Before I discuss what is going on, it is instructive to define a "heat wave." To be a heat wave such a period should last at least one day, but conventionally it lasts from several days to several weeks. NWSSo what's causing the extreme heat wave in the Southeast? Typically, a prolonged high pressure system results in heat wave conditions because formation of clouds is difficult and air sinks. According to the NWS-Atlanta, here are some of the all-time record highs for May:Atlanta: 97 degrees F in 1914 and 1941Athens: 100 degrees F in 1918 and 1926Columbus: 100 degrees F in 1916 and 1937Macon: 99 degrees F in 1898, 1953, and 1967I think that some of these records (and others) may be broken in the coming days.

Source: Forbes May 25, 2019 12:33 UTC