A deluge of rain from Tropical Storm Eta has caused flooding across southern Florida’s most densely populated urban areas, stranding cars, flooding businesses, and swamping entire neighbourhoods with fast-rising water.

The system made landfall in the Florida Keys and posed a serious threat across southern Florida, which was already drenched from more than 14in of rain last month.

After striking Nicaragua as a Category 4 hurricane and killing nearly 70 people from Mexico to Panama, the storm moved into the Gulf of Mexico early on Monday near where the Everglades meets the sea, with maximum sustained winds of 50mph.

Eta hit land late on Sunday as it blew over Lower Matecumbe, in the middle of the chain of small islands that form the Keys, but the heavily populated areas of Miami-Dade and Broward Counties bore the brunt of the storm.

It is the 28th named storm of a busy Atlantic hurricane season, tying the 2005 record. Hurricane season lasts until November 30.

By mid-afternoon on Monday, the storm was about 140 miles west-south-west of the Dry Tortugas, moving south west at 16mph. It was expected to slow down and strengthen overnight. Rain and wind were felt as far north as the Tampa Bay area.

Forecasters said the system could intensify again into a minimal hurricane as it slowly moves up the south-west Gulf Coast. It is just far enough offshore to maintain its strength while dumping vast amounts of water across the lower third of the Florida peninsula.

Fort Lauderdale mayor Dean Trantalis called it a 100-year rain event.

Tropical Storm Eta in the Gulf of Mexico
Tropical Storm Eta in the Gulf of Mexico (NOAA/AP)

“Once the ground becomes saturated, there’s really no place for the water to go,” he said. “It’s not like a major hurricane. It’s more of a rain event, and we’re just doing our best to ensure that the people in our community are being protected.”

City officials dispatched 24 tanker trucks with giant vacuums to soak up water from the past few weeks. The city also passed out 6,000 sandbags to worried residents over the weekend, but water seeped into homes and stranded cars.

In the Keys, the mayor ordered mandatory evacuations for mobile home parks, campgrounds and other low-lying areas.

School districts closed, saying the roads were already too flooded and the winds could be too gusty for buses to transport pupils, but the islands were spared any major damage, and officials expected shelters to close and schools to reopen by Tuesday.

Eta is not done yet with Cuba, 90 miles south of Florida, where the storm continued to swell rivers and flood coastal zones.

Some 25,000 people were evacuated with no reports of deaths, but rain continued, with total accumulations of up to 25in predicted. A tropical storm watch was in effect for parts of the island.

Authorities in Central America are still surveying the damage after days of torrential rain. Official death tolls totalled at least 68 people, but hundreds more are missing and many thousands are in shelters after flash floods tore through communities of improvised homes on unstable mountainsides.