As a dome of sweltering heat, dense humidity and bright sunlight pushes eastward, experts are urging everyone, not just those at high risk, to take precautions.
"When you get all three together — heat, humidity and sun — it makes the trifecta, and it really increases your chances of getting ill," according to Stacey Talbert, a registered nurse at Meritus Medical Center emergency department.
The Maryland Department of Health and Mental Hygiene activated its heat emergency plan this week, warning localities and residents to prepare.
The National Weather Service has placed Washington, Franklin (Pa.), Jefferson and Berkeley (W.Va.) counties under an excessive heat warning today and Friday from noon to 8 p.m., forecasting temperatures to spike to nearly 100 degrees, with the heat index topping 110 degrees at times.
Heat is the No. 1 killer of all weather hazards, according to the Associated Press, but heat-related deaths and illnesses are preventable.
The best defense is air-conditioning and hydration, Talbert said.
"Stay indoors in a cooler climate, if possible," she said. "Water is always best, Gatorade is next best. And do not forget to check on elderly and disabled neighbors."
The symptoms of heat and respiratory illnesses are not far removed from those of a heart attack and should be treated with the similar seriousness, Talbert said.
"Humidity can cause shortness of breath, fatigue and blurred vision; heat can cause dizziness, lightheadedness, numbness or tingling," she said. "These can all be signs of heat-related illnesses."
When temperatures rise, humidity only makes matters worse.
Humidity makes it feel even hotter because the body, which cools itself by perspiring, has to work harder when the air is already moist, the AP reported.
The heat index — a measure of humidity combined with temperature — reflects how hot the air actually feels.
Starting today, heat indexes are expected to top 110 degrees, the weather service said.
In the approaching heat and humidity, elderly and children are at a high risk of illness, Talbert said. COPD, or chronic obstructive pulmonary disease, asthma and other respiratory illnesses can increase an individual's risk, she said.
Outdoor work also poses an additional threat. The weather service advised those who work outdoors to know the signs of heat exhaustion and heat stroke, to wear lightweight clothing and drink plenty of water.
"This is dangerous weather, especially when we have these guys and girls working around hot materials like asphalt," said Charlie Gischla, a spokesman for the Maryland State Highway Administration. "At SHA, we make very clear to our people and to our contractors to choose safety over productivity."
SHA supervisors are trained to recognize the symptoms of heat stroke and heat exhaustion. Workers have access to plenty of water and are encouraged to take frequent breaks in air-conditioned trucks, trailers or in shade, he said.
While some road work is done during the day, most of the state's paving is done after sunset, Gischlar said.
Nighttime, however, can bring little relief.
Even when the sun goes down, Talbert warned that the risk of heat-related illness can remain.
"Often there is still dangerous humidity in the air," she said.
Already this summer, the emergency room at Meritus has seen heat exhaustion cases, but not so many heat-stroke cases, Talbert said.
However, as the weather worsens this week, the hospital is anticipating an influx of respiratory cases, she said.
Anyone experiencing symptoms from the weather should get to a cooler climate, drink water and seek medical attention, she said.
"The faster you seek medical attention the better," Talbert said.
The Washington County Division of Emergency Services coordinates local response to a heat emergency, said Verna Brown, emergency management coordinator.
As of Wednesday, the county was not anticipating the need for additional manpower to handle heat-related calls. It also had not needed to open any emergency cooling centers.
"If we see an increase in heat-related calls, if we see calls for small, spontaneous fires, we will of course re-evaluate the situation," she said.