hunter reconnaissance mission.

Sam joined 2019's Hurricane Lorenzo as the only Category 4 or stronger hurricanes so far east this late in the hurricane season, according to NOAA-CIRES researcher Sam Lillo.

Sam weakened temporarily because of an eyewall replacement cycle, a process in which an intense hurricane replaces its eyewall with an outer eyewall.

Once that cycle was complete, an eye appeared again in infrared satellite imagery the following afternoon.

Sam would reach 150 mph maximum winds yet again by Oct. 1 as it was southeast of Bermuda.

Sam then accelerated into the North Atlantic Ocean well southeast of the Canadian Maritimes and became a powerful post-tropical cyclone on Oct. 5 about 1,100 miles southwest of Reykjavik, Iceland.

High surf and rip currents were the only indirect impact of Sam along the U.S. East Coast, just as Hurricane Larry generated in early September when it also passed east of Bermuda.

Sam was a major - Category 3 or stronger - hurricane for just under 8 days in a row, the longest continuous stretch at that intensity in the Atlantic Basin since Ivan in 2004, according to Phil Klotzbach, tropical scientist at Colorado State University.

Klotzbach also found Sam was the fifth "longest lasting most intense" Atlantic hurricane, as measured by the ACE index, in records since 1966.

Perhaps the most noteworthy aspect to Sam was the penetration of its core by an uncrewed surface "Saildrone", the first ocean drone to ever penetrate a major hurricane. The drone captured video of 50-foot waves and winds over 120 mph on Sept. 30. (See video atop this article.)

A separate NOAA buoy also clocked wind gusts of almost 100 mph and up to 40-foot waves on Sept. 30.

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