'Relentless' heat wave to grip northeastern US into July 4

The unfolding heat wave across the northeastern United States may be especially taxing on residents since there has not been such a stretch of temperatures this high since 2016, and in some cases even longer.

Days of highs in the 90s F with dangerously higher AccuWeather RealFeel® Temperatures are expected to grip many communities in the Northeast through at least July Fourth.

The sweltering conditions will continue at night, especially in the major urban areas where temperatures may not fall below the middle or upper 70s.

"The vast expanse of concrete, pavement and brick will give off heat through the night," AccuWeather Senior Meteorologist Alex Sosnowski said.

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The added strain of dealing with days of heat and humidity can lead to higher energy costs and an increasingly greater threat of residents suffering heat-related illnesses.

As the heat also encompassed southern Ontario and the St. Lawrence Valley, CBC News reported that more than 50 people were treated for heat-related issues at Canada Day events in Ottawa.

"It will not only be very hot, but it may also be perceived as relentless for many people in the Northeast as the heat lingers into the first part of July," AccuWeather Long-Range Meteorologist Paul Pastelok said.

"Last summer, the longest stretch of 90-degree days was mostly in the four- to five-day range for areas north of the Mason-Dixon Line," he said.

This heat wave can range from six to eight days in many communities. This includes Burlington, Vermont; New York City and Albany, New York; Hartford, Connecticut; Philadelphia; and Washington, D.C.

A heat wave across the northern tier of the U.S. is defined as three consecutive days of highs at or above 90 degrees Fahrenheit.

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The longevity of the unfolding heat wave can rival the hot spells from 2016 in some communities. In other communities, such a prolonged heat wave has not occurred since the early years of this decade.

Philadelphia recorded a heat wave that spanned eight days in 2016, but New York City has not endured consecutive 90-degree highs for a week straight since 2013.

During the summer of 2017, Pittsburgh did not record even two back-to-back 90-degree days. Even if temperatures stop short of 90 on Monday, the city is still on track to endure an official heat wave the following three days.

Heat is now coming back with a vengeance. Record highs will again be challenged on Monday as the heat wave reaches its peak intensity.

Philadelphia will join some other communities in recording highs near or at the century mark.

"Temperatures have not reached 100 F in Albany since 1953, but the city will flirt with that mark again on Monday afternoon," AccuWeather Meteorologist Tony Zartman said.

Sweltering humidity will create dangerous AccuWeather RealFeel® Temperatures in excess of 100 F throughout the Northeast.

Heat to be trimmed briefly from eastern New England

A push of cooler air from the northeast can trim the heat from the New England coast and eastern Long Island on Monday.

Temperatures are expected to be held to the middle 70s in Portland, Maine, and the middle 80s in Boston. However, the break from the 90-degree heat will not extend to Boston's western suburbs.

Boston officially experienced its first heat wave of the year on Sunday as temperatures soared to 92.

Any heat relief in eastern New England will not last long with temperatures expected to rebound Tuesday.

The region will join most of the Northeast in experiencing highs from the upper 80s to the lower 90s for July Fourth. Sea breezes will help to keep the beaches cooler.

Tips to follow to avoid heat exhaustion and stroke

"People of all ages, regardless of their health and physical activity, indoors and out, will need to stay hydrated," Sosnowski said. "Intake of alcoholic beverages should be limited, especially when there is no means to keep cool, such as in air conditioning."

Wear loose and light-colored clothing and avoid strenuous activities during the midday and afternoon hours -- the hottest times of the day. For those whose jobs require physical outdoor labor, be sure to take frequent breaks.

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As the heat extended its grip on the Midwest, three players of the Minnesota Twins baseball team had to leave the game at the Chicago Cubs' Wrigley Field due to heat-related illnesses on Saturday, according to the MLB.

Ensure that the elderly, children, homeless and pets are finding ways to stay cool. Remember never to leave a child or animal in a sealed vehicle without air conditioning even for a short time. Vehicles can become dangerously hot in a matter of minutes.

"Cooling stations will be warranted as heat builds to dangerous levels in the urban areas of the major cities," Sosnowski said. "Air stagnation and poor air quality are a concern with this heat wave."

There is a risk of brownouts due to higher energy demands. Help conserve electricity by turning off fans and air conditioners when leaving home.

Spotty afternoon thunderstorms may dot places west of the Appalachian Mountains on Monday before an uptick in widely separated thunderstorms occurs over other parts of the Northeast Tuesday into Independence Day.

Most of the thunderstorms on Tuesday and Wednesday should occur during the afternoon and diminish prior to July Fourth fireworks shows.