The excessive heat warning covering the metropolitan area, including Johnson, Leavenworth and Wyandotte counties, has been extended until 9 p.m. Thursday.

The National Weather Service this morning said dangerous heat and humidity would continue across the region with afternoon temperatures approaching 100 degrees through Thursday.

An excessive heat warning is issued when there is a heat index of at least 105 degrees for more than three hours per day for two consecutive days, or a heat index of more than 115 degrees for any period of time.

An excessive heat warning means that a prolonged period of dangerously hot temperatures will occur. The combination of hot temperatures and high humidity will create a dangerous situation in which heat illnesses are likely. Prolonged exposure to heat and humidity of this magnitude, forecasters and health officials warn, can cause dehydration, heat exhaustion and heat stroke.

If you plan to be outside, health officials recommend:

• Avoid strenuous activity

• Drink plenty of water

• Wear lightweight, light-colored and loose-fitting clothing

• Wear sunscreen to avoid sunburn

Children, the elderly and those who are chronically ill are at the most risk in extreme heat.

The National Weather Service recommends that friends and family members regularly check on those at risk.

Temperatures inside cars also can become extreme within a matter of minutes, so officials advise against leaving children, the elderly or pets unattended in a vehicle.

Tuesday’s high is forecast to be about 99 degrees with an overnight low in the high 70s.