What kind of icing did you use? If the water content was too high, then it may be why your fondant melted. Were they stored in the fridge? That could also be a reason for melting. Were they left out? Fondant doesn't normally melt so easily even in lots of heat and humidity but I suppose it depends on the fondant you use as well. Unless it was just the weather.
I live in FL and never had fondant melt on me but you could knead in a little tylose powder or mix 50/50 gumpaste and fondant..that will give your figures some stability.