Turks water temperature drops a little in the winter. IDK exactly when:
From November to May the average temperature is 80 to 84 degrees (27-29 degrees celsius). Water temperature in the summer is 82 to 84 degrees (28-29 degrees celsius) and in winter about 74 to 78 degrees (23-26 degrees celsius). A constant trade wind keeps the climate at a very comfortable level.
There is an annual rainfall of 21 inches on Grand Turk and South Caicos, but as you go further west the average rainfall could increase to 40 inches. In an average year the Turks and Caicos has 350 days of sunshine.
Hurricane season runs from June 1 to November 30th.
Quick Facts about Turks and Caicos Islands Turks and Caicos Tourist Board
The best diving is at West Caicos and French Cay. Both are full of pelagics - at French Cay we saw at least one - and usually several reef sharks on
every dive. I honestly counted a dozen stingrays near one mooring - they were spread out in the sand at 40'. I shoot video and a couple let me get so close that they started to raise their tails to leave b4 I backed off. Lots of turtles, some large, a few grouper and once we heard but did not see dolphins chattering. Also basketball sized lionfish - and often cuda under the boat. There's fish everywhere - the wall is so close to most of the moorings that you dive down it - the currnent upwelling brings up a lot of life.
The only issue with it as a day destination from Provo is it's a full day trip - ops pick you up in the AM via van shuttle, drive you to the south side marina for a 45min. boat ride, provide 2-3 dives and lunch and bring you back around 2:30 - 4:30 if you do the third dive. There's also very good to excellent diving off Provo's NW Point - a five min. boat ride. And Grace Bay - I saw a marked dive boat moored out there one afternoon.
I suspect if conditions were going to be rough that would be on the crossing between the islands - it was a little rough when we did it in spring. Not enough to prevent it - but enough to notice one way. We were on the T/C Explorer so it wasn't as big an issue. Most of the moorings are up against the island(s) - some are really close - so they're likely protected once you get there. I don't remember any issues with reboarding the boat except once on a drift dive - the absurdity of using a 110' boat to drift dive was probably a lot of that...lol.
I know they have snorkel excursions on Provo - IDK any details. I believe there's one area on/near Grace Bay where your non-diver can do that. Grace Bay is really pricey though - it's one of the nicest beaches in the world and they know it. There is a Comfort Suites a block or two inland if you're going solo and looking for something reasonable.
If money's no option, Amanyara is really nice..lol Even have their own private dive operator.
Comparable might be the Caymans. Grand Cayman has a lot of great dives. Also some shore accessible snorkeling. Some both - you can simultaneously dive/snorkel the Kittiwake wreck with some operators - it was put down deliberately for that. Stingray City is one of the best 14' dives you can do, we had snorkelers on our dive boat also - SRC - not the nearby Sandbar snorkel where you mostly get mauled by rays in 5'. Turtle Reef is one of the better shore dives and it's also a known snorkel spot. I believe there's good snorkeling off both Cobalt Coast locations also - it's certainly shallow for a long way and the reef comes right up to the dock. Areas of Sunset House to the south also. The best diving is North Wall boat diving - in November they may not be able to get out there. The West side is almost as good - many of the known sites are there - and they can dive it pretty much all year unless there's a storm. And they move boats, dive the south as an alternative. One of the best dives we did there was to the south - the reef sees less traffic.
www.idivecayman.com for videos.
Equally as pricey as T/C - not sure which is worse. You're going in high season also. There is both a Comfort Suites and Sunshine Suites - both about a block from the beach. The CI$ is .80 to the U.S. dollar so that's a shock at first. The flipside is if you're cheap like us, alot of the fast food U.S. chains are there, BK, Subway, Dominos, KFC. And unless you eat waterfront every night - prices aren't any more expensive than other resort areas. Food prices were pretty shocking also - we thought we'd cook to save. Not really...
IDK much about the Sisters (LC and Brac) except they're pretty small and quiet. Most people who've done both say the diving at LC is better. Brac has a lot of shore diving options also if you've got a buddy. Either is generally reachable the same day thru Grand Cayman.