Boston Mayor Kim Janey has declared a heat emergency in the city ahead of what is the first heat wave of 2021.The heat emergency in Boston began Sunday and will last through Tuesday.StormTeam 5 says temperatures are expected to hit 94 degrees Monday, followed by a high of 91 degrees on Tuesday.To help city residents stay cool, cooling center are open at Boston Centers for Youth & Families community centers from 10 a.m. to 6 p.m. through Tuesday.“It will