It will feel like over 100 degrees in Boston Friday

After a glorious stretch of weather these past few days, the heat is about to crank up. Boston could eclipse triple-digit territory for the second time this summer.

Boston isn't alone. There are 95 million people, from the Gulf Coast through the Midwest and up into Massachusetts, under heat related advisories, watches or warnings.

The past few days have featured near or slightly cooler than average temperatures. By Thursday, though, the sea breeze will hold off and temperatures are expected rise into the low 90s.

That will make 13 days this summer over 90 degrees so far. That might seem like a lot, but the record for 90-plus-degree days stands at 30 days back in 1983. (By the end of the century, Boston will likely have 60 days of 90-plus-degree heat, and could have 80 days or more. )

The heat peaks Friday, along with oppressive humidity. Here’s what’s to expect:

Historical context: We last hit 102 degrees on June 24, and the last time Boston saw two 100 degree days in one summer was 1952. The daily record to beat in Boston is 96 (set back in 1882!)

This is the kind of heat that can overwhelm our natural cooling system. Sweat simply can’t evaporate fast enough when the air is this humid. You know the drill at this point in the summer: hydrate, seek shade and air conditioning if you can, and plan strenuous or prolonged outdoor activities for early morning or late evening.

Heat is the leading weather-related cause of death in the U.S, causing more deaths than hurricanes and floods combined.

A cold front slicing southward will spark scattered thunderstorms during the afternoon and evening. They’ll be few and far between, but each one carries the potential for brief damaging wind gusts, brief localized flooding in torrential downpours and small hail and lightning.

Saturday: After Friday’s furnace-like blast, Saturday should feel downright mild. Highs slip back into the 80s (with upper 70s along the coast) under a veil of high, milky clouds.

Sunday: Don’t get too comfortable; the humidity returns. Look for 80s inland, with the sea breeze once again offering a cool ocean reprieve along Boston’s waterfront and Cape Cod. A few late-day showers or storms may sneak into western New England.

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