A long-lasting extreme heat wave reached its dangerous crescendo Tuesday, bringing the hottest day in a decade to some major East Coast cities and putting millions of already fatigued Americans at risk.

A life-threatening heat wave has enveloped the East Coast, hitting major cities with the worst of the high temperatures on Tuesday before relief moves in.

In several cities, including New York, Boston and Philadelphia, temperatures have hovered in the upper 90s, with heat indices exceeding 100°F.