Like the rest of Florida, Miami is very hot and humid during high summer with temperatures regularly in the high 30s and frequent rain showers. The winter is cooler and much drier. In December and January it can get (relatively) cool with daytime highs in the high teens and low twenties.

My preferred time of year to go is winter and early spring but if you are bounded by school holidays you may well end up there in August. Expect to be rained on and schedule in plenty of stops to have a cold drink.

It is also worth noting that Florida is in the hurricane belt. It is mercifully rare for a hurricane to make landfall in Florida but if you find yourself there when one is forecast, be sure to get regular weather updates and talk to your hotel about the best place to sit out the hurricane.