January is Winter, so it could be cold. Of course, this is SoCal, so it could also be 80*F. (I'd plan for cold, though) Plan for water temps in the low 50s. It being winter, of course, there can be no specific promises about conditions, but chances are decent it'll be good unless a storm comes through.
Lots of good shore diving with kelp in Malibu, farther to the North along the coast, but there's also kelp diving around Palos Verdes, which is close, but you'll need a boat to get there and it's not a regular charter destination (unless you charter a small boat just for you).
http://www.ecodivecenter.com/content/south...each-dive-sites
HB is right between two good diving areas. Laguna offers more protected conditions and easier diving, but it's not exactly a dense kelp forest. There's a decent amount of kelp at the Old Marineland site (see map above), but it's somewhat advanced, from an entry and exit standpoint, especially if you're not used to surf entries. It's a notorious site for pounding and injuring even those who dive it regularly, so make sure you hook up with a local.
Best guaranteed kelp diving from HB is either via boat or up North to Malibu (very easy shore diving, but a bit of a drive from HB).
Malibu and the Laguna sites both offer easy conditions and shallow dives, but Malibu has more kelp by far.
A boat to Catalina Island (the island you see offshore in the map) can offer great kelp diving as well, of course. Plenty of good boats that run out to Catalina regularly. Limited mid-week availability during the Winter, however, but lots of options on weekends.