FACT CHECK: Is Hurricane Irma the most intense hurricane ever?

>> RELATED: Live updates on Hurricane Irma

First, you have to understand how the entire Atlantic Ocean region is segmented by the National Hurricane Center. It’s divided into four sections:

Hurricane Irma is the strongest, most intense hurricane ever to exist in the section known as the Atlantic Basin, with sustained winds of 185 mph and atmospheric pressure of 913 barometers, Vrydaghs said. But not the strongest if you look at the entire Atlantic Ocean region, including the Gulf of Mexico, Caribbean, and East Coast sections.
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Here’s how Hurricane Irma stacks up among all hurricanes in the entire Atlantic region:

#1: Hurricane Wilma - 185 mph winds, 882 pressure (October 2005, Florida)

#2: Hurricane Allen - 190 mph winds, 899 pressure (August 1980, Texas)

#3: Hurricane Irma - 185 mph winds, 913 pressure

The severity and intensity of hurricanes is determined by two factors -- atmospheric pressure and wind speeds. The lower the atmospheric pressure, the more intense a storm becomes. As pressure rises, a storm begins to weaken, Vrydaghs said.

What is atmospheric pressure?

It’s sometimes referred to as barometric pressure, and for the most part is the same. Think of it as the weight of the air on the Earth.

If Hurricane Irma strikes the United States at its current intensity, it would become only the fourth Category 5 storm to hit the U.S. mainland since 1851, according to the National Hurricane Center.

Here’s a list of Category 5 storms that have struck the U.S. mainland:

Source: National Hurricane Center