The heat isn’t letting up after dark — and that’s the part that worries health experts most. A heat event sweeping much of the Eastern United States is producing not just dangerous daytime highs but unusually warm overnight lows, cutting off the window the human body depends on to cool down and recover.
During a typical hot spell, nighttime temperatures drop enough to give the cardiovascular and nervous systems a break. When that reprieve doesn’t come, the body carries the heat load from the previous day into the next — compounding stress hour by hour. Experts say that cycle is what turns a heat wave from miserable into medically dangerous.
Some daytime readings during this stretch are approaching record territory, though final tallies aren’t confirmed yet. Record-breaking days draw attention. It’s the warm nights that often do the quiet damage.
Older adults, infants, outdoor workers, and people without air conditioning face the sharpest risk. The body’s ability to shed heat drops when the surrounding air stays warm through the early morning hours — the period that normally offers the most relief.
Whether temperatures will ease before the holiday weekend remains unclear.
