"Hurricane Joyce is also in the Atlantic so we need to see how those two systems are going to move around each other because that could have an impact".
Rainfall of 0.5 to 1.5 inches with isolated amounts to 3 inches are forecast across Puerto Rico and the southern United States Virgin Islands, with up to an inch anticipated across the remaining Windward and Leeward Islands.
"It's just extremely busy and it's even busier than previous year and all at once", Blake said.
"It's been an ordeal but we're coming through this fairly well", Arakawa said at a news conference.
"They're all interplaying with one another and it's not a particularly confident scenario", he said. But forecasters also said the opposite could happen when it brushed up against strong wind shear.
This general motion is expected to continue through the next few days. All lanes of Interstate 26 are westbound to allow more people to leave the coast and head inland toward the state capital of Columbia. Sustained winds slowed slightly to 125 miles per hour Tuesday afternoon, making it a Cat 3 storm.
The storm is projected to shift northeast with an increase in forward speed in the coming days, forecasters said.
President Donald Trump declared states of emergency for North and SC and Virginia, opening the way for federal aid.
A spokeswoman said: "Basically Helene is in the Atlantic at the moment and is crossing the Atlantic and is expected to track towards the UK".
"Wave heights to 83 ft were measured early this morning under the [northeast] quadrant of Hurricane Florence", tweeted the National Hurricane Center.
At 4:00 p.m., the centre of Isaac was located 667 miles east of the Lesser Antilles. Storm winds could intensify through the day and tonight, but weaken slightly Thursday as it nears the coast. It should dissipate by early next week, the hurricane center said. "Prepare for long power outages".
September 14 (UPI) Tropical Storm Helene was expected to bring heavy rain and wind to the Azores this weekend, the National Hurricane Center said Friday.