Tampa Bay residents may have found themselves missing the summer showers this year.

Recent rainfall data shows that Southwest Florida, including the Tampa Bay area, experienced the driest rainy season in 26 years. As a result, Tampa Bay Water, the regional utility, issued a water shortage warning Oct. 2 and urged residents to conserve water.

The region’s official end to the four-month rainy season falls on Sept. 30 every year, according to the Southwest Florida Water Management District, commonly known as Swiftmud. And while the district has yet to crunch the official numbers, water managers say early estimates show this season was the driest since 1996.

The district as a whole and its southern and central counties, which include the Tampa Bay area, saw below-normal rainfall accumulations, Susanna Martinez Tarokh, spokesperson for the district, said in an email to the Tampa Bay Times. However, rainfall this summer was normal in the region’s northern counties.

This year is also shaking out to be one of the driest to date, according to the National Weather Service’s Tampa Bay office. In St. Petersburg, the current rainfall total is the fourth-lowest in more than 100 years. Tampa’s rainfall so far this year ranks as the seventh-driest since 1890.

The Tampa Bay area soaked up 35.6 inches of rain from Jan. 1 to Oct. 1, according to Swiftmud. The area typically sees an average of 45.2 inches of rainfall during that time period.

A late start to prolonged rainfall patterns also made it Southwest Florida’s shortest rainy season in more than a decade.

A shorter rainy season typically signals a drier one, according to Jayasankar C B, a researcher with the Center for Ocean-Atmospheric Prediction Studies at Florida State University. He found this past September’s rainfall strayed furthest from previous years — Southwest Florida received less than half of the rain expected last month compared to the 22-year average. September rains typically bring about 9 inches, but last month saw just shy of 3.7 inches of rainfall.

“The seasonal cycle of rainfall in Florida is not as regular as it sounds,” he said.

Jayasankar collects daily rainfall data and sends his findings to water management districts around Florida. He said he warned water managers in June about the late start to the rainy season in Southwest Florida.

His dataset goes back to 2001 and draws from a cluster of satellites operated by NASA and the National Oceanic and Atmospheric Administration.

“There aren’t any other reliable seasonal estimates in this rapidly growing state, so water resource managers welcome the outlook,” he said.

Current climate models don’t offer reliable seasonal predictions in the summer, Jayasankar said. In May, the National Oceanic and Atmospheric Administration predicted above-average rainfall in Florida during this rainy season. But drought conditions at the start of the year prevailed through September in the Tampa Bay area and the rest of Southwest Florida.

When rainfall predictions don’t match the season’s actual rainfall amount, utilities and water management districts can have a hard time filling reserves and meeting water demands, Jayasankar said.

Enter water shortages.

Lessons learned in “water wars”

About 25 years ago, overpumping at Pasco County wellfields lowered lake levels and dried out wetlands, culminating in Tampa Bay’s “water wars.” This led to the formation of Tampa Bay Water in 1998.

Jayasankar said a major drought in the summers of 1999, 2000 and 2001 led to increased interest in diversifying water sources. Some water utilities in Florida were forced to seek alternative sources of fresh water or expand their water storage.

After the drought, Tampa Bay’s surface water treatment plant opened in 2002, expanding water supplies by drawing from the Hillsborough and Alafia rivers.

Water shortages are fairly common in Southwest Florida, though more frequent during the state’s dry winter and spring months. The last shortage warning occurred in May 2020, when the Tampa Bay area experienced just 18% of expected rainfall for April.

A Stage 1 water shortage warning — like the one issued earlier this month — goes into effect when the rainfall deficit exceeds 5 inches. In Tampa this year, rainfall totals have fallen more than 14 inches below normal since January, according to the National Weather Service’s Tampa Bay office.

Because Tampa Bay Water looks at rainfall over the last 12 months, it calculated the deficit to be lower: 8.3 inches, which triggered the current warning. This window spans from September 2022 to this past September, and also included the deluges brought by Hurricane Idalia and Hurricane Ian last year, said Warren Hogg, the utility’s chief science officer.

In addition to the drought conditions for much of the year, outdoor watering also is partly to blame for the current water shortage, utility spokesperson Brandon Moore said in an Oct. 2 news release.

The regional utility says it has enough drinking water to meet demand, but it is asking residents to conserve their outdoor water use through the dry season, which spans from October to May. To make up the difference, the utility says it is drawing on its varied water sources.

Tampa Bay Water’s C.W. Bill Young Regional Reservoir, the regional utility’s water storage facility, is nearly full at 14 billion gallons of its 15.5-billion-gallon capacity, according to the release. And the seawater desalination plant should help to replenish water supplies beginning in November, according to Moore.

Why was it so dry?

Rodney Wynn, a meteorologist with the National Weather Service’s Tampa Bay office, said wind patterns are to blame for this summer’s diminished rainfall.

A westerly flow dominated July and August, which pushed most showers and storms away from the coast.

“So any showers and storms that did develop,” Wynn said, “they didn’t last very long over the west coast of Florida. They moved eastward.”

But he said we could make up for lost rainfall during the colder months. Scientists with the National Oceanic and Atmospheric Administration predict this year’s El Niño will persist through the winter, which Wynn said could bring showers.

It could also mean higher chances of severe weather throughout the winter.

“Because with El Niño, we’ll get more areas of low pressure and cold fronts that move farther southward,” he said. “So that’ll bring us our higher rain chances.”

Contact Jack Prator at jprator@tampabay.com.