Rabbits and guinea pigs are extremely heat sensitive. They should be kept indoors when you know weather is going to be hot. They dehidrate very easily and can die in temperatures of even 33 C and in days of high humidity. Don't take any chances with them. Keep them safe indoors. Don't overfeed them in hot days, change water regularly so they have access to cool water. Feed them a bit of vegies or fruit with some water content like celery tops, little apple dices, bok choy during hot days. You can put an ice block inside the cage on these days and you can sprinkle them with a bit of cold water during the hottest part of the day. Keep them in room well ventilated, with blinds or curtains shut - no direct sunlight when hot. If you go away from October up to March - hot months - keep them indoors. They take time to get used to sudden hot weather so the initial Spring heat waves can be quite dangerous.