Acclimatize yourself gradually to warmer weather. Treat yourself gently for those first two or three hot days. Dress for summer. Light colored and lightweight clothing reflects heat and sunlight. Vary your thermal environment.
Physical stress increases with exposure time in heat wave weather.
Try to get out of the heat for at least a few hours each day. Put less fuel on your inner fires. Foods like proteins, that increase metabolic heat production, also increase water loss. Don't get too much sun. Sunburn makes the job of heat dissipation that much more difficult.