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Record-breaking rainfall and flash flooding in Naples, FL on Aug. 4, 2014

Surface weather map at 5:00 p.m. E. D. T. on Aug. 4, 2014.  Weak low-pressure center over Florida contributed to heavy rainfall in Naples area.
Surface weather map at 5:00 p.m. E. D. T. on Aug. 4, 2014. Weak low-pressure center over Florida contributed to heavy rainfall in Naples area.

On Monday, Aug. 4, 2014, while Tropical Storm Bertha briefly gained hurricane status hundreds of miles from the east coast of Florida, a separate tropical weather system (Fig. 1 and Fig. 2) brought flooding rainfall to parts of Collier and Lee counties in southwest Florida (Fig. 3).

Flooding on Aug. 4, 2014 in the Industrial area just northeast of downtown Naples.  Here, a car is trapped in floodwaters.
H. Michael Mogil

This weak weather system (with well-above average values of atmospheric moisture) spawned widespread, relatively slow-moving tropical downpours across the area starting late Monday morning. Training of heavy storms added to the impressive rainfall totals. Rainfall rates at the Naples Municipal Airport (APF) for the better part of the period between 12:49 p.m. E.D.T. to 2:18 p.m. E.D.T. topped 4 inches per hour. For the one-hour and 29 minute period, a total of 5.18 inches fell. These values, according to Rob Molleda of the National Weather Service Miami Forecast Office, fall into a 50- to 100-year rainfall return period category. Statistically, this means that there is about a 1 to 2 percent chance of such intense, short-period, rainfall happening in any given year.

These rainfall rates taxed the ability of drainage systems, including roadway swales (a low-lying or depressed and often wet stretch of land), canals, streams and storm collection drains. As a result, many areas from downtown Naples northeast to the Industrial District near Airport Road and Golden Gate Parkway quickly flooded (Fig. 4, Fig. 5, and Fig. 6). Flood waters reached bumper level on many parked cars, numerous cars were stalled out or otherwise stranded in rapidly rising flood waters, and many roadways were closed or impassable due to the flash flooding.

Rainfall totals near and just northeast of downtown Naples approached around 7 inches. APF reported 6.73 inches of total rainfall, easily breaking the 72-year August 24-hour rainfall record of 3.84 inches (set in 1958) and the Aug. 4 daily rainfall record. At least one COCORAHS (Community Collaborative Rain Hail and Snow) Network observer, located near Gulfshore Boulevard just north of downtown Naples, reported 7.00 inches of rain (Fig. 7). The Royal Poinciana Golf Course rainfall network received more than 6 inches of rain across its entire course.

In north Naples, where heavy rainfall had fallen on several days during the previous week, rainfall totals were only in the three to five inch range. One observer in the Vineyards subdivision off Vanderbilt Beach Road and I-75 recorded 4.83 inches of rain during the day on Aug. 4, 2014.

By early on Aug. 5, 2014, the weather system had exited Florida and was trekking northeastward, parallel to the path of Tropical Storm Bertha. Early on Aug. 9, 2014, the remnants of Bertha (now an extra-tropical low) were merging with a middle-latitude storm over the northeast Atlantic and were enroute to an arrival on the west coast of Europe by early on Aug. 10 (Fig. 8).

© 2014 H. Michael Mogil

P.S. Note that Aug. 4, 2014 marked the first day of the 2014 Southwest Florida Middle School Weather Camp Program. Clearly, campers were treated to some really interesting weather.

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