Forecasters predict that Tropical Storm Idalia will grow into a devastating Category 3 hurricane, threatening Florida and Cuba.
Idalia is anticipated to strengthen before reaching landfall near Big Bend, Florida, on Wednesday, according to the National Hurricane Center (NHC).
Another storm, Franklin, could bring deadly storm surges to the United States’ East Coast and Bermuda.
It comes as the Atlantic hurricane season approaches its climax.
Franklin is the first major hurricane of the season, which runs from June to November. It is currently a Category 4 storm, packing 145mph (230km/h) winds, but is expected to weaken by midday Tuesday, said the NHC.
In an update on Monday afternoon, the agency said Franklin was already causing life-threatening surf and rip currents along the south-eastern coast of the US.
For now, Florida is focused on Idalia, with Governor Ron DeSantis warning the state should brace for “major impacts” from that storm.
“This is going to be a powerful hurricane,” he said at a news conference on Monday.
“This is absolutely going to impact the state of Florida in many, many ways.”
President Joe Biden has authorized a state of emergency proclamation in anticipation for the storm.
The NHC reported at 20:00 EDT on Monday ((01:00 GMT) Tuesday) that Idalia is moving north at 8mph with maximum sustained winds of 70mph.
When a storm’s maximum sustained winds hit 74 mph or more, it is classified as a hurricane.
According to the National Hurricane Center, Idalia may bring “life-threatening” storm surges and “hurricane force winds and scattered flash and urban flooding” to areas of Florida’s west coast and the Florida Panhandle as early as Tuesday.
The storm is anticipated to dump 4-7in (10-18cm) of rain on western Cuba and bring severe storm surges. A hurricane warning is in force for the Cuban city of Pinar del Rio.
Idalia was 20 miles (30km) west of Cuba on Monday evening. It has forced thousands of Cubans to evacuate towns on the island’s west coast.
Storm surges of up to 11ft (3.3m) are forecast for some north-western Florida towns.
“The deepest water will occur along the immediate coast in areas of onshore winds, where the surge will be accompanied by large and dangerous waves,” the NHC said.
Tampa International Airport will be closed from midnight on Monday in preparation for the storm.
Florida’s governor has declared a state of emergency in 46 counties, across the northern half of the state.
Mr DeSantis said several counties on the Gulf Coast would be forced to evacuate because of Idalia, while schools would also close.
He encouraged Florida residents in low-lying coastal areas to seek higher ground.
“Floridians, you need to be executing your plans now,” he said.
The governor said more than 1,100 National Guardsmen had been mobilized with 2,400 high-water vehicles and other rescue equipment.
Officials have prepared 400,000 gallons of fuel to be deployed at petrol stations along evacuation routes, Mr DeSantis said.
State officials also warned that as the storm approached, many homes in the area might lose electricity.
Forecasters predict that heavy rain will fall in Georgia, North Carolina, and South Carolina.
Idalia is a tropical storm that made landfall on Florida’s west coast less than a year ago, killing over 100 people.
The influence of climate change on tropical storm frequency is yet unknown, although rising sea surface temperatures warm the air above, making more energy available to hurricanes. As a result, they will most likely be more severe with more significant rainfall.