ORLANDO, Fla. – Very early Thursday morning, the National Hurricane Center has put Florida underneath a yellow formation cone once again.
A weak disturbance is currently located off our southeast shores, with some subtle counter-clockwise rotation with it.
While development chances are fairly low for the time being, we’ll have to see what takes shape into this weekend. Regardless, we’re in for some hearty rain totals because of the system itself and its combined efforts with high pressure steering moisture in from the west Atlantic.
There’s a bit more to this set up than meets the eye.
Hurricane season tends to come in different phases.
At the beginning of the season, June, we’re faced with a combo of mechanisms that drive where and when our named storms begin to develop. We call this segment the “home-grown” portion of the season.
Then as we wander through July and early August, things typically quiet down some. Primary reason for this quiet spell is the increase in our Saharan dust as the summertime hits hard across the equator, driving something called a “thermal” wind up across northern Africa.
This thermal wind is created strictly by temperature. The hot air helps develop a heat low over northwest Africa, and results in stronger winds at the surface and up to about the mid-levels of the atmosphere.
Combine that with scattered monsoon thunderstorms to the immediate south of our heat low, and that’s a recipe for all kinds of blowing dust. I used to see it during my time spent forecasting in the desert southwest. Afternoon thunderstorms would kick up huge dust storms called haboobs.
In this case, that same heat low picks up the dust and proceeds to hurl it across the west coast over the Atlantic where our easterly trade winds that linger throughout the year catch it and keep it moving across the tropics.
It’s presence is greatest from late June, through July, and then begins to taper during the first two weeks of August as moisture and rains really establish themselves over Africa.
Once we get into August, we usually call the peak season “Cabo Verde” season. This is when we get the very healthy tropical waves coming off Africa that mostly go on to become our tropical storms and eventually hurricanes.
Now, we’re faced with October. Cabo Verde season is winding down, as the intertropical convergence zone begins its fateful retreat back south with the introduction of the fall. We’ll still see some waves meandering westward through the tropics, but not nearly as frequently.
We end up with a mixed bag piece of the season. Cold fronts coming off the U.S. intensify as cooler air tries to come down. You mix these fronts with very warm waters, like we’ve got off both our east and west coasts right now, and things can start to spin.
We’re back to a portion of home grown season with a combined effort of our tropical waves still in play out over the Atlantic.
This first yellow blip, as I so eloquently describe them, is one of likely many as we go through October and early November. With more fronts and troughs reaching down from up north towards the Gulf and the west Atlantic ocean, the chances for more close-to-home low pressures grows once again.
That’s precisely what’s driving our gloomy weather over Central Florida Thursday.