In an August, 2019 briefing on the approaching Hurricane Dorian, Trump claimed that Alabama would be affected:

And, I will say, the states — and it may get a little piece of a great place: It’s called Alabama.  And Alabama could even be in for at least some very strong winds and something more than that, it could be.  This just came up, unfortunately.  It’s the size of — the storm that we’re talking about.  So, for Alabama, just please be careful also.

The National Weather Service tweeted that this was in fact not the case. While 5 states declared national emergencies in advance of the hurricane, Alabama was not among them.

After multiple days of tweeting about how he was right, Trump displayed a hurricane map that appeared to be altered by Sharpie to extend the path into Alabama. It quickly became termed “Sharpiegate.”

When questioned about this, Trump claimed he knew nothing about it.

Two days later, the National Oceanic and Atmospheric Administration (NOAA), an agency within the Department of Commerce, issued an unsigned statement siding with Trump’s claims about Alabama. Shortly after, the New York Times reported that US commerce secretary, Wilbur Ross, had threatened the head of the NOAA with firings unless they publicly supported Trump’s claims.

In June, 2020, the Department of Commerce’s inspector general released a report on the issue. It confirmed that “the Department and NOAA issued the Statement in response to a request by the White House then-acting Chief of Staff, Mick Mulvaney, to Secretary of Commerce Wilbur Ross.”

The inspector general’s report further concluded that “the Statement undercut the NWS’s forecasts and potentially undercut public trust in NOAA’s and the NWS’s science and the apolitical nature of that science.”

A separate report by the National Academy of Public Administration found that NOAA’s scientific integrity had been compromised “intentionally, knowingly, or in reckless disregard.”

Trump also previously suggested stopping hurricanes with nuclear weapons.

Whitehouse.gov – Remarks by President Trump in Briefing on Hurricane Dorian
The New York Times – Trump Insists He Was Right About Hurricane Dorian Heading for Alabama
The Atlantic – Trump’s Most Pointless Lie
The Washington Post – Investigation rebukes Commerce Department for siding with Trump over forecasters during Hurricane Dorian
The Washington Post – NOAA leaders violated agency’s scientific integrity policy, Hurricane Dorian ‘Sharpiegate’ investigation finds
National Oceanic and Atmospheric Administration – Statement from NOAA, September 6, 2019
U.S. Department of Commerce, Office of Inspector General – Evaluation of NOAA’s September 6, 2019, Statement About Hurricane Dorian Forecasts
A Report by a Panel of the National Academy of Public Administration – An Independent Assessment of Allegations of Scientific Misconduct
Wikipedia – Hurricane Dorian–Alabama controversy