There is a specific criterion that the South African Weather Service applies to each town or city, in order to determine whether heat wave conditions are met or not.
The criterion reads as follows: If the maximum temperature at a particular town is expected to meet or exceed 5 degrees C above the average maximum temperature of “the hottest month” for that particular place, as well as persisting in that mode for 3 days or more, then a heat wave may be declared. For ease of use by SAWS meteorologists, a detailed map of the “heat wave threshold” has been compiled (see figure 1 below), using the latest climatological data to hand. This threshold is thus the maximum temperature which needs to be met or exceeded, for a heat wave to occur.
Heat wave temperature thresholds over South Africa
Heat wave precautions
a. Stay indoors in a well-ventilated or air conditioned room.
b. If working outside, wear protective clothing (head-gear, etc.) and take breaks at regular intervals.
c. Avoid playing strenuous sports or engaging in excessive manual labour, as one runs the risk of heat exhaustion or sunstroke.
d. Dress in cool, lightweight clothes which are not constricting.
e. The wearing of hats (preferably with a wide brim) as well as the generous application of sunblock should be encouraged if one is outdoors for any length of time.
f. Remain adequately hydrated by drinking plenty of liquids (not alcohol).
g. Outside playtime for children should ideally be restricted or prohibited between 10:00 and 16:00.
h. The aged as well as infants are particularly vulnerable to dehydration and/or heatstroke and should be afforded extra care and attention during prolonged spells of hot weather.