In a news release the city says the Canadian Hurricane Centre is forecasting rapid changes in water levels along the Avalon Peninsula about two to three hours before high tide at around 10 a.m.
Officials say areas that should be particularly concerned include Quidi Vidi, Battery and Blackhead Village.
The hurricane centre says the heaviest rainfall will stay offshore Wednesday and into Thursday. The large storm barrelled past Bermuda on Tuesday.
Rafael reached hurricane strength late Monday south of Bermuda with top sustained winds of 140 km/h.
No serious damage was reported as the storm brushed by the island on Tuesday. According to officials, Bermuda saw tropical storm strength winds and minor power outages, but the eye of the storm remained far away from land.
Now, Rafael continues to head northeast over the Atlantic and computer models suggest a track along the extreme southern edge of the Grand Banks.
"A trough of low pressure over Newfoundland will move eastward on Wednesday and track east of the island as Rafael approaches," says the Canadian Hurricane Centre. "Some tropical moisture from Rafael will likely feed into the trough, which would lead to some enhanced rainfall over the Avalon Peninsula."
Be sure to tune into The Weather Network on television for all the latest updates on post-tropical storm Rafael.