Heat scorches the Mid-Atlantic Friday before the worst hits the Southeast

Washington Post

3 days ago

Around 100 million people are under heat alerts Friday, from coastal Maine to South Carolina and across much of the Midwest and lower Ohio Valley into the Mid-South. Additional alerts are likely in the Southeast as temperatures rise in coming days.
The primary cause is a large heat dome centered near the Carolina coast on Friday. It will intensify, meander westward and pump sultry conditions into the region through the weekend and into next week.
Cities under heat advisories on Friday include Boston, New York City, Washington, Norfolk and Raleigh; Dallas, Little Rock, Memphis and Louisville are also under advisory. In and around St. Louis and the Philadelphia area, extreme heat warnings are in place for heat indexes above 105.
Over the weekend, attention increasingly shifts to the Southeast to what the National Weather Service is calling a 'long duration and very dangerous heat wave.'
Several consecutive days of extreme heat — temperatures near 100, heat indexes around 110 — are possible through at least the next week in Alabama, Florida, Georgia and the Carolinas in particular. More concerning, overnight relief will be minimal.
Much of the Northeast is experiencing Friday's worst heat, with record and near-record afternoon temperatures possible from New England through the Mid-Atlantic.
Expected highs of 96 in Boston, 93 in New York's Central Park and 99 in Washington are about 10 degrees above average for the typically toasty time of year.
A forecast of 97 in Philadelphia would tie a record for the date; Newark, a typical hotspot in northern New Jersey, is forecast to reach a daily record of 100; Portland, on the south coast of Maine, could flirt with a record for the date of 91.
Many low temperature high marks are also in play. The high humidity — at extremes for longevity this summer in much of the region — keeps temperatures from falling too far, exacerbating health risks from prolonged exposure.
According to Climate Central's Climate Shift Index, a majority of the Mid-Atlantic and Southeast will experience daytime and nighttime readings at least 5 times more likely due to the effects of long-term warming.
Multiple days of the highest-end heat risk, Level 4 out of 4 — when widespread impacts to health, systems and infrastructure become likely — are forecast for a big chunk of the Southeast.
The worst conditions are expected from Georgia to North Carolina.
Some locations that will see lengthy stretches of dangerous heat include Raleigh, Atlanta, Jacksonville, Orlando, and Lynchburg, Virginia, among others.
Expanding to include major heat risk, or Level 3 out of 4, the region facing four to seven days of such grows to house most locations near and east of the Mississippi River and to the south of the Mason/Dixon line.
At that level, anyone without adequate cooling and hydration is at heightened risk for heat illness.
It will probably be the hottest weather of the year in Atlanta, where the maximum so far is 97. The forecast there calls for 99 on Monday and Tuesday, then 98 on Wednesday.
Similarly, Jacksonville is forecast to reach its hottest of the year. Monday's high is currently expected to reach 101, per the National Weather Service outlook there. Charlotte will also make a run for seasonal highs with several days near or above 100.
Other parts of the region could also see multiple days in a row at or above 100 degrees.
Numerous records are likely daily, from Florida through the Southeast, beginning Saturday and lasting through at least next Thursday.
Factoring in the high humidity, heat indexes will feel as much as 10 to 15 degrees worse than actual temperatures. That means values approaching and surpassing 110 in many locations, and on multiple days.
Places well positioned to see the highest heat indexes are big cities of the South and locations nearest the warm waters of the Gulf of Mexico, or the Mississippi Valley region.
Among cities with higher than 110 heat index in the forecast ahead, dew points — a measure of moisture in the air — will generally be in the 70s, which is at least borderline oppressive.
Some of the highest heat indexes in the outlook include: Nashville at 115, Jacksonville and Savannah with 113 and Huntsville at 111, Someone in the region could certainly see a heat index around 120 on the hottest of afternoons in this stretch.
With time, the heat dome center will shift westward, first toward the central U.S. and ultimately perhaps the 4-corners region.
This should open the door to a break in the hottest by this time next week. In fact, the East Coast could begin August cooler than normal in many of the same spots currently scorching.