A messy situation developed off the Florida coast this weekend slam packed with pounding rain and impressive rainfall. It was spinning, and had rain bands, kicked up high surf, rip currents and beach erosion…and we’re still in Hurricane Season…so why wasn’t this considered a Tropical System?
* A tropical system must form in the Tropics. The area known as the tropics is defined as a region near the equator between 23° 26′ 16″ (or 23.4378°) N and the Tropic of Capricorn in the southern hemisphere at 23° 26′ 16″ (or 23.4378°) S. The system that affected Florida and now Georgia, South Carolina and the FL Panhandle had very strong winds….gusting to between 50-60 mph near Cape Canaveral, FL and up to 80 mph on a tower reported at 60 feet off the ground. These are very much strong enough to be considered Tropical Storm strength!
*Within the birth of a tropical system, they are born in areas that are considered “Barotropic”, meaning an area of temperatures that are all the same. Areas near the equator and close to the ITCZ (but not IN) or Intertropical Convergence Zone are considered Barotropic. Florida can be affected by fronts…which come off of land. These are areas considered “Baroclinic”. Baroclinic infers differing weather in terms of temperature, air pressure and moisture content. The Low that formed over Florida this weekend developed from an area of low pressure that has also been influenced by an area of high pressure well to the north of it.
In the instance of the Florida Low, some of the wind strengthening was due to a Pressure Gradient Force. Essentially, winds around a Low move counterclockwise, whereas to the north where an area of high pressure was present, winds moved clockwise around it. You can picture this as creating a tunnel effect, with winds speeding up in between the area between the two differing areas pressure. This is why it was so breezy in the Wiregrass over the weekend.
*Next….a tropical system is considered a “Warm Core System” where the central pressure is lowest in the middle and at the surface and weakens the higher you go up in Altitude. The sloppy Low pressure system moving across Florida into Southern Georgia has displacement. This means that the strongest winds are located near the area of lowest pressure, or at the center, which hasn’t been the case with this system.
*Tropical systems often have symmetry. The different quadrants often look very similar to each other…where as extra tropical system although rotating, often represent an elongated comma.
So in summary, this Extratropical Low has produced Tropical Storm rainfall totals between 4.5″-10″, wind speeds between 40-60 mph with 60+ mph gusts, tornado watches in the areas of greatest wind shear, and moderate beach erosion and rip currents…..but will not become a named system due to the differing characteristics listed above.
SO…contrary to the popular metaphor, If it walks like a duck, talks like a duck and eats like a duck…..it’s NOT necessarily a duck :)