Turbulent Mixing from Extratropical Storm Hermine

Hurricanes and their less intense derivitives (tropical and extratropical storms) are commonly discussed once they reach land due to the devastating impacts they have on coastal (and sometimes not even coastal) communities. However, to truly understand these storms we must look to where they form and generate their power, the ocean.

Hurricanes typically form in tropical regions of the oceans and are fueled by the evaporation of warm water from the ocean surface. As they move across the ocean, they gain strength by pulling more warm moist air from the ocean surface into the storm. The warmer the surrounding ocean, the stronger the storm.

Not only is it interesting to think of the impact of the ocean on the hurricane, but as the hurricane moves up the coast, the strong winds of the storm causes mixing at the sea surface.

In 2016, Hurricane Hermine formed in the Florida Straits in late August and was a Category 1 hurricane when it made landfall in the Florida Panhandle in early September. As it moved inland and up the coast, it weakened to an extratropical cyclone. About a week later it reached New England and passed over the OOI Coastal Pioneer Array.

As it passed over the Pioneer Array, wind speeds at the Inshore Surface Mooring jumped to 18 m s^-1 (40 mph!) with heavy rains (high precipitation). On the surface of the ocean, currents doubled in speed, water temperatures dropped, and salinity increased. At the nearby Upstream Inshore Profiler Mooring, warm surface waters were observed to have mixed downwards roughly 45 meters.