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What is the difference between a heat advisory and an excessive heat warning?

With another heat wave expected in Hampton Roads, let's break down the definition of a heat wave and what criteria need to be met for heat alerts.

NORFOLK, Va. — Hampton Roads is entering another heat wave, but keep in mind that a heat wave is different than normal, hot summer days.

According to the National Weather Service, a heat wave is defined as a period of abnormally and uncomfortably hot and unusually humid weather. By definition, a heat wave has to last at least two days.

When the heat index, or feels-like temperatures, gets hot enough, then the National Weather Service can issue heat alerts.

RELATED: What's a heat index? Here's how feels-like temperatures are determined.

There are two types of heat alerts: a Heat Advisory or an Excessive Heat Warning. For a Heat Advisory to be issued for Hampton Roads, the feels-like temperature needs to climb to 105° or higher for at least three hours.

The criteria for an Excessive Heat Warning is even higher. For an Excessive Heat Warning to be issued, the feels-like temperature has to rise to at least 110° for at least three hours.

The kicker is the criteria for Heat Advisories and Excessive Heat Warnings change depending on where you live. 

Credit: 13News Now
Each region has a different criteria for heat alerts.

RELATED: How is a heat dome different from a heat wave? Here's what to know.

The further north you go, the lower the heat index has to be in order for a Heat Advisory to be issued. For example, in Boston, the feels-like temperature only has to be 95° for their local office to issue that alert.

When high heat is in the forecast and you plan to spend a long time outside, always make sure to drink plenty of water, take frequent breaks - especially if you can find some A.C. - and wear light-colored clothing.

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