Tropical Moisture to Fuel Soaking Storms in Florida as the State's Wet Season Arrives

Linda Lam
Published: May 13, 2018

Florida's wet season is about to begin with some much-needed rainfall for central and southern portions of the state, good news for areas where drought conditions have recently developed.

(MORE: What to Watch Out For and Look Forward to in May)

The instigator for the soggy weather pattern is an upper-level area of low pressure that has developed in the eastern Gulf of Mexico. This low will bring an influx of tropical moisture across Florida and other parts of the Southeast early this week, leading to numerous showers and thunderstorms.

Water Vapor Satellite

This weather system will also be accompanied by a weak surface low developing in the Gulf of Mexico. When low-pressure systems like this one develop over water this time of year, we always watch them closely for possible development.

Right now, the odds are very low that this system will develop into a tropical or subtropical depression or storm, but even if development did occur, heavy rainfall would remain the primary concern.

Current Radar, Watches and Warnings

Much of southern and central Florida can expect at least 1 to 3 inches of rainfall through midweek. Locally higher amounts are expected in heavier thunderstorms and totals of 3-7 inches are likely in southeastern and eastern Florida through midweek.

The moisture will also fuel downpours that result in rainfall totals of 1 to 3 inches across other parts of the Southeast this week.

(MORE: We're Entering the Prime Time for Flash Flooding)

Rainfall Forecast

Although this rain is beneficial overall, there could be pockets of localized flooding in the week ahead.

The good news: higher rainfall amounts look likeliest in areas where it is most needed in the Sunshine State.

As of May 8, more than 26 percent of the state was in moderate drought, with a portion of South Florida in severe drought, according to the U.S. Drought Monitor.

Drought conditions as of May 8, 2018.
(U.S. Drought Monitor)

Additionally, just over half of the state was at least abnormally dry. Drought conditions did not begin to develop there until late February.

Miami only measured 0.37 inches of rainfall in February, 1.88 inches below average for the month. This dry trend was exacerbated in March, when Miami only picked up 0.19 inches, compared to the average rainfall for March – 3 inches. Similar experiences were observed all across South Florida.

This dry pattern began to shift in late April in the area, but locations such as Fort Lauderdale and Naples remained more than 6 inches below average year-to-date as of Friday. But there appears to be hope for a wetter pattern as the wet season commences.

Wet Season Begins This Month in Parts of Florida

The May-to-October time period when most of the annual precipitation occurs in Florida is known as the wet season.

For example, Miami receives about 45 inches of rain – almost 75 percent of its average annual rainfall – from May to October. By late May, the rainy season is usually ramping up across South Florida. 

Farther north, Tampa records about 70 percent of its average annual rainfall of 46.3 inches during the wet season. The beginning of the rainy season is a bit later, usually in mid-June, across central and northern Florida. 

The purple dashed lines depict typical sea-breeze boundaries that help to trigger storm formation from late spring into early fall.

The reason for the increase in rainfall is that cold fronts do not track into Florida during this time, which allows for warmer temperatures and humid conditions to dominate.

(MORE: Rip Currents Have Been More Deadly Than Tornadoes and Lightning This Year)

As humidity increases, thunderstorm activity increases. Thunderstorms develop along sea-breeze fronts as cooler air slides inland from the Gulf of Mexico and the Atlantic Ocean, as shown above.

In addition, hurricane season officially runs from June 1 through Nov. 30 and brings an increased chance for rainfall. It's important to remember that a strong hurricane is not needed to bring excessive rainfall; slow-moving tropical storms or even tropical depressions can result in heavy rainfall and flooding in the region.

Although the beginning of the wet season is good news regarding the needed rainfall, one problem this brings is the possibility of dry lightning. This occurs when lightning strikes hit the ground outside of rainfall, and these strikes can create grass fires, especially where the ground is dry following the dry season. 

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.