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The danger in this week’s heat is its timing. Heat-related illnesses and hospital visits tend to rise in the first few days of 85-degree weather, before bodies have adjusted to summer conditions, according to guidance posted by Winchester — and the season’s first serious heat arrived at noon Thursday.
The National Weather Service office in Norton has placed a swath of central, eastern, northeastern and southeastern Massachusetts and northern Rhode Island, taking in Middlesex County communities from Lowell to Cambridge, under a heat advisory from noon Thursday to 8 p.m. Friday. Forecasters expect heat index values as high as 98 and warned that the combination of hot temperatures and high humidity may cause heat illnesses.
Winchester is directing residents who need relief to two air-conditioned buildings, the Winchester Public Library and the Jenks Center, both open as cooling spots during business hours. The town’s guidance notes that anyone can be affected when heat and humidity make it harder for the body to cool itself, but older adults and young children face higher risk, along with outdoor workers, people who are pregnant and people with chronic health conditions.
The heat index measures how hot it actually feels by combining air temperature and humidity, and it describes conditions in the shade. In direct sun, the National Oceanic and Atmospheric Administration (NOAA) says, the same air can feel up to 15 degrees hotter. A heat index between 90 and 103 falls into NOAA’s extreme caution range, where heat stroke, heat cramps and heat exhaustion become possible risks after long exposure or exercise.
Winchester’s discomfort is part of a much larger map. About 37 million people — 11% of the population of the contiguous United States — live in areas forecast to reach dangerous heat levels Thursday, according to NOAA data, with the worst conditions concentrated in Texas, the mid-Atlantic and the Southeast, where heat index readings of 106 to 109 are forecast in cities including Laredo, Texas; Baltimore and Norfolk, Virginia.
Relief is close. In Haverhill, north of Boston, NOAA forecasts show the heat index falling from 94 Thursday to 90 Friday, 86 Saturday and 80 by Tuesday, a pattern expected across the region once the advisory expires Friday evening.
Until then, the weather service is asking people to drink plenty of fluids, stay in air-conditioned rooms and keep out of the sun. Its last instruction is the one aimed at the days before bodies adjust: check on relatives and neighbors, especially older people and those who live alone.
