The Met Office has issued a yellow status severe weather warning for Derry.
Heavy rain and thunder storms are forecast.
The warning, which also applies to counties Antrim, Tyrone, Armagh and Down, was issued on Tuesday morning and is valid from 1pm right through to 10pm on Tuesday evening.
"Showers or rain is expected to develop through today," said the Met Office's Chief Forecaster.
"These becoming potentially heavy, prolonged and thundery by this afternoon. Locally torrential downpours are possible with 10 to 20 mm falling locally in an hour and as much as 30 to 40 mm in several hours. The thundery rain will clear from the west through the first half of the night."
For more information visit the Met Office website.