Your Florida Backyard NSiS Home Page Your Florida Backyard The Heat Index
The heat index (see chart below) is the "feels like", or apparent, temperature. As relative humidity increases, the air seems warmer than it actually is because the body is less able to cool itself via evaporation of perspiration.
As the heat index rises, so do health risks. When the heat index is 90°-105°F, heat exhaustion is possible. When it is above 105°F, it is probable. Heatstroke is possible when the heat index is above 105°F, and very likely when it is 130°F and above. Physical activity and prolonged exposure to the heat increase the risks.
*Heat exhaustion occurs when the body is dehydrated. *Heatstroke occurs when perspiration cannot occur and the body overheats. The following chart shows the health risks as temperature and relative humidity rise.

The Heat Index


Relative Humidity (percentage)
135° 120126 
130° 117122131 
125° 111116123131141 
120° 107111116123130139148 
115° 105107111115120127135143151 
110° 99102105108112117123130137143150 
105° 9597100102105109113118123129135142149 
100° 9193959799101104107110115120126132138144150 
95° 8788909193949698101104107110114119124130136140150 
90° 838485868788909193959698100102106109113117122126131
85° 787980818283848586878889909193959799102105108
80° 737475767777787979808181828384858687888990
75° 696970717272737374747575767677777878797980
70° 646465656666676768686969707070707171717172

   =Heatstroke risk extremely high       =Heat exhaustion possible
   =Heat exhaustion likely, heatstroke possible       =Fatigue possible
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