2nd heat wave of 2021 to hit northeastern US

Fans and air conditioners that may have been idle over the past few days across the northeastern United States will get another workout as temperatures will be on the rise through Sunday. AccuWeather forecasters say the mercury will climb even higher by early next week, and many areas along the Interstate 95 corridor will experience the second official heat wave of the season.

Even though temperatures will pale in comparison to the unprecedented heat in the Northwest, and many in the region may feel that this is a typical time of the year for hot and humid conditions, temperatures will swing to 5-10 degrees Fahrenheit above average for late June in the Northeast.

"After a comfortable stretch of weather with lower temperatures and lower humidity, it will be a return to reality for the Northeast and mid-Atlantic as we head into the final days of June," AccuWeather Senior Meteorologist Dan Pydynowski said.

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Temperatures during the middle days of this week dipped to 5-15 degrees below average for late June. Typically, highs range from the middle 70s in northern Maine to the upper 80s in southeastern Virginia this time of the year.

As high pressure strengthens off the East coast this weekend, increasingly humid conditions will be pumped into the region. Despite the muggy conditions, much of the region will remain dry, unlike areas farther to the west. Rounds of thunderstorms could be heavy at times, cause damage and lead to flooding in parts of the Midwest into next week.

However, Accuweather meteorologists warn that with the increased warmth and humidity levels, some isolated pop-up afternoon showers and thunderstorms cannot be completely ruled out, mainly across the higher terrain.

And the sticky air will have staying power, too.

"Once the humid air returns this weekend, it will stick around for an extended period of time through much, if not all of next week," AccuWeather Senior Meteorologist David Dombek said.

The heat and humidity will ramp up even more by Sunday with cities like Boston, New York City, Philadelphia, Washington, D.C., Richmond and Roanoke, Virginia, all forecast to reach the 90-degree-Fahrenheit mark with AccuWeather RealFeel® Temperatures soaring even higher into the mid- to upper 90s on multiple days.

On Monday and Tuesday, hot and humid air will expand and intensify across the Northeast with AccuWeather RealFeel® Temperatures ranging from 95-100 from Maine to Virginia, while cities such as Boston, New York City, Philadelphia and Washington, D.C., may experience RealFeel® Temperatures peaking between 100-105 during the late-afternoon hours.

"A few daily record highs may be challenged over central and northern New England, especially Monday and Tuesday as temperatures climb well up into the 90s," AccuWeather Senior Meteorologist Brett Anderson explained.

As the heat builds, some mid-Atlantic cities are predicted to experience a full-blown heat wave, which is defined as three-straight days with highs of 90 or greater in this part of the country.

In Philadelphia, a five-day stretch of 90-degree highs is anticipated from Sunday to perhaps Thursday. The City of Brotherly Love has had one official heat wave so far this year when temperatures soared into the 90s from June 5 to June 7. The city took another run at a heat wave, but fell one day short on the days surrounding the start of summer, June 20.

Washington, D.C., is also forecast to have its second official heat wave this season, as temperatures are expected to throttle up and into the 90s each day from Sunday to Thursday. Previously, the only heat wave thus far was a three-day stretch of 90-degree temperatures from June 5 to June 7.

New York City is forecast to peak within a couple degrees of 90 from Monday through Wednesday. So far in 2021, the Big Apple has only had one official heat wave from June 7 to June 9.

Even though Boston isn't predicted to have an official heat wave, at least two days of highs in the 90s are projected. Temperatures are forecast to reach the upper 80s on Sunday and Wednesday.

AccuWeather meteorologists warn that residents that plan to be outside partaking in rigorous physical activity, including jogging and yard work, should do so with caution with the surge of heat coming up. Taking breaks, staying hydrated and avoiding the peak heat during the afternoon hours each day could mitigate the risks for heat-related illnesses.

The beaches may be the answer for those who are looking to beat the heat, as local sea breezes will take hold from the south coast of New England to the Delaware and Maryland beaches each afternoon bringing temperatures back toward more comfortable levels.

As temperatures soar early next week, many major East Coast cities will continue to add to their annual 90-degree-day tally for the season. Cities such as Richmond have had 14 days so far this year on which the temperature reached 90 or higher. Cities like Philadelphia and Boston have had eight 90-degree days, with the latter breaking its record for the year to date. Meanwhile, New York City has only had four days at 90 or higher.

The heat wave will surely add to the running total with a few more 90-degree days likely here and there during the first few days of July and the Independence Day weekend along the I-95 corridor.

In their annual summer forecast released back in April, AccuWeather forecasters called for more 90-degree days than normal in many metropolitan areas of the Northeast. Philadelphia typically endures 31 90-degree days, and this summer's projection is for 33-38. The nation's capital deals with 45 days at or above 90 on average each year, and 2021 could feature as many as 47, according to AccuWeather meteorologists.

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