Heat Index Calculator NOAA

NOAA Heat Index Formula:

\[ HI = c_1 + c_2T + c_3R + c_4TR + c_5T^2 + c_6R^2 + c_7T^2R + c_8TR^2 + c_9T^2R^2 \]

Heat Index (°F):

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1. What is a Heat Index Calculator?

Definition: This calculator computes the heat index (apparent temperature) using the NOAA polynomial formula based on air temperature and relative humidity.

Purpose: It helps assess the perceived temperature accounting for humidity's effect on human comfort and health risks.

2. How Does the Calculator Work?

The calculator uses the NOAA polynomial formula:

\[ HI = c_1 + c_2T + c_3R + c_4TR + c_5T^2 + c_6R^2 + c_7T^2R + c_8TR^2 + c_9T^2R^2 \]

Where:

\( HI \) — Heat Index (apparent temperature in °F)
\( T \) — Air Temperature (°F)
\( R \) — Relative Humidity (%)
\( c_1 \) to \( c_9 \) — NOAA-derived coefficients

Note: The formula is only valid when temperature is ≥ 80°F and relative humidity ≥ 40%.

3. Importance of Heat Index

Details: The heat index indicates how hot it feels when humidity is factored in with air temperature. High values increase risk of heat-related illnesses.

4. Using the Calculator

Tips: Enter temperature in °F and relative humidity in %. Both values are required for calculation.

5. Frequently Asked Questions (FAQ)

Q1: Why does the calculator show "N/A"?
A: The heat index is only calculated when temperature ≥ 80°F and relative humidity ≥ 40%.

Q2: What's considered a dangerous heat index?
A: NOAA considers 90-105°F as "extreme caution", 105-130°F as "danger", and >130°F as "extreme danger".

Q3: Why does humidity affect perceived temperature?
A: High humidity reduces sweat evaporation, impairing the body's natural cooling mechanism.

Q4: Can I use Celsius values?
A: No, the NOAA formula requires Fahrenheit inputs. Convert Celsius to Fahrenheit first.

Q5: How accurate is this calculation?
A: It's accurate to within ±1.3°F when used within valid parameters (T≥80°F, RH≥40%).