Water temps on the Bay Islands remain in the 79-82 range all year long. A much more important variable is the surface weather and conditions that you will have to endure during transit and the SI.
In the next few weeks, the weather will begin improving noticeably each day, not to mention the angle of the Sun. The storms which beat-up the North and Northwest sides of the island will have gone away for the season, the seas will be getting calmer, and there is less and less threat of rain.
Your surface interval allows for off gassing and just as important, for your physical body to get rest and warm back up. What would be better than a non- rocking boat, no wind, and of course... The warm Sunshine? AKR has very nice boats.
i would bring an unlined Goretx parka for the boat just in case, but that's a good item any time period. I appreciate that you asked "what will the water temps be" kind of question, versus the absolutely unknowable "what mil suit should I wear?" For that there is no answer other than from personal experience.
On Roatan, and certainly AKR, you can do a lot of repetitive diving, so this is another huge factor in deciding what to make of the otherwise predictable 79-82 degrees.
Please post a full report when you're able to.