Oniguchi - surf spot statistics

Best Surf Season (March - May)

As the Siberian high retreats and the Pacific storm track lifts north, spring delivers the most balanced combination of swell quality and wind reliability. The swell window from SSW to W becomes more active, with March seeing 13.1% of waves from these directions, April 16.1%, and May peaking at 19.0%. Meanwhile, offshore wind frequencies remain respectable—49% in March, 44% in April, and 43% in May—driven by lingering north and northeast flows. This is when consistent, fun-sized to good waves with clean faces are most likely, making March through May the prime window for surfers to plan a trip.

Fair Surf Season (June - August)

Summer is the reign of the Pacific typhoon, churning out abundant SSW to SW swell that directly hits Oniguchi’s SW exposure. June boasts a staggering 45.1% of swell from the optimal directions, July 54.5%, and August 32.0%—often delivering punchy, rideable to pumping sets. However, the trade-off is a dramatic rise in onshore southwest winds, with ideal wind percentages dropping to 34%, 21%, and 30% respectively. This is a high-risk, high-reward season: score a typhoon’s outer band combined with a brief high-pressure ridge, and you’ll find epic, glassy waves. More often, though, you’ll be battling cross-shore chop. Patience and a keen eye on local pressure patterns are key.

Low Surf Season (September - February)

From late summer through early winter, the balance shifts away from quality surf. September sees a sharp decline in optimal swell (13.8%) despite improving wind (53% ideal). October and November are dominated by east and northeast swell (44.8% combined in October, 37.1% in November), which hits Oniguchi with poor direction and often short period, while offshore winds peak (68% and 66% ideal) but go largely wasted. December, January, and February bring the region’s largest NW swell (32.8%, 39.5%, 31.2% respectively), but these waves rarely wrap into Oniguchi’s SW-facing beach; the optimal swell window shrinks to under 5% in each month. While offshore winds remain frequent (54-60%), the lack of suitable swell direction means most days are small, messy, or just plain flat. Occasionally, a rogue storm in the Sea of Japan can fire up a SW pulse, but these are isolated exceptions during this low season.

August: Transitioning Swell, Slightly Better Wind Odds

August continues the summer pattern but with a slight drop in optimal swell (32.0%) and a modest uptick in ideal wind (30%). Swell from SW (11.0%) and SSW (8.8%) still dominates, but the average period rises to 8.2s, making waves more powerful. Wind roses show a shift: onshore southwest wind remains (SW 7.1%, WSW 7.0%), but offshore directions from E (10.6%) and ENE (7.0%) become more frequent, offering more rideable days. The typhoon track typically shifts closer to Japan, which can bring both swell and unfavorable wind. The best setup is a late-season typhoon that spins north of Taiwan, sending clean SW groundswell while a northeast monsoon flows out of the Sea of Japan. August edges closer to the sweet spot between swell quality and wind reliability, making it a fair month for those willing to gamble.