From the Spaceflight Meteorology Group:
The National Weather Service has issued a Heat Advisory through 9PM today that includes JSC.
Clouds kept the maximum temperature down yesterday to 91 degrees but the combination of warm temperatures and high humidity sent the maximum heat index reading to 104. So far the minimum temperature at JSC Building 30 this morning has only been 83 degrees which would set a daily record for warmest minimum temperature. The heat index should rise above 100 by 10:30 AM with max values of 106 to 108 between 2:30 and 5:00 this afternoon. Slightly higher heat index readings can be expected at NASA Ellington Field and Sonny Carter Training Facility.
The NWS issues a Heat Advisory when the heat index >= 108 or the temperature >= 103 F. Please take extra precautions if you work or spend time outside.