NOAA Heat Index Calculator

NOAA Heat Index Formula:

\[ HI = -42.379 + 2.049T + 10.143RH - 0.225T RH - 6.838 \times 10^{-3}T^2 - 5.482 \times 10^{-2}RH^2 + 1.229 \times 10^{-3}T^2 RH + 8.528 \times 10^{-4}T RH^2 - 1.99 \times 10^{-6}T^2 RH^2 \]

Heat Index:

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1. What is the NOAA Heat Index?

Definition: The Heat Index (HI) is a measure of how hot it feels when relative humidity is factored with the actual air temperature.

Purpose: It helps assess the risk of heat-related illnesses by indicating the perceived temperature under different humidity conditions.

2. How Does the Calculator Work?

The calculator uses the NOAA's complex regression equation:

\[ HI = -42.379 + 2.049T + 10.143RH - 0.225T RH - 6.838 \times 10^{-3}T^2 - 5.482 \times 10^{-2}RH^2 + 1.229 \times 10^{-3}T^2 RH + 8.528 \times 10^{-4}T RH^2 - 1.99 \times 10^{-6}T^2 RH^2 \]

Where:

\( HI \) — Heat Index (°F)
\( T \) — Temperature (°F)
\( RH \) — Relative Humidity (%)

Explanation: The formula accounts for the nonlinear relationship between temperature and humidity in how humans perceive heat.

3. Importance of Heat Index

Details: High heat index values indicate dangerous conditions that can lead to heat exhaustion or heat stroke. The NOAA issues heat advisories based on these values.

4. Using the Calculator

Tips: Enter the air temperature (°F) and relative humidity (%). Both values must be within valid ranges (T ≥ 0°F, 0% ≤ RH ≤ 100%).

5. Frequently Asked Questions (FAQ)

Q1: Why is humidity important for heat perception?
A: High humidity reduces sweat evaporation, making it harder for your body to cool itself effectively.

Q2: What's considered a dangerous heat index?
A: NOAA considers 103-124°F dangerous, and above 125°F extremely dangerous.

Q3: Does this work for temperatures below 80°F?
A: The formula is most accurate above 80°F. Below this, the heat index equals the actual temperature.

Q4: How does wind affect the heat index?
A: The standard formula doesn't account for wind, which can increase perceived temperature at high temperatures.

Q5: What's the highest possible heat index?
A: In extreme conditions (T=130°F, RH=90%), the heat index could reach 175°F, though such conditions are extremely rare.