A tropical depression moving into the Gulf of Mexico is growing better organized, forecasters said Saturday, and is likely to bring drenching rain and coastal flooding to much of Florida’s Gulf Coast.

The storm strengthened into a tropical depression late Friday and is expected to become a tropical storm by Saturday night, once it has maximum sustained winds of 39 mph or more. If the depression reaches tropical storm status, it would be named Debby, the fourth named storm of the Atlantic hurricane season. 

Circulation was centered about 15 miles west of Havana on Saturday afternoon, but associated wind and thunderstorms were spread out over a broad region, including southern and central Florida, the Florida Keys and the Bahamas. The National Hurricane Center issued an alert on Saturday stating the depression started to move into the southeastern Gulf of Mexico and a tropical storm warning was issued for portions of the Florida Keys. 

Depression strengthens as the system nears Florida

The National Hurricane Center in Miami forecasts that the depression will strengthen as it curves northward off the southwest Florida coast, where the water has been extremely warm, with temperatures approaching 92 degrees Fahrenheit this week. On Saturday the moisture associated with this wave is expected to produce rounds of heavy rain and flooding. 

Predictions show the system could come ashore as a strong tropical storm or hurricane on Monday and cross over northern Florida into the Atlantic Ocean, where it’s likely to remain a tropical storm threatening Georgia and the Carolinas early next week. Tropical storm warnings are posted for most of Florida’s West Coast and the Dry Tortugas. A hurricane watch has been issued for Florida’s Big Bend between Indian Pass and Yankeetown.

A hurricane watch is posted for parts of the Big Bend and Florida Panhandle, recognizing that there is a chance that Debby could reach hurricane status before coming ashore.

A warning means storm conditions are expected within 36 hours, while a watch means that storm effects are possible within 48 hours.

Flash flooding and potential storm surge

Tropical storms and hurricanes can trigger river flooding and overwhelm drainage systems and the region’s canals. Forecasters are warning of 5 to 10 inches of rain, which could create “locally considerable” flash and urban flooding. Forecasters are already warning of moderate flooding for some rivers along Florida’s West Coast.

Some of the heaviest rains could actually come next week in a region along the Atlantic Coast from Jacksonville, Florida, north through coastal regions of Georgia, South Carolina and North Carolina. The storm is expected to slow down after making landfall.

“We could see a stall or a meandering motion around coastal portions of the southeastern United States,” National Hurricane Center Director Michael Brennan said in a Saturday briefing. “So that’s going to exacerbate not just the rainfall risk, but also the potential for storm surge and some strong winds.”

Flat Florida is prone to flooding even on sunny days when so-called king tides surge in coastal areas, and the storm is predicted to push up storm tides of 2 to 4 feet along most of Florida’s Gulf Coast, including Tampa Bay, with a higher tide of 3 to 5 feet predicted farther north in Florida’s sparsely populated Big Bend region.

Forecasters issued a storm surge warning on Saturday, saying there’s “a danger of life-threatening storm surge inundation” in a region that includes Hernando Beach, Crystal River, Steinhatchee and Cedar Key. Citrus County officials ordered a mandatory evacuation of coastal areas.