Conditions at Niijima in September
September: The Peak of the East-Swell Window
September is the most consistently interesting month on the east-facing Niijima calendar. Swell height averages 1.6m (5ft), period is 8.7s, and the optimal NE-SE quadrant commands 55.3% of the directional spectrum. E leads at 15.9%, ENE follows at 13.2%, ESE at 13.4%, and SE at 10.3%. This is the climatological apex of typhoon-generated groundswell in the region, and the tropical Pacific is still warm enough to send powerful, organized swell trains toward the Izu Islands.
The catch is wind. North and northeast onshores become stronger: NE at 19.6%, ENE at 14.4%, giving that quadrant 34.0% - the highest of the year. Offshore WSW and SW total 19.8%. Ideal wind drops to 15%, so you have to pick your windows carefully. The specialty setup is a typhoon tracking east of Japan, generating E/ENE groundswell while a cold front sweeps down and clocks the wind to W/NW: that combination produces 4-6ft (1.2-1.8m) or bigger, lined-up surf. With water at 26.6C and air at 25.2C, it is tropical storm-chasing at its finest. Rain is heavy at 7.94 mm/day.
Average Spot conditions at Niijima in September
Swell history for September
Wind history for September
Swell quality
Analyze the groundswell consistency at Niijima during September. 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 September.
Ground swell
Ground swell by size
Wind conditions
Evaluate the wind and swell alignment at Niijima for September. 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.