The Met Office has upgraded a weather warning for Derry from yellow to amber.
The weather warning is for wind that could bring gusts as strong as 75mph inland.
The weather warning is valid from 8:00am to 5:00pm on Wednesday.
"Storm Ali will bring a spell of very strong winds to Northern Ireland from early on Wednesday morning," wrote the Met Office on their official website.
"Strong winds will be accompanied by heavy squally showers.
"Winds will ease from the west through the afternoon."