Tropical humidity will exacerbate the already toasty temperatures, the sauna-like warmth keeping nighttime temperatures from providing relief, which poses health risks to anyone without access to cooling, especially vulnerable populations such as those with preexisting medical conditions and the elderly.
The heat wave is coming on top of the coronavirus pandemic, with a recent uptick in cases of the novel coronavirus in Virginia, Maryland and the District, complicating public health planning.
The community spread of the coronavirus presents complications for communities seeking to provide cooling shelters for residents, especially since the heat will target some of the same groups that are experiencing disproportionate impacts from the illness, including poorer residents, minorities and the elderly.
The regional breadth of blistering heat is part of a larger area of unusually high temperatures that encompasses the central and eastern portions of the Lower 48. On Friday, heat advisories and warnings stretch from the Dakotas down to Texas and eastward into Indiana. In states such as Iowa, moisture evaporating from crops across the Corn Belt will contribute to building extreme humidity, amplifying the heat to bring heat indexes topping 110 degrees.
Locally, the National Weather Service has already hoisted an excessive heat watch for much of New Jersey, eastern Pennsylvania and northern portions of the Delmarva Peninsula. Peak heat index values between 105 and 110 degrees are possible in these areas during the Sunday through Tuesday period. The NWS may issue a heat advisory for the DMV on Monday, forecasters stated.
The heat will also affect New York City, but the Big Apple looks to remain on the periphery of the atmospheric torch aimed to its south.
About 283 million Americans could see high temperatures top 90 degrees during the next week, while more than 20 million could see highs top 100 degrees during the same period.
Local heat could will go from uncomfortable to dangerous
The elevated temperatures stem from a strong, sprawling area of high pressure anchored over the Tennessee Valley, also referred to as a “heat dome.” Beneath it, sinking air will warm well into the 90s. Dew points, meanwhile, will climb above 70 degrees. Dew points are a measure of how much moisture the air contains; and dew points in the 70s make the air feel oppressive.
In the D.C. area, the clockwise flow around the high pressure will bring westerly winds, which will further elevate air temperatures by causing air to spill over the Blue Ridge and sink to lower elevations. That compression increases its air pressure, and in turn its temperature — allowing for further warming.
The sweltering weekend could feature highs in the upper 90s for D.C. both Saturday and Sunday, with the National Weather Service forecasting a 100-degree high on Monday. The heat index, which is measure of how hot the air feels to the human body, could be as high in the DMV as it will be in Phoenix, thanks to the copious amounts of moisture in the air along the East Coast.
The heat is going to be noteworthy for both its severity and endurance. Highs in the upper 90s could linger through at least the mid week, with the only relief coming from periodic afternoon showers and thunderstorms. Adding insult to injury, the heat wave follows D.C.'s second-longest stretch of 90-degree days, which ended Thursday when the high temperature at Reagan National Airport only reached 87 degrees.
“Monday [is] looking to be the hottest day next week with triple digit readings certainly possible across portions of the metros and northern Virginia,” wrote the National Weather Service in Washington. “Combine this with dew points in the low to middle 70s, [and] heat indexes will likely be hovering near Advisory level range both Monday and Tuesday.”
Regardless of whether the District hits the triple digits on Monday, it will still fall shy of a daily record. The city managed a remarkable high of 106 degrees on July 20, 1930. However, D.C. hasn’t snagged a 100-degree reading since 2016, when temperatures hit the century mark on three consecutive days between August 13 and 15.
Heat waves can be deadly
In many years, extreme heat is the number one weather-related cause of death in the United States, topping tornadoes and hurricanes. In addition, heat waves are one of the clearest manifestations of human-caused global warming, with studies pointing to an increase in both the occurrence of these events as well as their severity.
The elevated overnight temperatures forecast during this heat event, with low temperatures remaining near 80 degrees in Washington on Sunday and Monday nights, poses a particular health risk. Exceptionally warm and humid nights prevent the body from experiencing a respite after a long, hot day, and this can more quickly lead to dehydration and heat-related illness.
Due in part to human-caused climate change, overnight temperatures are warming faster than daytime highs, which can prove especially problematic for urban residents who lack air conditioning. During this heat wave, people may be hesitant to go to cooling shelters for fear of contracting the coronavirus.
The long-range outlook does not offer much hope for a respite, either. Despite some moderation in temperature, above-average temperatures look to dominate much of the country for at least the next two weeks, if not longer.