This is a great table for calculating the Heat Index - the temperature the body feels when heat and humidity are combined.

http://www.nws.noaa.gov/om/heat/index.shtml

Today I ran an 8 miler in comparatively cool temperatures of 28C/82F, but when you combine it with the crazy 95% humidity this morning it certainly felt more like 34C/93F!

On days when it is 36C/97F and humidity is in the 70s my body sure knows about it as the Heat Index reaches 130F!