Through the two oceans meeting each other, the climate is diverse. Most of the province has a Mediterranean climate with cool, wet winters and warm, dry summers. Other parts have a maritime climate with cool, moist winters and mild, moist summers. In the Karoo area there’s a semi-arid climate with cold, frosty winters and hot summers with occasional thunderstorms.
The water temperature is different at The Atlantic Coast and False Bay. The Atlantic Coast is colder, this is because the Benguela currents. Water temperatures are between 10°C and 12°C year-around. The best time for diving is in the summer (October to February). Visibility is between 10 and 20 meter. If you dive with a north-western wind you can have a visibility less than 2 meters. Dry suits are advised. Watch out for strong currents and reefs.
False Bay is a lot milder, because it’s protected from winds and currents through the Cape Peninsula. Winter is probably the best time to dive (March to September), but it’s hard to be sure because of the fast changing weather there. Visibilities can catch up to 15 meters after a period of north-westerly winds. Water temperatures are between 12°C and 18°C.
If you want to go shark cage-diving, best time to do is in the months April to October. Tiger shark diving can be best done during summer (October to February).