That development came as congressional Democrats demanded answers about how and why NOAA issued a statement backing Trump.
The White House official said Mulvaney did not direct Ross to threaten any firings or make any other threats over the incident but expressed a view that the forecasters had overstepped in their contradiction of the president, maintaining that Trump was accurate to say that Alabama could be affected by the storm.
The New York Times was the first to report of the White House’s direct involvement in the administration’s effort to pressure NOAA to publicly repudiate the forecasters who tweeted definitively that “Alabama will NOT see any impacts from #Dorian.”
President Trump on Wednesday denied any personal involvement in coercing the federal scientific agency to take corrective action.
"No, I never did that," Trump told reporters in the Oval Office. "That was a whole hoax about the hurricane when they talked about Alabama. It was fake news from the beginning. It was a fake story."
Commerce Department officials have described the story as "false.” The department’s inspector general has said the matters are now “under review.”
A separate Commerce Department spokesman said “Secretary Ross did not threaten to fire any NOAA staff over forecasting and public statements about Hurricane Dorian."
Last week President Trump also denied knowing anything about how that weather map appeared altered with a black marker to show Alabama in Dorian's path.
But multiple sources in the White House have since confirmed to ABC News that it was Trump himself who drew on the map.
Members of Congress were briefed Tuesday on the reported threat to fire NOAA staff, according to people familiar with the ongoing conversations.
On Wednesday, Senate Democrats sent a letter to the Commerce inspector general demanding answers.
“Scientists within the federal government work for the American people, not for private industry or the President’s personal vanity. Individuals and families across the country rely on weather forecasting to determine everything from what they wear each day to the decision to evacuate a home during extreme weather events. As deadly extreme weather becomes more and more common, maintaining public trust in these reports becomes increasingly important. Agency officials should not be sacrificing trustworthy weather reporting for political gain,” the senators wrote in the letter.
Democratic Sen. Mazie Hirono of Hawaii blasted the Trump administration for allegedly retaliating against NOAA employees.
“I am extremely concerned with anytime that there is a threat to fire people, to discipline people for stating facts, that should be a concern to all of us,” Hirono told ABC News. “But sadly that's par for the course for this administration because they do not rely on facts or science for their positions. They have a position and everybody else has to conform to that position.”
She added: “That's very dangerous for our country, but it's been going on pretty much since the president has taken office because he lies every single day and he just wants people around him who will enable him to keep on lying to the American people.”
ABC News' Matthew Vann, Katherine Faulders and John Santucci contributed to this report.