At the battle of Monmouth there was a massive heat wave.
Monmouth was the last major engagement fought in the north; it was
the longest battle of the war; and it was fought, as no other major
engagement, in stifling heat. None who survived the day would ever
forget the heat. With more than fifteen hours of sunshine, June 28
was the fifth day of a heat wave, which on the day of the battle
saw temperatures close to 100 deg. Fahrenheit. All together there
were 59 heat stroke deaths.