Well, today's your lucky day. I'm just returning home after a trip to Monterey and 2.5 days of diving in the Monterey area. The water is cold, but it's not the end of the world. I dove a 7mm (well, I think it's technically 6.5, I should check really) full wetsuit and wore a 7mm core-warmer (a thing that looks like what the olympic weight lifters wear but made of neoprene). I did 3 dives the first day and was a bit cold. I did two dives on the two subsequent dives and was always just fine. I could tell the water was cold, but I was still fine. During surface intervals, I would unzip and roll down the top of the wet suit, dry myself up and put on a light shirt and a sweater. You might want to bring a hat, just in case. I've seen many people dive dry, although I did meet local divers diving wetsuits. I would say that if you're doing 2 dives in a day and then no more, you may well be fine in a wetsuit.
You can rent steel cylinders in Monterey with no problem. I used AL80s for the first 2 days and Steel whatever (was my first time using steel cylinders, the initial pressure was 2500 psi and I had about the same volume as an aluminium 80) and I have to say that having less weight is appreciated. Then again, I dive old gear, so no weight integrated stuff and those belts are just evil. If you have a weight integrated BC, it might not be as bad. In any case, steel is good with all that weight.
I dealt with the Monterey Bay Dive Company (
Welcome to Monterey Bay Dive Company) and they were really nice. Great service if you ask me. I'll go ahead and recommend them to you, although if you want to look around, I'm sure there are others. MBDC has a boat, the silver prince, which goes out on saturdays and sundays for a two tank trip. There are other boats in the area you can get onto, one I remember is the Cypress something (sorry, I didn't look very hard into these things, but I'm sure you can find the proper info online or someone else will add to this thread).
You're right, the water is in the 50s and it's not going to be florida water, but I'd say it's worth it. Maybe, being from Florida, you've seen it all before, but I thought the amount of life to see there was really impressive. If you're only going to dive for an afternoon, I would recommend you try to go to Point Lobos. It's only about 15-20 minutes away from Monterey and the site is quite amazing. If you want to go there on weekends, though, you'll have to reserve in advance. In fact, they may be booked for weekends over the summer already, one would have to check. During the week, you really only need to show up before 10:30 or 11:00 and you'll be able to go in. Point Lobos is a state reserve and they limit the number of divers to 15 teams of 2 or 3 divers each day.
I don't know how much experience you have, but point lobos has nice easy dives possible if you have someone taking you around the site. Otherwise, there's the breakwater, in Monterey. During the weekend, there will be quite a number of divers there doing classes.
Point Lobos and the breakwater are the only sites I went to, so I'm sure there's a number of sites I'm missing here. There were many people there who agreed with me that Point Lobos is a very, very nice dive site. There may be something more interesting than the breakwater, but I still found the breakwater an interesting site to dive.
By and large, I would say that dealing with the cold water is
a) not that bad (I'm biased, I certified in northern Quebec initially, so cold water is all I had, but I dove with a couple who'd only gone diving in Mexico before and they seemed quite happy and to have enjoyed themselves)
b) really worth it. There's a lot of life out there to see. The kelp is really interesting to look at and it just harbors a lot of life.
I recommend you do it. I'd recommend you do it more than an afternoon, but at the very least, go out and look at it. I don't think you'll regret it.