Environment Canada says the extreme heat baking much of the province in recent days will continue through tomorrow.
The heat warning remains in effect for Niagara and temperatures today and tomorrow are forecast to climb into the low to mid 30's.
Humidex values will also increase, reaching values near 40 on both days.
Overnight low temperatures are expected to be in the low 20's or in the high teens -- providing little or no relief from the heat.
A cool down is expected by Friday as a cold front passes through the province.
In St. Catharines the Out of the Heat emergency shelter will be offering respite from the heat and a little something to eat for those experiencing homelessness.
The community run shelter will officially open today at Grace Anglican Church at 238 Geneva Street.
The program will run six days a week (excluding Tuesdays) until August 31st.
Check in is at 8 p.m. and a light snack will be provided for those staying the night.
Participants will be provided with bedding and a cot and encouraged to attend the St. George Breakfast Program in the morning.