Why You're Feeling So Hot And Miserable

It's Not The Humidity, It's The Dew Point That's Making It Stifling

LABELLE, FL. -- You've been able to take the summer heat all through June and the beginning July, but this week you're feeling miserable outside of an air-conditioned building. Why is that? The temperature, the humidity?

Most people think high humidity is why they feel miserable. Well, that's not exactly the truth of the matter.

It's not just the humidity that making you feel stressed. Relative humidity numbers actually are the highest early in the morning when the air is more saturated with moisture, as the sun obviously hasn't been able to burn off that moisture. But mornings are often very pleasant feeling. So what's going on here?

It's really the dew point that's causing the discomfort our body feels, the the abnormally high "heat index" numbers we see on weather reports.

The body is normally at about 98.6 degrees, so if the temperature of the air is well below that, it's able to use the skin and perspiration and any breeze blowing across the skin to keep one feeling cool. But, as the temperature rises, the "dew point" of the air also rises significantly, (that being the temperature at which if would rain or fog if the temperature fell to that point.)

A temperature of 90 degrees, and a dew point of 55 to 60 would feel comfortable, but when the dew point reaches 70 to 75, a typical situation in South Florida, you're feeling pretty bad! The higher the dew point the more humid it is, and your body is not able to cool itself down to meet the increased air temperature without more cooling breezes or evaporating moisture from the skin to keep the body comfortable

Summer Dew Points And How You Feel (courtesy of Washington Post)

Dew point	How Humid it Feels (and subjective description)
Below 55	Dry (Pleasant)
55-60	Hint of humidity (Still comfortable)
60-65	Moist (Tolerable)
65-70	Sticky (Becoming unpleasant)
70-75	Muggy (Gross)
Above 75	Sultry (Oppressive and unbearable)

Some of the consistently highest dew points in the U.S. are found along the Gulf Coast and in Florida. When dew point reaches the 70s that's when your body has a rough time keeping cool, and feels more uncomfortable as the dew point climbs.

The solution to staying comfortable (if you're not able to lower the dew point by going inside an air-conditioned space) is to find a way to cool the skin even when the dew point has risen. Start with fans blowing on yourself if inside a not air-conditioned space. 

When outside go to a shady place with a breeze blowing on your skin. Patting bit of water on your skin, allows cooling evaporation to take place, lowering your body's unpleasant feeling considerably.

When to shut or open the windows in a space that's not air conditioned?  A personal guideline for open vs. closed windows is to close them when the temperature is above 78 degrees or the dew point is above 57.

To find your current Heat Index, or how hot your body feels go to your favorite online weather service or try the National Weather Service's weather prediction service to calculate your own.

Florida Heat Index Map - Where It Feels Really Hot

To Calculate The Heat Index - "How Hot Your Body Feels"  from the National Weather Service.