Hi,
26 degrees here today, normal carb ratio sent me hypo within an hour of dinner - had the usual sort of meal, not extra fatty (as if that was possible) or anything.
Do split bolus if you suspect your insulin works better or kicks in faster in the heat.
Half at the start, half after 1 hour when you know what is going to happen.
Caught mine at 3.5 today. Had forgotten from last time how I seem to need 30 percent less NovoRapid. Won't make that error again tomorrow.
-M