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What are dew points? And how they make Florida summers so muggy.

Dew on a window.

A recent stretch of warm and muggy weather has brought extreme heat to much of the United States, including here in the Sunshine State.

All one has to do is turn on a newscast to hear a meteorologist discussing how humid it feels. Occasionally, the meteorologist will show a map with dew point numbers on it. What exactly does a dew point number represent? Is it the same as humidity?

"The dew point is the temperature the air needs to be cooled to at constant pressure in order to achieve a relative humidity of 100%." This official definition is courtesy of the National Weather Service and while it contains some technical verbiage, the bottom line is dew point is a more accurate measure of how much moisture is in the atmosphere. But why is dew point a better indicator for atmospheric moisture?

Relative humidity fluctuates throughout the day and is highest during the morning hours because the air temperature and dew point tend to be close. For example, an air temperature of 30 degrees and a dew point of 30 degrees will give you a relative humidity value of 100%. What happens if we change the air temperature and dew point and how would it impact relative humidity values? Let's say the air temperature was raised to 80 degrees and the dew point was bumped to 60 degrees. This would give a relative humidity value of only 50%.

Using this example, it becomes clear to see why using dew point is the preferred way of properly demonstrating how much moisture is in the atmosphere at any given time. Dew point numbers tend to be comfortable at 55 degrees or less. Between 55 and 65 degrees, the air becomes muggy or "sticky." In Florida during the summer months, it is not uncommon to find dew point numbers well into the 70s. This is when the air almost feels heavy because of the moisture content of the atmosphere. When one combines high dew points with warm temperatures, it can be a dangerous recipe for potential heat-related illnesses.