Abby,
I would not use a cold pack regardless of temps for FL. Being that I've been here almost my whole life and I've shipped out dozens of snakes in different times of the year Ive never used a cold pack even when temps were in the 90's. My toughest shipment was an adult Carpet I shipped to Alaska about 2 months ago. The temp here was around 85 and the temp in the city of Alaska was in the high 30's. I put a heat pack in the box before I shipped and he arrived completely fine.
Cold packs are useless in my book, at least with Carpets and Boas that is. The only thing I use is heat packs when needed (generally if it's below 60 in any of the cities where the package will go through).
Just a note: When you ship and look at the weather, don't look at the high because the package will be delivered before the temp gets to that level. The main thing you want to look at is the low, the package will be traveling at night and in the morning so the high has nothing to do with the equation. When you go to your shipping facility go right before the pickup time (the FedEx I go to has a pickup time of 6:45pm), I get there at 6:30pm so even if the temp is a 98 high for that day, at the time I drop the box off it's in the mid 80's. That aside, being that your shipping TO Florida (not from Florida), when the package arrives and is delivered it will not be the 'high' for that day, it will generally be in the mid 80's (at this time of year) because the 'high' hits in the afternoon (yes it unfortunately hits the mid 80's by 10:30am). You can look at hourly weather charts to help you out if your concerened.
Also be sure to look at the connection flight. FedEx packages connect in Memphis TN so the things you look at are:
Your weather
Memphis' weather
Destinations weather
Look at the 'lows' NOT the 'highs', the package will never encounter the 'high' unless it gets delayed and then stays the whole day somewhere.
Sorry for such an elaborate post but thought I'd help others out who may be wondering about shipping too. Hope this helps!