Having lived in St. Petersburg for almost 9 years, I can truthfully say that anytime is a good time to visit. Yes, we get some cold days (for us) in December and January...maybe even in the low 30's which is rare and usually only lasts a few days. And yes, we get some real scorchers...sometimes close to 100 degrees F. but these are few and far between and usually come in August. Our sea breezes usually keep it a comfortable 60-70 in the winter and mid 80's in the summer. But you want perfect? Come to St. Petersburg in the Spring....maybe in April or May. At that time of year, most of our "snowbirds" have returned north and we have less traffic; our lovely purple jacaranda trees are in their glory; our skies are a beautiful cloudless blue; and it is wonderful to be outside enjoying all that Paradise has to offer.