A significant low pressure system is threatening heavy rain and localized flooding in southern Ontario during the long weekend.
Environment Canada has issued a special weather statement for the Niagara Region.
Forecasters say periods of rain will spread across the region this afternoon.
The rain will become heavy at times and continue into Monday night, with things starting to ease off early Tuesday.
Total rainfall amounts averaging 30 to 60 mm are expected, but with locally higher amounts possible in thunderstorms.
Hamilton is already under a heavy rainfall warning as some localized flooding is expected with this storm system.