0W-30 has essentially the same viscosity at 212 deg F as does 5W-30 (9.7 cST v. 9.9 cST) according to Mobil 1 literature.
Does this mean it could be used in summer just as good as 5-30? Probably.
Most engine wear is purported to be caused at start-up, so thinner is better.
I checked my engine oil temperature several times in the past using an accurate digital temp gauge and found it to be in the 180-190 deg range, so it seems reasonable to use 0W-30 even in Florida.
