Tampa and West Central Florida Slosh Through Two Weeks of Heavy Rain

It has been a very quiet tropical season in the Atlantic Basin. There have been only three named systems in the Atlantic so far this season (Ana, Bill, Claudette), and none of these tropical storms have directly affected Florida. Typically the west-central coast of Florida gets about 60 percent of its annual average rainfall in the months of June through September, coinciding with the first half of the tropical storm season.

Tampa flooding on August 2.
Credit: John Kassel via Facebook

In the past two weeks west-central Florida has received from 10 to 24 inches of rain resulting in persistent flooding and a general mess for residents. The Tampa Bay areas has been been the bulls-eye for the heavy rain, with Pasco, Pinellas, and Hillsborough Counties recording the highest rainfall totals.

14-day accumulated precipitation for Florida.
Source: NWS Advanced Hydrologic Prediction Service

The rain has resulted in persistent and widespread flooding. The flooding has closed numerous streets and roads, overloaded wastewater pumping stations, and forced the suspension of trash collection. In Pasco County the Anclote River threatened 5,700 homes with flooding, with more than 320 homes evacuated.

Flooding on August 4 in the Seven Springs area of Pasco County.
Credit: Pasco County Sheriff

The river crested at 25.25 feet at 11:45 a.m. EDT this morning and is expected to steadily fall to below flood stage on Friday. The record crest for the Anclote is 27.7 feet set on August 8, 1945. The last time the river was this high was in June 2012 when it reached a crest of 26.81 feet.

The reason for the rain was a frontal system which stalled over central Florida and a series of low pressure waves along that front. The cold front pushed into northern Florida on July 24. It stalled over central Florida on July 25, and that's when the skies opened up. Two to seven inches of rain fell on the Tampa Bay area in the 24 hour period ending on July 25, and it has rained every day since.

Surface map for 8:00 p.m. EDT July 25, 2015

The chart below plots the last 14 days of rainfall for CoCoRaHS Stations FL-HB-55 (Tampa 5.0 NNE),FL-PS-4 (Port Richey 2.0 NNE), and FL-PN-41 (Tarpon Springs 5.6 E), the highest totals for the period in Hillborough, Pasco, and Pinellas Counties respectively. Though the rainfall totals for the stations for the two-week period are similar, the three stations generally had wide day-to-day differences in rainfall. Note that there is no observation available for FL-PN-41 for August 4 as of this post, but other CoCoRaHS observers in the vicinity had another two to three inches of rain this morning.

Although July 25 marked the start of the very heavy rain, rain has fallen in this area every day since the middle of July. As of today FL-HB-55 has had 21 consecutive days of measurable rain, FL-PN-41 21 days, and FL-PS-4 23 days. The average July precipitation for this area is about 7.90" and the average August precipitation 8.80".  Average annual precipitation for this area is about 52 inches.

The 11.84 inches measured in July at the Tampa International Airport was the 8th highest July total since records began in 1939. The record is 20.59 inches in 1960.   However, it was on the low end of totals reported by CoCoRaHS observers in the areas. A few Hillsborough County stations reported more than 15 inches for July. However in Pasco County FL-PS-4 tallied 20.90 inches for July, and in Pinellas County FL-PN-41 measured 26.90 inches.

The Tampa Bay area got a break today, as most rain was north and east of the area as the low pressure system lifted northeast. It was located on the South Carolina coast today. More than four inches of rain was reported  along the South Carolina and North Carolina coasts this morning.

24-hour precipitation ending the morning of August 4.

  The low is expected to continue into the Atlantic before merging with another weather system, but not before more rain and winds affect the coastal areas.