Boston braces for extreme August heat

August is shaping up to be another scorcher, with the heat index this week expected to surpass 100°.

Driving the news: Boston Mayor Michelle Wu declared a heat emergency starting today through Sunday.

• The city has 16 cooling centers open, as well as splash pads spread around.
• Officials advise people to use face masks in the cooling centers because COVID-19 cases are rising.

Why it matters: Heat exposure can cause headache, cramps or life-threatening illness.

• During last month's heat wave, Boston EMS saw a 15-20% rise in daily 911 calls, according to the mayor's office.

Flashback: Boston broke records in July. Temperatures hit 100° on July 24, breaking the last record of 98​​° first set in 1993.

• The heat was so severe that Nantucket saw its warmest July on record, up 4.6° from the average of 75°.

The bottom line: Whether you're vacationing or stuck at work, try to stay cool.