Tropical Storm Bertha lashes South Carolina in sunrise surprise that could affect NASA SpaceX launch

"Life-threatening" flash flooding is expected across parts of Virginia, and South and North Carolina, after Tropical Storm Bertha made landfall sooner than expected.

NASA satellites are closely watching the storm as it prepares to send two astronauts to space in a historic launch aboard SpaceX on Wednesday afternoon.

The National Weather Service, meanwhile, warned that the second named storm of the season would cause ongoing river flooding across the region.

The tropical storm was named about 8 am on Wednesday and hit the coast near Charleston less than two hours later, with the state's Department of Natural Resources calling it "a sunrise surprise".

Downed trees and less than 1,000 power outages were reported as several streets flooded in Charleston with high brown water mixing with trash, according to reports from the Associated Press.

The National Hurricane Centre issued an advisory two warning with reports of maximum sustained winds of 50 miles per hour.

While the strength of the storm is expected to weaken throughout the day, more than six million people are under flash flood watches in Charleston, Charlotte and Roanoke with two to four inches of rainfall expected.

Tropical Storm Bertha may affect the SpaceX launch at Kennedy Space Centre in Florida. The 45th Weather Squadron, whose mission it is to exploit the weather to assure safe access to air and space, has been tracking the storm.

"The primary concerns for launch are flight through precipitation, as well as the anvil and cumulus cloud rules associated with the afternoon convection," the squadron wrote in its official launch mission forecast.

It predicted a 50 per cent chance of bad weather at the time of the launch, targeted for 4.33pm eastern time.

Donald Trump left the White House to travel to Florida, where he will watch the NASA launch.

Bob Behnken and Doug Hurley will be hitching a ride aboard Elon Musk's SpaceX Crew Dragon rocket to the International Space Station. It would be the first launch of US astronauts from US soil in almost a decade.

"Teams are closely monitoring launch and downrange weather," SpaceX said in a tweet.

Bertha is the second named storm of the season after Tropical Storm Arthur hit North Carolina earlier in May, making 2020 the sixth consecutive year a named storm has developed before the official start of the Atlantic hurricane season on 1 June.