Grist: Americas coasts are melting. California has posted weather warnings for temperatures as much as 20 degrees above average, and yesterdays 97-degree heat in Manhattan demolished a 93-degree record that had stood since 1919. So with the sun turning cheeks the color of tomatoes and crotches into sweat swamps, its time to ask the question: Is this the hottest day of the year? Depends where you live. Most areas of the U.S. have already passed the date of their average highest annual temperatures....