WeatherWhys for July 20,2016 from accuweather.com

The period when the sun is exerting its strongest rays north of the Tropic of Cancer is coming to an end. However, normal temperatures in the middle latitudes are just now reaching their peak. That is because the oceans and land continue to gain warmth for weeks after the summer solstice. Not until mid-August does outgoing heat energy begin to exceed the warmth retained by the land and sea.