99 Cav Overheating?

I recently bought a 99 Cav which has the standard instrument cluster. The temp guage has a low mark, high mark, and a red zone. I notice that while driving the temp guage stays right in the middle of the low and high marks but will quickly creep up to around 3/4 or 4/5 between the two marks in stop and go traffic or long idles. One particularly warm day, stuck in heavy traffic for construction, I watched it creep up to very close to the red zone. Note: It has never gone into the red zone. (The car does not have AC and I had turned off the fan for the air into the cabin.) Since I don't have much prior experience with this vehicle, I'm wondering: is this normal? Or am I heading for a problem that I could perhaps nip in the bud right now? With thanks to all who reply.