Awesome dives await off the coast of Sao Tome. The pinnacles of Pedra and Dahlo are excellent places to see huge barracuda. The two formations poke above the surface, stretching to meet the sun. You can see octopi in the cracks, as well as a variety of eels. Down at the bottom, nurse sharks relax, waiting for night to fall.
Head to Bone de Jockey, a stellar site that dons a humungous boulder. There are several sites around the huge rock, all of which give great views. There are massive grouper to be found here, sometimes surprisingly massive.
Diving in Sao Tome is pleasant all year but the visibility on the islands is clearest from December to March, and you can expect lovely warm water during this time.