The southern coast of Maui generally sees water temperatures around 72 in the winter up to 77 in the summer. We have tradewinds consistently in the afternoons (often claim to set our watches by them) so you want to be in the water early and out around 11:30. Sometimes after a rain groundwater will flow into the ocean and create a cold lens, but this typically only sits on the first 2 feet of the surface. There isn't a huge thermocline here so water at 100 feet will only be 1-2 degrees cooler than at the surface.
In the middle of the island is an area called Olowalu and Coral Gardens which can be reached from shore and is protected from almost everything except direct north-traveling swell, so is often a good place to dive in the late morning. In the afternoon there are only a few places that might be good for diving, mostly in Lahaina against the lee of the West Maui Mountains. Old Airport and Black Rock are decent early afternoon dives.
The tradewinds usually recede a little after dark, so if you are planning a night dive try to hit the water right around sunset and things should be calm by the time you get back out of the water (though this isn't always the case and you should definitely dive well within your limits on a night dive).
The north shore is slightly more accesible in summer when south-traveling swell is light, but the water is often colder because of the rainwater and runoff, usually around 68-70. The north shore tends to be less full of colorful critters, but tends to have more swimthroughs and structure.
In the middle of the island is an area called Olowalu and Coral Gardens which can be reached from shore and is protected from almost everything except direct north-traveling swell, so is often a good place to dive in the late morning. In the afternoon there are only a few places that might be good for diving, mostly in Lahaina against the lee of the West Maui Mountains. Old Airport and Black Rock are decent early afternoon dives.
The tradewinds usually recede a little after dark, so if you are planning a night dive try to hit the water right around sunset and things should be calm by the time you get back out of the water (though this isn't always the case and you should definitely dive well within your limits on a night dive).
The north shore is slightly more accesible in summer when south-traveling swell is light, but the water is often colder because of the rainwater and runoff, usually around 68-70. The north shore tends to be less full of colorful critters, but tends to have more swimthroughs and structure.
