Heat Wave Meaning

(US, weather broadcasting) Three consecutive days with daytime high temperature of 90 degrees Fahrenheit or higher.

Example: 1933, Irving Berlin, "Heat Wave", As Thousands Cheer
  We're havin a heat wave / A tropical heat wave / The temperatures rising, it isn't suprising / She certainly can, can can! / She started a heat wave / By letting her seat wave, / in such a way that the customers say / that she certainly can, can-can!