December is the beginning of the windy and dry season. The "dry" won´t affect the diving, but the "windy" can make the sea somewhat rougher, especially on the off-shore Islands like Cats and Bats (the Islands give shelter, but the boat ride to get there is exposed). The wind usually starts in the early after-noon and lets you enjoy the morning dive excursion in calm conditions. You will find similar conditions all around the Gulf of Papagayo: The Cats, the Bats and what we call the "local" dive sites (10 to 20min away by boat). With the wind having started (there is no exact date yet, it could also be in January only), the water temperature is likely to drop a few degrees to around 23 to 25 C or low to upper 70´s F and below the common thermoclines at a depth of around 15 to 20m / 45 to 60 ft the temperature is a bit less from 20 to 23 C or around 70 F, at some occasions it can get less. If you plan to dive several days and bring along your own gear, take a 5mm suit. The common rental suits in the area are 3mm which might be a bit chilling at that time of the year (well, you can ask for 2 suits...:-D).
Visibility can also be affected by the wind. Don´t overestimate this factor there is always a lot to see; instead of worrying where the rock ends, just enjoy what´s around you! What lowers the viz are sediments that swell up to the coast because of the wind where tons of marine life feeds on it. Expect 10 to 30ft and you won´t be disappointed.
O.K. "be prepared for worst-case scenario", "use apropriate exposure protection" and "have positive attitude" for better enjoyment are some tips for diving the Gulf of Papagayo and anywhere else...:-D!
