Manitoba is in the grips of a heat warning.

It began Thursday in the western part of the province but now blankets nearly the entire southern half.

Temperatures in most places under the warning — which stretches as far north as Grand Rapids and as far south as the U.S. border — are expected to climb between 31 C and 34 C but the humidity will make it feel closer to 40, according to Environment Canada.

CBC meteorologist John Sauder's forecast for Winnipeg calls for 33 C on Friday and 32 C on Saturday.

The hot and humid conditions will step aside Saturday evening as a cooler air mass passes through, bringing more seasonal daytime highs around 26 C and 27 C for Sunday and Monday.

The heat also brings some instability in the weather, which means the potential for thunderstorms.

Environment Canada has issued severe thunderstorm warnings and watches for a number of places in the province, including the Interlake region, Dauphin, Russell, Gladstone, McCreary, Selkirk, and Gimli.

People are urged to watch for the effects of heat illness: swelling, rash, cramps, fainting, heat exhaustion, heat stroke and the worsening of some existing health conditions.

Stay cool, drink lots of water and never leave people or pets inside a parked vehicle, where the temperature increases exponentially.

Symptoms of heat illness include dizziness/fainting, nausea/vomiting, rapid breathing and heartbeat, extreme thirst and decreased urination with unusually dark urine.

More information on how heat affects the body and how to protect yourself can be found on the Manitoba government website.