Even though summer doesn't officially start until next week, it will feel like summer and then some this weekend.

The National Weather Service has issued a Heat Advisory for northeast Missouri and western Illinois from noon Friday through 8 p.m. Monday.

Officially, counties affected are Audrain, Knox, Lewis, Lincoln, Marion, Monroe, Pike, Ralls and Shelby in Missouri, and Adams, Brown and Pike counties in Illinois.

Forecasters say a dangerous combination of heat and humidity will begin in the area Friday afternoon and will continue at least through early Monday evening, with little relief from the heat and humidity at night.

High temperatures in the 90s and dewpoints in the low 70s will result in heat index values up to 103 degrees.

The weather services warns that the combination of hot temperatures and high humidity will lead to an increased risk of heat-related stress and illness. The very young, the elderly, those without air conditioning, and those taking part in strenuous outdoor activities will be at the most risk. Also, car interiors can reach lethal temperatures in a matter of minutes.