Heavy rainfall and isolated thunderstorms are expected to hit pockets throughout the GTA Saturday, which can bring about flash floods, water pools on roads and localized flooding in low-lying areas, Environment Canada warns. The federal weather agency says 50 to 75 millimetres of rain is possible in areas as far west as Guelph to east beyond Kingston. Heavy showers have already begun and are expected to continue on and off throughout the day, with a forecasted end this evening.