Dorothy, it really does depend on the air temperature I think. I've been to the Bahamas in January several times and the water temperature is too cold to swim, for me. If the sun is shining and it's warm you may be able to stand it. I've seen people snorkeling before. but they are not in the water long.
Once, (2000, I think) the skies were overcast and the wind was blowing so hard we used our towels as blankets and huddled in a hammock until the tender arrived to take us back to the pier.
Hopefully, the weather gods will cooperate for you and you can snorkel. I will be bringing my gear for sure, just in case.