MYRTLE BEACH, SC (WMBF) - When the WMBF First Alert Weather team describes the summer heat, they'll frequently mention the heat index and how it FEELS with the humidity.
The National Weather Service uses a mathematical formula to calculate the temperature that the heat will make you feel, combining the outdoor air temperature with either the dewpoint or the relative humidity.
It's important to note the difference between the terms "dewpoint" and "relative humidity (RH)."
Dewpoint is the temperature representing of HOW MUCH moisture is in the air, while RH is a percentage of how close the air is to saturation. RH can often be at 100% when it's raining, however, also happens regularly in the early morning when the temperature has dropped to the dewpoint.
Since RH can fluctuate throughout the day, while dewpoints remain steadier, most meteorologists favor using dewpoint to showcase how pleasant or muggy it will feel. A dewpoint over 65°F is when mugginess starts to be felt. Any dewpoint below 65° feels drier and more pleasant.
The conditions for heat index are based on how temperatures feel in the shade…meaning if you are in full sun, add another 10° to 15° to the heat index.
The highest heat index ever recorded was 178°F in Dhahran, Saudi Arabia on July 8, 2003 according to weather historian Christopher Burt in his book Extreme Weather. The afternoon air temperature was 108°F with a dewpoint at 95°F. Dhahran is located along the Persian Gulf in the Middle East.
A more recent extreme heat index of 168°F happened in Bandar Mahshahr, Iran according to the Washington Post Capital Weather Gang. The temperature was 115°F and dewpoint near 90°F, in the city located near the Persian Gulf.
The Heat Index is right at the top of the WMBF First Alert Weather App, along with current conditions, hour by hour forecasts and blogs from the First Alert Weather Ream. Download it FOR FREE today!