Sea conditions in Cyprus are generally excellent throughout the year and you can have perfect conditions for diving during any month.
Obviously conditions in the summer months tend to be generally calmer, warmer and have better visibility, with the winter months then being more unpredictable.
From about the middle to end of November the weather continues to be warm but with temperatures cooling and more chances of rain the sea conditions start to change. Temperatures start to drop and there is more wind and stormier weather but the climate can still be excellent right up until the end of the year. We have a lot of diving in November and December but as mentioned conditions are more unpredictable.
January to March sees the main winter type of sea and land conditions in Cyprus. The water is at its coldest but still a good 16-17degC and the sea is rougher and more prone to storms and big seas. Again though you have regular spells of lovely weather and good sea conditions for diving. We have had regular spells of 30 metres visibility during these months.
As you then move into April and May things start to warm up and sea conditions generally improve. As always with the sea you can still get bad conditions for diving but by the end of May sea temperatures are up into the twenties.
June, July and August see the start of the main summer heat starting to increase to it's highest levels in August. The sea is now continuing to warm, visibility is very good and the sea is generally calm but you can still get blown out. September and October are great months for diving as are the first few weeks in November. Air temperatures have dropped to perfect levels and are still nice and warm, the sea is at it's calmest and warmest with visibility up to 40 metres plus ! The sea temperature can be up to 30degC by the end of August and remain at 27degC + throughout September and October. By the start of November you are looking at about 25degC and by the end 22 if weather conditions remain good throughout.
Then as we get to the end of November and into December the sea conditions are still generally good but you will get the odd rainy day or some more blustery conditions. Some years though we have no rain until January and the diving continues to be excellent. Sea temperatures by now are heading towards about 20degC and visibility still tends to be very good.
So in general you can dive all year round but with more of an eye on the forecast during the winter months and especially January to March when there is a lot less diving, but as mentioned you can still get great spells for diving during these months too.