First of all:
Air temp and humidity are ALWAYS relevant. They effect HP so they are very important to consider.
Secondly:
HP is HP, it doesn't matter where in the world you are, only how accurately you measure it and if you don't calculate HP with air temp and humidity involved, your readings are inaccurate. We measure in HP also. We also measure using the metric system of KW but it doesn't matter which reading you take, they are both accurate.
Your buddy actually has 400-420hp at the wheels if its still standard weight