Heat Index: Explained
Texas has experienced high temperatures this summer, and it always feels even hotter when standing outside.
You hear meteorologists talk about the heat index, but what does it actually mean?
What does heat index mean?
The heat index is a measure of how hot things feel when you factor in relative humidity.
The heat index is how hot it feels when outdoors, instead of the actual air temperature.
How is heat index calculated?
Want to calculate the heat index yourself? Here's a formula for you put together by Lans P. Rothfusz:
HI = -42.379 + 2.04901523*T + 10.14333127*RH - .22475541*T*RH - .00683783*T*T - .05481717*RH*RH + .00122874*T*T*RH + .00085282*T*RH*RH - .00000199*T*T*RH*RH
This isn't even the entire calculation, there are several adjustments based on certain conditions.
Seems easy, right?
If you don't want to break out your calculator, just know that it's a derivation based on the temperature and the relative humidity.
Why is the heat index important?
FOX 4 Meteorologist Ali Turiano said sweating in high temperatures is the body trying to cool us down.
High temperatures and a high heat index increases the moisture in the air which slows down the sweating process.
What happens when you stay in the heat to long?
As the heat index increases, the danger increases as well.
There are specific effects the heat index can have on a person as it rises. High heat exposure or doing outdoor activities can cause different symptoms depending on the heat index.
The National Weather Service issues warnings based on how hot the heat index gets:
- Caution (80 degrees to 90 degrees): If you stay in the heat for long periods of time or are doing outdoor physical activities, you may start to experience fatigue.
- Extreme Caution (90 degrees to 103 degrees): Possibly experience heat cramps, heat stroke, or heat exhaustion.
- Danger (103 degrees to 124 degrees): Increased chances of heat cramps or heat exhaustion. Suffering from a heat stroke is still possible.
- Extreme Danger (125 degrees or more): When the heat index is this high, spending too much time in the heat will likely cause a heat stroke.
Texas has experienced heat index's classified in the danger zone (103 degrees to 124 degrees) this summer.
What is the difference between heat exhaustion and heat stroke?
Heat exhaustion symptoms:
- Experiencing dizziness or feeling faint
- Excessive sweating
- Clammy, pale, or cool skin
- Nausea or vomiting
- Quick or weak pulse
- Muscle cramps
If you experience symptoms of heat exhaustion, drink water and move to a cool place.
Heat stroke symptoms:
- Throbbing headache
- No sweating
- Hot, red, dry skin and a body temperature of over 103 degrees
- Nausea or vomiting
- Quick, strong heart rate
- Possibly a loss of consciousness
If you show signs of a heat stroke call 911 and immediately try to get cool.