More than 58 million people are under a heat advisory (orange) or excessive heat warning (pink in the Northeast on Tuesday.)

Heat advisories are in effect across the Northeast this week as high pressure strengthens and temperatures climb. High humidity combined with the extreme heat will create heat indexes, or “feels like” temperatures, from 105 to 110 degrees, making it dangerous for some populations to spend time outside.

As of Tuesday morning, more than 58 million people in the Northeast were under some kind of heat-related advisory. Two regions in southern New England are under an excessive heat warning, including Springfield, Mass., Hartford, Conn., and Boston. The advisories extend from Northern Virginia to the Canada border.

Several school districts in Connecticut, where the heat index was expected to reach the low 100s, chose to dismiss students early Tuesday. In Washington, the heat index will peak at about 105 degrees Tuesday afternoon.

The hot and humid weather will last through Thursday and into Friday in some locations, before a cold front brings in cooler air from the north. Wednesday will probably be the hottest, with records in jeopardy in southern New England.

The National Weather Service issues a heat advisory when an extended period of extremely hot and humid weather is in the forecast. Particularly, the combination of heat and humidity will be stressful on the body and make heat-related illness more likely. Young children and the elderly are particularly susceptible to heat illness. The Weather Service recommends checking on elderly neighbors during heat advisories, especially if they don’t have access to air conditioning.

The Centers for Disease Control and Prevention recommends wearing light-colored and loosefitting clothing to prevent heat-related illness such as heat stroke. The easiest thing you can do is stay indoors with air conditioning, but if you have to be outside for work or other strenuous activity, drink extra water and take extra breaks.

Signs of heat exhaustion or heat stroke include dizziness, nausea, headache, lightheadedness, weakness or fast pulse.


Heat-index forecast for Tuesday afternoon.

Wednesday

Records are in jeopardy Wednesday as temperatures push into the upper 90s. Boston’s forecast of 99 degrees would break the record for the date, which stands at 96 degrees set in 1953. Providence also could break or tie its record of 95 degrees set in 1953.

Forecast temperature (heat index in parentheses)

  • Philadelphia — 95 degrees (101)
  • New York City — 95 degrees (103)
  • Providence — 96 degrees (103)
  • Boston — 99 degrees (105)
  • Portland, Maine — 86 degrees (90)

Thursday

Temperatures come down as a cold front drops in from the north. The high temperature Thursday depends on how fast the cold front arrives. If it’s slow, the actual temperatures could be higher than this.

Forecast temperature

  • Philadelphia — 91 degrees
  • New York City — 85 degrees
  • Providence — 90 degrees
  • Boston — 87 degrees
  • Portland, Maine — 79 degrees

Read more:

The pumpkin spice latte hits menus — just what we need in a heat advisory

Climate change ‘switchboard’ visualization shows every country on the planet turning red-hot