As always - Women and children first - Take special care with pregnant does and does with litters. They overheat much quicker than other bunnies. If it gets too hot for them, bring them into the house or cellar during the day or a heat stretch. Remove extra fur from the nestboxes so the kits don't overheat.
Make sure the cage is in a shaded area with LOTS of ventilation. If inside a buiilding, pull down shades if the sun is beating in the windows. If no window shades, hang up a towel or thumbtack a grainbag up. Just don't obstruct airflow. Run a fan, preferably multiple fans. Keep the air moving even if it isn't much cooler. During real hot days, we run the front fan pulling in air, the back fan blowing air out and put an oscillating fan in the first aisle facing to the back and an oscillating fan in the last aisle facing front. Central Maine Power loves us!
If possible, put a soaker hose on the roof or hose the roof off. I was amazed when we had the corrugated plastic type of roof years ago and I hosed the roof. It lowered the inside temp about 10 degrees in about 5 minutes. In our current rabbitry, the ceiling is super insulated and the concrete floor helps keep it cooler.
Don't groom or handle your bunny during the heat of the day or have a lot of visitors in and out.
Yesterday when it cooled down before the thundershowers arrived, Patt-tee and I sat under the trees and enjoyed the 2nd day of June.