Subtropical storm Alberto, the first named Atlantic storm of 2018, has made landfall on Florida’s north-western coast.
Alberto passed the coast at Laguna Beach with maximum sustained winds of 45mph (72km/h), US meteorologists say.
Thousands of people were earlier evacuated from the Gulf of Mexico coast of Florida.
The storm is expected to weaken as it moves further inland. The hurricane season formally starts on 1 June.
Alberto is moving northwards at about 9mph, the National Hurricane Center says.
Many of the northern Florida panhandle’s beaches were empty of the crowds typical for Memorial Day – a holiday across the US to remember those who died serving in the country’s armed forces.
Alberto is forecast to drop as much as 30cm (12in) of rain across Mississippi to western Georgia and to bring storm swells of about 60-120cm (2-4ft) to low-lying areas.
Some tornadoes could also be touched off.
It is the first named storm of the season, with 21 other names still to be used, including Beryl, Ernesto, Kirk, Nadine and Rafael.
Last year, a number of deadly hurricanes hit the US and Caribbean.
Puerto Rico, for example, is still struggling with its recovery efforts following major infrastructure damage from Hurricane Maria in October.