NEW YORK - The National Weather Service has issued a heat advisory for all five boroughs as heat indexes reach near 97 degrees.

Mayor Bill de Blasio says the city is conducting homeless outreach in an effort to keep the most vulnerable New Yorkers safe. The city will also offer refuge to single adults at any homeless shelter, officials say.

There are a number of cooling centers open across the city in places like public libraries and community centers. 

Swimming hours at the city's Olympic- and intermediate-sized pools have also been extended until 8 p.m.

The National Weather Service is expected to lift the advisory Friday evening.