Swelteringly hot.
Hotter than hell.
Stupid hot.
That part of summer where the underboob swamp thing never actually goes away. Hotter than cats on tn roofs.
Y'know: as hot as the teaspoon used to liquify powdered drugs. Duh.
Tommy, get up and hit the fan on, it's hotter than a teaspoon in a trap house in here!