Week of May 22-28, 2005

It appears that the wet season has begun. Night-time temperatures have stayed above 70 degrees for the past week. This trend has been accompanied by a greater abundance of cloud cover in the afternoon and re-emergence of cumulonimbus clouds anvilling out at the top of the troposphere (bottom of stratasphere). So it looks like the south Florida summer rain machine is back up and running.

Typically we average somewhere around 2 inches of rain per week (or about 8-9 inches per month) during the wet season. However, the wet season never drops its rain uniformly throughout the summer, and each year the wet season seems to unfold in a slightly different pattern.

Last year we started the rainy season fast out of the gate with 20 inches in June. In the Big Cypress Basin, June is our most abundant rainfall month, averaging 10.6 inches of rain in June over the past 10 years. June consistently gets the most rain of any month because there is still a large amount of instability in the air from springtime fronts swooping down from the north and funnelling in moisture from the south.

Somewhere in July a less active second phase of the wet season tends to take control. July is our least abundant summer rainfall month, averaging 7.4 inches over the past 10 years in the Big Cypress. This dip in rainall is caused by the presence of more homogeneous atmosperic conditions up north, which tends to bring more stability and less rain to the south Florida weather machine. Other factors such as the position of the Bermuda high (which steers the directionality of the easterly trade winds blowing across the peninsula) and upper atmospheric warming are also at play.

As the summer progresses and sea breezes from both coasts collide with increasing severity in the middle of the peninsula, the localized convectional showers of the early wet season season give way to convergence fronts that form immense cells of storm clouds that can drop heavy amounts of rain over large areas, hitting the preserve first then moving on towards Naples. These convergence storm fronts mark the third phase of the wet season. (These are the really impressive, and often very scary storms). Some old-timers consider the onset of the convergence storms to be the start of the rainy season, even though these things don’t start up in earnest until late July or August. The months of August and September have averaged 8.3 and 8.9 inches of rain, respectively, over the past 10-years for the Big Cypress.

The fourth and final hurricane phase of the wet season tends to become a factor from August through October. South Florida seems to get the heaviest drenching from tropical storm activity (waves, tropical storms, and hurricanes) in September and October, but these events are hit and miss and more difficult to predict than the first three phases of the wet season. The 1998 wet season seemed to be over by mid October only to be hit by almost a foot of rain by Hurricane Mitch at the start of November. The same thing happened last year with Wilma.

Let’s all hope for a less eventful fourth phase of the wet season this year.

Regards,
Bob

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