US President Donald Trump answered "don't know" when asked why a weather map he showed to reporters in the Oval Office had apparently been altered to back up his claims about the path of Hurricane Dorian.

Key points: The revised forecast map included a half-circle that extended the cone of uncertainty over part of Alabama

The revised forecast map included a half-circle that extended the cone of uncertainty over part of Alabama On Sunday Mr Trump repeatedly said Alabama was under threat

On Sunday Mr Trump repeatedly said Alabama was under threat But meteorologists decided on Saturday that the state would not be hit

Mr Trump has been under fire in recent days for repeatedly claiming on Sunday that parts of Alabama could be hit by the giant storm, which has devastated the Bahamas.

His claims had forced the state's weather bureau to tweet: "Alabama will NOT see any impacts from #Dorian."

"We repeat, no impacts from Hurricane #Dorian will be felt across Alabama. The system will remain too far east," the meteorologists said.

The map the President showed to reporters on Wednesday was the same as one produced by the National Oceanic and Atmospheric Administration last week — but it included what appeared to be a hand-drawn half-circle that extended the cone of uncertainty over areas of Alabama.

Unveiling the graphic, Mr Trump told reporters that Alabama was in the original hurricane forecast.

The revised map (left) and the original from the National Oceanic and Atmospheric Administration (right) ( Reuters/NOAA )

"Actually, we have a better map than that which is going to be presented, where we had many lines going directly — many models, each line being a model — and they were going directly through," he said.

"And in all cases Alabama was hit if not lightly, in some cases pretty hard."

When asked about discrepancies with the original map, Mr Trump said: "I don't know. I don't know."

The Washington Post later reported that a White House deputy press secretary had confirmed the drawing was made using a black marker pen.

Hours later Mr Trump tweeted another map, dated August 28, that showed Alabama in the hurricane's path.

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The image, credited to a local agency called the South Florida Water Management District, includes text at the bottom saying: "NHC Advisories and County Emergency Management Statements supersede this product. This graphic should complement, not replace, NHC discussions."

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Although earlier forecasts had shown parts of Alabama on the edge of the five-day cone of uncertainty, by Saturday meteorologists had been adamant that the state was in the clear, despite the President's assertions.

Asked if Mr Trump had been briefed about the potential impact to Alabama, Christopher Vaccaro, a spokesman for the National Oceanic and Atmospheric Administration, wrote in an email: "The current forecast path of Dorian does not include Alabama."

The National Hurricane Centre said it expected Dorian to bring life-threatening storm surges and flooding to large parts of the US east coast in the coming days.

On Wednesday afternoon (local time) the category two hurricane was about 210 kilometres south of Charleston, South Carolina, with sustained top wind speeds of 175 kilometres per hour. It was moving to the north-northwest at 13 kph.

ABC/wires