Friday is an ozone action day, and an excessive heat watch follows for Saturday and Sunday.
Daily high temperatures in the 90s are forecast through late next week at Lehigh Valley International Airport, according to the National Weather Service.
The weather service issued an excessive heat watch that calls for caution. It's in effect from Saturday morning through Sunday afternoon for a region encompassing Lehigh, Northampton, Warren and Hunterdon counties.
In addition, Friday is forecast as an ozone action day in the Lehigh Valley. Children and adults and people with lung disease such as asthma are advised to reduce prolonged or heavy exertion outdoors, according to airnow.gov.
"It's a pretty extended heat wave," National Weather Service meteorologist Al Cope said of the forecast through next Thursday. "There's no big cool-down in the foreseeable future."
Food for thought... through July 20th, 2015, Allentown, PA reached 90degF five times. So far this year: 13 times. Should hit 20 in a week.
-- EPAWA Weather (@epawawx) July 21, 2016
For the weekend, the excessive heat watch says to expect highs in the middle-to-upper 90s Saturday and mid-90s Sunday.
Factoring in relative humidity to air temperatures, the heat index forecast is even hotter: 98 to 103 on Saturday afternoon across the advisory area covering eastern Pennsylvania and much of New Jersey.
"Heat index values may briefly approach 100 on Friday afternoon," according to the excessive heat watch. "Monday has the potential to be just as hot and humid as Saturday. The watch may need to be extended."
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Forecasters see a high potential for heat-related health issues, particularly for the elderly and those in poor health, according to the advisory.
"An excessive heat watch means that a prolonged period of hot temperature and high humidity is expected," the weather service says. "This combination will create a dangerous situation in which heat-related illnesses are possible.
"Drink plenty of fluids, stay in an air-conditioned environment if possible, stay out of the sun and check on elderly relatives and neighbors.
"Keep pets in a cool location with plenty of available water."
UGI Utilities Inc. offers the following tips on conserving energy during a heat wave:
- Close blinds, shades and draperies to keep out the sun's heat and help fans and air conditioners cool more efficiently.
- Close doors leading to uncooled parts of your home.
- If you have central air conditioning, close off vents to unused rooms. Keep filters clean.
- Use appliances such as washing machines, dryers and dishwashers after dark to help reduce peak energy demands.
To blame for the heat is high pressure aloft over the middle of the United States, blocking any flow of cooler air, said Cope, from the National Weather Service.
"Once they set up, they're kind of hard to get around," he said. "These heat episodes tend to be kind of dry also. It just kind of sustains itself."
Kurt Bresswein may be reached at kbresswein@lehighvalleylive.com. Follow him on Twitter @KurtBresswein. Find lehighvalleylive.com on Facebook.