Hurricane Gaston (2016)

**Hurricane Gaston** was a long-lived Cape Verde-type hurricane with little impact on land. The seventh named storm, third hurricane, and first major hurricane of the active 2016 Atlantic hurricane season, Gaston brought minor impacts to the Azores. Gaston peaked as a category 3 hurricane with maximum sustained winds of 120 mph and a minimum pressure of 955 mbar on two separate occasions.

## Meteorological History

On August 17, the National Hurricane Center (NHC) began monitoring the possibility of a tropical wave developing in the eastern tropical Atlantic over the common days. Chances were lowered slightly the next day, but eventually were increased once again. The tropical wave emerged into the Atlantic ocean on August 21. At 12:00 UTC on August 22, with organized deep convection and a closed circulation present, the wave developed into Tropical Depression Seven. Operationally, it was designated a tropical depression until 21:00 UTC that day. Six hours after formation, the depression strengthened into Tropical Storm Gaston. After becoming a tropical storm, Gaston developed a low-level eye feature and began to intensify. By 12:00 UTC on August 23, Gaston was a strong tropical storm with winds of 65 mph. Gaston's intensification slowed later that day due to a tongue of dry air from the Saharan Air Layer, but intensification resumed the next day when Gaston became a hurricane at 12:00 UTC August 24. Operationally, it was not upgraded into a hurricane until early on August 25, when a Global Hawk mission found hurricane-force winds.

Shortly after becoming a hurricane, wind shear around Gaston increased as Gaston moved near an upper-level low, and Gaston began to weaken as it took on a disheveled appearance. At 12:00 UTC on August 25, Gaston weakened to a strong tropical storm. Gaston then weakened further later that day to a tropical storm with maximum sustained winds of 65 mph. For the next day, Gaston changed little in intensity as it took on an appearance somewhat resembling a subtropical cyclone due to its interaction with the upper-level low. Early on August 27, as Gaston began to move away from the upper-level low, wind shear decreased, and Gaston began to improve in structure. By 18:00 UTC on August 27, Gaston had regained hurricane strength as its structure continued to improve.

After becoming a hurricane for a second time, Gaston developed a new closed eye feature and began steady intensification. By 12:00 UTC on August 28, Gaston became a category 2 hurricane, and at 18:00 UTC that same day, Gaston strengthened into a category 3 hurricane - making it the first major hurricane of the 2016 Atlantic hurricane season. Gaston then reached its initial peak intensity as a category 3 hurricane with maximum sustained winds of 120 mph and a minimum pressure of 955 mbar at 00:00 UTC on August 29. Shortly after Gaston reached its peak intensity, an eyewall replacement cycle began and the slow-moving cyclone suffered from cold water upwelling. As a result, Gaston weakened below major status by 12:00 UTC on August 29, and remained a category 2 hurricane for the next 36 hours. However, the next day, Gaston began to accelerate to the northeast at a faster pace, and the eyewall replacement cycle had been complete. Gaston then developed a very large eye and took on a shape resembling an annular hurricane. The hurricane acquired its secondary peak intensity at 00:00 UTC on August 31 as a category 3 hurricane with maximum sustained winds of 120 mph and a minimum pressure of 955 mbar - the exact same intensity as its first peak.

Gaston maintained an impressive appearance for the next day or so, but as it began to reach cooler waters and stronger shear by August 31, weakening ensued as the cyclone began to move northeastward towards the Azores. A Tropical Storm Warning was issued for parts of the Azores around this time. By late on September 1 as water temperatures fell below 26 degrees Celsius (the typical threshold required for tropical cyclone development), Gaston began to lose deep convection and its circulation became exposed. At 12:00 UTC on September 2, Gaston weakened below hurricane intensity as it neared the Azores, and 6 hours after weakening to a tropical storm, Gaston became a post-tropical remnant low as it became devoid of deep convection. Impacts in the Azores were very minor, no major damage or deaths were reported. Operationally, Gaston was not declared a remnant low until 09:00 UTC on September 3.