Conditions at Niijima in December
December: Winter Monsoon Returns
December closes the year with the biggest average swell height alongside January: 1.8m (6ft). The average period, however, drops to 7.2s, revealing the winter monsoon's signature short-period power. Directionally, W swell dominates at 29.9%, with WSW at 8.0% and WNW at 3.4%; the optimal east quadrant falls to 29.2%, led by ENE at 11.4% and E at 6.6%. The character shifts back to windswell generated by the Siberian high and strong westerly flow across the island chain.
Offshore winds are plentiful - W at 19.9%, WNW at 20.1%, NW at 4.5% - but these are the same winds that build the lumpy W windswell. Ideal surf wind clocks in at only 12%. To get quality, you need a low-pressure system south of Japan to inject genuine ENE groundswell into the mix; when that lines up with a lighter WNW offshore wind, Niijima can produce 6-8ft (1.8-2.4m) of grinding, powerful surf. Water temps are 20.0C, still surprisingly warm relative to air at 13.9C, and the dry winter signal is starting: rain drops to 2.82 mm/day. Winter rubber is required, and patience is a virtue.
Average Spot conditions at Niijima in December
Swell history for December
Wind history for December
Swell quality
Analyze the groundswell consistency at Niijima during December. Based on historical data, there is a % probability of groundswell occurring this month. The chart below provides a detailed breakdown of the average wave height distribution, offering deep insights into the swell quality and surf potential you can expect at Niijima for your next trip in December.
Ground swell
Ground swell by size
Wind conditions
Evaluate the wind and swell alignment at Niijima for December. Our analysis shows that favorable offshore or side-shore winds coincide with surfable swell approximately % of the time. The accompanying graph illustrates the average size distribution of waves during these optimal wind windows at Niijima.