When Is Kerama Water Temperature Best? A Data-Driven Seasonal Guide

The Kerama Islands are located about 50 minutes by fast ferry from Naha, Okinawa. Known worldwide for their "Kerama Blue" crystal-clear waters, these islands were designated a National Park in 2014. With approximately 250 coral species, Kerama boasts some of the highest marine biodiversity in the world.

Our database contains 1,533 days of water temperature and visibility records for Kerama. While the islands enjoy warm water year-round, this analysis identifies exactly when conditions are optimal for diving.

Monthly Temperature Trends

Compare Kerama with Ishigaki and Kushimoto. Despite all three being influenced by warm currents, latitude makes a clear difference.

Seasonal Diving Guide

Winter: Jan-Mar (21.2-21.7°C)

Kerama's winter is remarkably warm by mainland Japanese standards. Even in February, the coldest month, the average temperature is 21.2°C — warm enough for a 5mm wetsuit. Add a hood vest or thermal inner for extra comfort. Winter brings strong northerly winds that can make sea conditions unpredictable, but calm days reward divers with pristine Kerama Blue visibility.

A unique winter highlight is humpback whale watching. From January to March, these majestic creatures visit Kerama waters to breed and nurse their calves, offering spectacular sightings from dive boats. Fewer tourists also mean popular sites are nearly private.

Spring: Apr-May (22.5-23.8°C)

Temperatures climb gradually to 22.5°C in April and 23.8°C in May. A 5mm wetsuit is perfectly comfortable. Golden Week (late April to early May) is one of the best times to visit in terms of both water temperature and weather. April marks the end of humpback whale season, after which the underwater world grows calmer. Spring offers stable visibility, suitable for all experience levels.

Summer: Jun-Aug (26.0-28.3°C)

Summer brings temperatures of 26.0°C in June, 27.5°C in July, and 28.3°C in August. A 3mm wetsuit or even a rash guard is sufficient — cold is simply not a concern. After the rainy season ends, July and August bring stable weather and peak sea surface temperatures. Coral spawning can be observed in May-June. Be aware that typhoon season overlaps, so schedule flexibility is important.

Autumn: Sep-Nov (24.2-27.8°C)

September holds at 27.8°C, October at 26.2°C, and November is still 24.2°C. Autumn may be Kerama's best-kept secret. Summer crowds thin out, typhoon risk drops, yet water remains genuinely warm. A 5mm wetsuit is comfortable, visibility is excellent, and dive sites are less crowded. For the savvy diver, this is arguably the optimal time to visit.

Early Winter: December (23.2°C)

December averages 23.2°C, still comfortable in a 5mm wetsuit. Kerama is a popular destination for year-end diving holidays. While mainland Japan shivers, divers here enjoy subtropical water temperatures through Christmas and into the New Year.

Comparison with Ishigaki and Kushimoto

The chart shows that Kerama and Ishigaki follow nearly identical temperature curves. Both stay above 21°C year-round, reaching about 28°C in summer — a huge advantage for wetsuit-only divers. In contrast, Kushimoto on the southern tip of Honshu drops to 16-17°C in winter, requiring a drysuit. Kerama is roughly 5°C warmer than Kushimoto in winter, a difference driven by proximity to the main Kuroshio Current.

Suit Recommendations