BOSTON • Subtropical Storm Alberto had a burst of strength as it closed on Florida's Panhandle, where it was set to go ashore yesterday, and was spreading heavy rain across the southern United States, potentially causing more than US$1 billion (S$1.3 billion) in economic losses.
Forecasters said Alberto could bring life-threatening high water to southern coastal states when it slams an area from Mississippi to western Georgia with up to 30cm of rain and possible tornadoes.
"Alberto has maximum sustained winds of 65mph(105kmh), which is about 10mph (16kmh) shy of being a hurricane. This is definitely a dangerous storm," said Mr David Roth, a meteorologist with the National Weather Service's Weather Prediction Centre.
After reaching the coast, the storm will bring powerful winds and heavy rain as it moves into the Tennessee Valley today and tomorrow, said the US National Hurricane Centre.
Heavy rain has already fallen in southern states, and flood and flash-flood watches span the region, reaching as far north as North Carolina and Tennessee, said the National Weather Service.
Governors in Florida, Mississippi and Alabama last Saturday declared states of emergency, and thousands of Florida residents evacuated homes on Sunday as the storm headed north through the Gulf of Mexico.
"The main concern from Alberto is flooding; not so much along the immediate coast, but inland, from the heavy rain that is coming on top of more than a week of rain across the south-east," said Mr Chuck Watson, a disaster modeller at Enki Research in Savannah, Georgia.
"A secondary concern is that even relatively minimal tropical storm winds can topple trees because of saturated soils and water-heavy limbs."
Speed of Alberto's maximum sustained winds, about 16kmh shy of being a hurricane.
Alberto could cause US$400 million to US$500 million of damage across the region, including to cars crushed by toppled trees, wrecked roofs and flooding, Mr Watson said in an interview.
On top of that, there could be as much as US$600 million in lost holiday spending as Alberto puts a damper on plans during the Memorial Day three-day weekend.
Last Friday, ExxonMobil pulled non-essential personnel from its Lena oil production platform and Royal Dutch Shell shut its Ram Powell hub, but most other energy companies are leaving offshore crews in place while they watch this year's first Atlantic storm.
Chevron Corp also shut oil production and evacuated personnel from its Blind Faith and Petronius platforms last Saturday.
Deadly hurricanes in the US and the Caribbean last year caused hundreds of billions of dollars in damage, massive power failures and devastation to hundreds of thousands of structures.
Alberto formed several days ahead of the official start of the six-month Atlantic hurricane season on June 1.
Storms in the gulf are closely watched because 5 per cent of US natural gas and 17 per cent of crude oil production come out of the region, according to the Energy Information Administration.
Onshore areas along the coast also account for about 45 per cent of US refining capacity and 51 per cent of gas processing.
A separate storm system on Sunday caused flash flooding in the Baltimore suburb of Ellicott City in Howard county, Maryland, turning its historic Main Street into a raging river with water reaching past the first floor of buildings and sweeping cars down the road.
Howard county authorities said a 39-year-old man was missing after he was swept away as he tried to help rescue people from floodwaters.
Maryland Governor Larry Hogan declared a state of emergency for the area being rebuilt after a devastating flood about two years ago that killed two people and damaged dozens of buildings.