Hurricane Hermine Bearing Down On Florida

It looks like Florida’s hurricane drought will come to an end after all.

After so much uncertainty about what was then Invest 99L – whether it would become a major hurricane or fail to make it to a tropical depression – it looks like Florida will see its first hurricane since Wilma stormed ashore southwestern Florida as a category 3 hurricane in 2005.

The most recent National Hurricane Center advisory at 11 pm EDT lists Hurricane Hermine as a weak category 1 storm with 80 mph sustained winds moving to the NNE at 14 mph. It was only 40 miles E of Apalachicola, FL, so it will make landfall on the “Big Bend” of Florida tonight. With a current pressure of 984 mb, it isn’t particularly deep (our strongest windstorms commonly approach 970 mb, and occasionally surpass 960), but because tropical cyclones are much more compact than the extratropical ones we experience here in the Pacific Northwest, wind speeds are often higher for a given central pressure, even if they aren’t as expansive. Moreover, tropical cyclones are generally much wetter than the windstorms that impact the Pacific Northwest, and the Gulf Coast of Florida will have to deal with a storm surge from Hermine that will be amplified by the bathymetry offshore. And if that wasn’t bad enough, hurricanes often spawn weak tornadoes when they make landfall. In fact, Florida currently has six seperate tornado warnings: Northeastern Dixie County, Central Dixie County, Lafayette County, Western Lafayette County, Western Orange County, and Southwestern Seminole County are all currently under tornado warnings. There’s no denying that Florida has its hands full with this storm.

Below is the current radar imagery for Hermine. Like all hurricanes, it will weaken rapidly as soon as it encounters land, as tropical cyclones derive their energy from warm ocean water. However, right now it is going strong, with intense rainbands pummeling the Sunshine State and a well-defined eye just offshore.

The latest aircraft reconnaissance shows a minimum pressure of around 985 mb, with peak sustained winds at 90 knots. However, it is important to remember that winds are higher aloft where the aircraft is flying than they are at the surface, and the minimum pressure of the storm itself is generally deeper than the minimum pressure estimated by the aircraft. Since the NOAA Hurricane Hunters are flying several thousand feet up, they have to estimate the surface pressure based on the temperature profile of the atmosphere, or environmental lapse rate, as the pressure measured by the aircraft itself was around 805 mb.

Hermine has already dropped a tremendous amount of rain over Florida, with some areas near Tampa having picked up over 10 inches of rain over the past three days. Also, note how shallow it is off the Gulf Coast of Florida. This helps to amplify the incoming storm surge, which could reach 9 feet along certain areas off the Florida Coast.

After Hermine sweeps through Florida, it will continue traveling northeastward, interacting with a weak cold front over Georgia and re-emerging over the Atlantic after it passes through the Carolinas. The interaction with the cold front will signal Hermine’s transformation to an extratropical cyclone but will allow it to keep tropical storm strength as it travels along land. After emerging over the Atlantic, Hermine may re-intensify into a hurricane as it travels over the warm waters of the Gulf Stream, but a small difference in track could result in a vastly different outcome, as the Gulf Stream is a relatively narrow current. As it continues its path northward along the Atlantic seaboard, it will slow down considerably as it interacts with a cut-off low, dawdling around in a drunken stumble and delivering several inches of rain to the Delaware, New Jersey, and New York Coasts. Thankfully, it should get swept out to sea before impacting New England to any significant extent.

Thanks for reading! I’ll keep you updated on Hermine as it transitions into an extratropical cyclone.