Coolant temp gauge should rise to the middle and stay there, period. It is NOT normal for it to go any higher (or lower) than the center of the gauge while the car is running. If it is hot and you shut it off, the coolant temp will rise slightly. In this case the needle may rise maybe 1 or 2 needle-widths above center, but should return soon after the engine is started, probably within 1 minute.

If the gauge is going higher than the center, you should verify that the electric fan is running on high speed during that time. If not, the fan, fan switch, fuse, or wiring is faulty. The other possibility is the gauge is just lying to you. You should probably just change the Coolant temp sensor first to be sure. They are very cheap. If CTS and fan operation is good, you should make sure the system is properly bled of all air.

Our cooling systems should be quite adequate at even 100F with the A/C on if everything is working properly.