Delaware and the entire Mid-Atlantic are set to see a late spring heat wave that’s forecast to set records in Wilmington, with a heat index bounding well into triple digits.

A heat advisory goes into effect Tuesday morning. By Wednesday, that will turn into an excessive heat watch, meaning temperatures and humidity are expected to flare up into dangerous territory, with heat indexes potentially cresting 100 during that span.

Here’s what to expect this week in Delaware, as the mercury rockets to the top of the thermometer.

Delaware will keep getting hotter as the week progresses

Temperatures may already reach 90 degrees Monday in Wilmington and are forecast to keep going up through the week as a high-pressure system from the Carolinas comes to settle over the mid-Atlantic, according to meteorologist Sarah Johnson at NOAA’s Mount Holly/Philadelphia forecasting center.

By Friday and Saturday, temperatures are forecast to tie or break all-time records. The Wilmington forecast as of Monday morning calls for a record-tying 98 degrees on Friday, and a record-breaking 99 degrees on Saturday.

High humidity means the heat index could be above 100 starting Wednesday, which is what triggered the excessive heat watch. By Friday and Saturday, the heat index may get as high as 110, before a cold front is expected to slide in from the west on Sunday.

The heat wave will be especially notable because the weather will stay hot for a number of days, Johnson said, and because it’s occurring so early in the season before Delawareans have had time to acclimate to higher temperatures, exposing people to the potential risk of heat illnesses.

Where will the weather be hottest?

The heat wave will likely follow what meteorologist Johnson calls a “typical pattern”: It’ll be hotter in the city, not just during the day but overnight. The highest temps will be seen along the I-95 corridor from Wilmington to Philadelphia to Trenton, Johnson said.

Why? Pavement and buildings heat up fast, stay hot and create their its weather patterns, a phenomenon known as the urban heat island effect.

“You’ve got a lot of concrete, which tends to tend to absorb heat and then re-radiate it, especially at night,” Johnson said.

Cooler temps will be found where there’s greenery and shade, or by the coast — especially with lower water temperatures early in the season. That said, “by the beaches” really means by the beaches. Temperature relief only really extends a mile or two inward from the water. Beyond that? Just as hot again.

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What’s the heat index, and when does heat reach dangerous levels?

Put simply, when the body sweats, the perspiration evaporates, cooling the body. When the humidity is high, the sweat doesn’t evaporate as quickly and the body doesn’t cool itself as well. Therefore, the body feels warmer. The heat index represents the heat you’re feeling outside.

Here’s a chart to help you find out what the heat index is. You can also use this heat index calculator.

Caution is advocated when the heat index crests 90, and is considered dangerous when the heat index goes up above 103, as the weather service warns it may do between Wednesday and Saturday.

The heat will worsen as the week goes on, peaking late in the week and into the weekend. The heat index may range as high as 110 on Friday and Saturday, well into the “danger” zone. The early season heat events combined with the prolonged nature of it may cause an increase in heat-related impacts such as heat illnesses, according to NOAA.

What should you do during dangerous heat conditions?

• Drink plenty of fluids.

• Stay in an air-conditioned room.

• Stay out of the sun.

• Check up on relatives and neighbors.

• Take extra precautions when outside.

• Wear lightweight and loose-fitting clothing.

• Try to limit strenuous activities to early morning or evening.

• Take action when you see symptoms of heat exhaustion and heat stroke.

Heat wave: What to know when extreme hot weather is forecasted

Who is most vulnerable in the heat?

According to the National Weather Service, heat is among the leading weather-related killers. These are the groups most impacted by high temperatures:

• Young children and infants are particularly vulnerable to heat-related illness and death, as their bodies are less able to adapt to heat than are adults.

• Older adults, particularly those with preexisting diseases, take certain medications, are living alone or with limited mobility and are exposed to extreme heat can experience multiple adverse effects.

• People with chronic medical conditions are more likely to have serious health problems during a heat wave than healthy people.

• Pregnant women are also at higher risk. Extreme heat events have been associated with adverse birth outcomes such as low birth weight, preterm birth, and infant mortality, as well as congenital cataracts.

How to handle pets in the heat

When heat waves hit, dogs are also susceptible to heat stress and head strokes, according to the American Kennel Club.

If your pet is exposed to extreme heat, the AKC suggests getting your dog to a shady spot, applying ice packs under the dog’s front legs on their chest, and pouring cold water over their head and body. Dogs should be given water to drink. A cooling mat for the dog to sit or stand on would be helpful.

In addition, according to the American Kennel Club, with temperatures 85 degrees or higher for a sustained period, dog owners need to be careful with hot asphalt, pavement and sand. The hot surface can cause blisters on your pet’s paws.

This article originally appeared on Delaware News Journal: A June heat wave in Delaware may mean record temperatures