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Earth from Orbit: Hurricane Sam Powers Across the Atlantic

September 30, 2021

As Hurricane Sam churns in the Atlantic Ocean, NOAA satellites are carefully monitoring the powerful Category 4 storm, the strongest of the 2021 Atlantic hurricane season to date.

Tropical Storm Sam formed on Sept. 23 in the eastern tropical Atlantic as the 18th named storm of the 2021 Atlantic hurricane season. Only the 2020 Atlantic hurricane season had more named storms by this date, with 23. Sam rapidly reached hurricane status on Sept. 24 and intensified into a Category 4 hurricane by Sept. 25. Sam is the fourth major hurricane (Category 3, 4 or 5 on the Saffir-Simpson Hurricane Wind Scale) of the 2021 Atlantic hurricane season.

Just three days after becoming a named storm, Sam peaked in strength on Sept. 26 with sustained winds of 155 mph. Not only did this make it the strongest storm of the 2021 Atlantic season to date, but meteorologists noted that it is very rare for a Category 4 or 5 hurricane to form that far east or south this late in the season. The only other hurricane on record to do so was Lorenzo in 2019. Sam’s rate of intensification was the highest on record that far east in the Atlantic this late in the calendar year. 

Sam has undergone several cycles of strengthening and weakening but has remained a major hurricane since Sept. 25. NOAA satellites observed Sam’s rapid intensification through bursts of convection and the presence of a defined, stable eye. Additionally, GOES-16 (GOES East) captured significant lightning activity within the eyewall during rapid intensification. 

NOAA satellites provide important information on the structure of a tropical system. The convective activity, in particular, is important for diagnosing the state of a storm. A lot of convection combined with the development of a clear hurricane eye help indicate rapid intensification. Conversely, satellites can tell a storm is weakening when cloud top temperatures increase quickly over a broad region and when the eye becomes less defined. 

The National Hurricane Center expects Sam to remain a major hurricane for several more days. Though Sam is not forecast to make landfall, large swells generated by the hurricane are affecting the Leeward Islands and will spread to portions of the Virgin Islands, Puerto Rico, Hispaniola, the Bahamas, and Bermuda by late this week. Significant swells will likely reach the East Coast of the United States and Canada by the weekend. These swells will likely cause life-threatening surf and rip current conditions.