Diving in South Florida can be a year around sport. But water temps in January can get down to the low 70"s and in hind sight from say the waters off New Jersey that pretty warm. One still gets cold and this can lead to issues while diving.
So how do you maximize diving while keeping yourself comfortable? Having the right thermal protection for the dive environment is a big factor. Water draws heat away from the body 20 times faster then in air. Having the right wetsuit and it fitting right will make a big difference. Most people think that Florida is a year around 3mm suit state, but most experts will tell you that a 3mm wetsuit is only good to a low of 73 deg F. But if your doing multiple dives and the air temperature is cool, you body is working to stay warm in the water and out.
For those who dive a lot and may have less natural thermal insulation, a 5 mm may be the new standard suit for you cooler water diving. this will keep you comfortable down to the mid 60's.
How about hoods and gloves? Hoods help prevent heat loss from your head that is estimated to be 20 to 40 percent of the bodies heat loss. Gloves also help protect your fingers and reduces your loss of dexterity.
One must remember that the bodies main goal is to keep your core warm, so as the core gets cold it regulates blood flow to your outer extremities. So it is important to help the body out and protect those areas as well.
In between dives you need to rewarm the body to prepare it for the next dive. This may include peeling off the wetsuit, drying off and putting on a sweater. This will quickly allow your core to reheat.
Hydrate, Hydrate, Hydrate. Even in the cold, you body dehydrates and this causes your body to do more work with less resources.
For those wanting gadgets, technology is coming to help in the form of Thermal Garments. Many companies are now offering Thermal heated undergarments that work underwater, but they are still pricy. Check out www.heatedwetsuits.com for some examples.
If that's not in you budget, perhaps placing a heat pack against you chest near your core, can give the body that slight heat edge. Check out www.reusableheat.com for hot packs that are safe to dive with. Placing one in your suit for a dive may help you feel more comfortable thru the dive.
I guess when all else fails just wait till summer to dive. On the other hand that just take the fun out of being an avid diver. Maybe a semi-dry or drysuit is a must. But I'll let you make that call.