When the temperature is high, the bees will gather on the outside of the hive in a practice called bearding. This removes their body heat from the inside and helps cool the hive. Sometimes bees with gather like this before swarming, but in high temperatures this type of behavior is usually bearding.

My top bar hive Saturn on July 1, 2018 at 8 pm in the evening. Temperatures were above 95 F during the day, with a heat index near 110 F. Most of the bees are gathered above the entrance, though many are also hanging below the hive.