I'm not sure if I would term it a "migration," but February-March-April seems to be when we see the most great hammerheads at our feed sites off Jupiter. They are sighted at other times of the year, but that seems to be when we have a reasonable chance of going down and getting 3-6 over the course of a 3-tank dive trip. Conventional wisdom is that the hammerheads are there to feed on the mass blacktip shark migration inshore. When spring rolls around it gets close to turtle season, which also brings in the tigers. Going a little farther offshore into 120-150 fsw you'll run into large numbers of bull sharks, and through February we typically still have the out-of-town lemon sharks (there are local residents year-round, but we have some identifiable ones that only turn up in winter).
A couple things to remember is that the dive conditions are going to be very different than the Bahamas; you're in 65-140 fsw (on the deep ledge you typically level out at 90-100 and don't go all the way to the bottom), it's drift diving/live boat drops in what can be a strong current (3-4 knots at the high end), and overall you're expected to be more self-reliant as a diver (these dives are one reason I started carrying a pony bottle). Richard has an excellent writeup on a trip he did last April here:
Emerald Dive Charters Trip Report
The other note is that in Jupiter/West Palm the dive charter options are more limited - last year we had three SCUBA charters out baiting for sharks;
Deep Obsession has since changed ownership and no longer does baited shark dives that I'm aware of. That leaves
Emerald and
Miss Jackie (the latter run as Calypso Dive Charters); between the two of them that's 20 seats. Baited dives for sharks is a very loaded topic in FL (it's illegal inside state waters, so the fun and games have to stay outside the 3-mile limit); a lot of charters in the Palm Beach and Martin County will try to see sharks without bait. Your mileage may vary on this; you should have no problems seeing lemon and reef sharks that way but tigers and hammerheads will likely be lottery odds. The other area that has been growing is baited surface snorkel trips; these are actually as or more expensive than the SCUBA charters but the upside is sold as having no "bottom time" limits.