A severe thunderstorm watch is in effect for a large portion of New Brunswick.
Environment Canada says the alert stretches from St. Stephen all the way up through Campbellton.
There could be strong winds, up to 1 to 2 cm of large hail, and lots of rain with 30 mm in the heaviest downpours.
The forecaster says there is also a slight risk of a tornado.
The alert will be in effect until later Friday evening.
Parts of Northeastern Nova Scotia and Cape Breton are under a severe thunderstorm watch as muggy conditions continue developing across the region.
Environment Canada says these storms could be capable of producing heavy rain with local amounts of up to 40 millimetres per hour.
Storms are expected to start Wednesday afternoon and continue into the early evening.
This follows a major flash flood last Sunday that damaged more than 100 homes in Eskasoni First Nation.
Weather experts say when thunder roars, you should head indoors.
Environment Canada has issued a severe thunderstorm warning for parts of Annapolis County as a line of storms moves north through southwestern Nova Scotia.
Meteorologists say the thunderstorms, currently near Kejimkujik National Park, are producing intense rainfall rates of up to 25 millimetres per hour. The storms are expected to continue tracking northward through the region.
The heavy downpours could lead to localized flash flooding and significantly reduced visibility for drivers. Residents are being urged to use caution if travelling and to watch for rapidly changing weather conditions.
Environment Canada advises people to seek shelter immediately if threatening weather approaches and to continue monitoring forecasts and warnings for updates.