Rainy Season Starts!

National Weather Service Declares Start Of Rain Season

LABELLE, FL. -- As a result of the daily showers and thunderstorms over much of South Florida this week, as well as the expectation of additional rainfall during the next several days, The National Weather Service Miami Forecast Office has declared May 11 as the beginning of the 2009 rainy season. This is 9 days earlier than the median start date of May 20 (about one week later along the Gulf coast and the Lake Okeechobee region), and the earliest start to the rainy season since 2003.

The early start to the rainy season is quite welcome this year due to the extreme drought conditions being experienced over most of South Florida. The recently concluded dry season of 2008-2009 ranked as the second driest dry season on record for most South Florida locales, with only 1971 being drier.

Here are some rainfall totals and departures from normal (in inches) for the 2008-2009 dry season from November 1 to May 10:

SITE                         RAINFALL            DEPARTURE FROM Nov 1 ­ May 10    NORMAL

MIAMI INTL AIRPORT          4.66              -12.36
FORT LAUDERDALE INTL    4.74              -16.43
PALM BEACH INTL              6.79              -16.88
NAPLES REGIONAL            2.31              -10.40
IMMOKALEE                       2.95              -10.58
CLEWISTON                       2.38              -12.08
BELLE GLADE                    2.74              -12.39
MOORE HAVEN                  3.75              -11.94
MIAMI BEACH                     6.91              -9.15

The start of the South Florida rainy season is normally determined by a variety of factors, most notably the nearly daily presence of showers and thunderstorms on a diurnal cycle. This diurnal cycle typically consists of morning and early afternoon showers and thunderstorms over coastal and metro areas, followed by afternoon inland showers and thunderstorms, some which can become strong with frequent lightning, hail and gusty winds.

These afternoon showers and thunderstorms often move toward the metro areas of both the east and west coasts of South Florida. This pattern is caused by a warming and moistening of the lower and middle atmosphere as we approach the peak summer months, as well as a weakening of high pressure aloft which leads to greater atmospheric instability and promotes shower and thunderstorm development.

The showers and thunderstorms usually develop along the sea breeze which forms along both the Atlantic and Gulf coasts, as well as a lake breeze from Lake Okeechobee.

An average of 35-45 inches of rain falls over South Florida during the rainy season. This represents about 70 percent of the yearly rainfall. The outlook for this rainy season calls for an increased likelihood of wetter than normal conditions for the period from June through October.