Met Éireann said: "Current indications are that (ex-) tropical storm Helene will approach Ireland's south coast during Tuesday".
As Graham says, "just because you have a landfall to your south doesn't mean you're out of the woods, because the winds are huge around this system". "Heavy and long-lasting rainfall could lead to catastrophic flooding in inland parts of North Carolina, South Carolina and Virginia".
Sustained winds remained at 90 miles per hour, but the storm - which was never expected to threaten the USA coast - should begin to weaken over the next day and become a tropical storm on Thursday, forecasters said in an 11 a.m. advisory.
"Florence is forecast to be an extremely risky major hurricane as it approaches the USA coast", the NHC said.
According to the Accumulated Cyclone Energy, or ACE, a metric that combines the duration and intensity of storms, the Northern Hemisphere has already reached 159 percent of its average for this point in the year.
There is a small chance that injuries could occur from large waves and beach material being thrown onto sea fronts.
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"We can not stress this enough, Florence poses a very serious threat to people who live far away from the coast", said a National Weather Service tweet late Tuesday.
Winds of 40 mph extend outward up to 115 miles (185 km) from the center of the tropical cyclone. Strengthening is forecast through Wednesday.
Isaac was a hurricane Sunday night but downgraded when maximum sustained winds fell below 74 miles per hour.
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Storm Helene is heading towards the UK from the Atlantic and is separate from Hurricaine Florence, which is starting to hit the eastern United States.
The National Hurricane Center (N.H.C.) in its 5:00 p.m. advisory said all tropical storm watches and warnings for Isaac have been discontinued, news that will be welcomed by interests in the Caribbean.
The implications of a major landfalling hurricane are devastating. The storm is expected to slow down and possibly stall near or over the coast on Friday.