Although it's all outside, it's very shady and there are ceiling fans that circulate air around. We ate there last week in the sweltering heat and we were still comfortable while eating because the shade and fans made it fine.
Flame Tree is a must-do for my family every year. We have always gone in September; and it has always been a comfortable place to eat due to all the shade.
We love the food at Flame Tree so unless it's very hot, we always plan to stop there. The different tiers of tables cut down on the noise and sitting outside is very relaxing.