Calculate NOAA "feels like" apparent temperature from ambient temperature and relative humidity with heat exhaustion and heat stroke danger warnings.
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The Heat Index Calculator calculates the apparent "feels like" temperature using the official NOAA National Weather Service Rothfusz regression equation. It combines dry-bulb air temperature with relative humidity to evaluate the human body’s ability to cool itself through sweat evaporation.
HI = -42.379 + 2.049T + 10.143RH - 0.2248T\cdot RH - 0.006838T^2 - 0.05482RH^2 + 0.001229T^2 RH + 0.0008528T RH^2 - 1.99\times 10^{-6}T^2 RH^2Where T is ambient air temperature in °F and RH is relative humidity in percent. High humidity impedes sweat evaporation, drastically raising thermal body stress.
Scenario: Ambient temperature of 92°F with 65% relative humidity
Temperature T = 92°F, Relative Humidity RH = 65%.
Apply Rothfusz polynomial regression with humidity boundary adjustments.
Heat index output: 108.3°F (42.4°C).
Risk category: Danger (104°F to 124°F).
The human body cools itself primarily through perspiration. When the air is saturated with moisture, sweat cannot evaporate efficiently into the air, trapping body heat inside.
1. Caution (80°F–90°F): Fatigue possible. 2. Extreme Caution (91°F–103°F): Heat cramps and exhaustion possible. 3. Danger (104°F–124°F): Heat cramps and exhaustion likely; heat stroke possible. 4. Extreme Danger (≥125°F): Heat stroke imminent.
The official NOAA Heat Index is calculated for shady, light wind conditions. Exposure to full direct sunlight can increase heat index values by up to 15°F (8°C).
Heat index measures how hot human skin feels in shaded conditions. Wet-bulb temperature (WBT) measures the lowest temperature achievable by evaporative cooling; a sustained wet-bulb temperature of 95°F (35°C) is the absolute survivability threshold for humans.
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Heat cramps and heat exhaustion likely. Heat stroke possible with prolonged activity.