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.

July: Peak Typhoon Swell – Epic Potential, Frequent Onshores

July is the zenith of the typhoon season, with a massive 54.5% of swell arriving from the SSW to WSW window. SW swell alone makes up 23.8%, and waves frequently push into the 1.5-2.5m pumping range. The average period increases to 7.6s, adding power. However, onshore wind conditions dominate: ideal wind is only 21%, with SW (14.2%), WSW (12.4%), and SSW (10.7%) ruining many sessions. The swell is there, but the wind is often cruel. When a tropical cyclone recurves far enough south and stalls over the East China Sea, it can generate prolonged SW swell while a strong high-pressure system over the Sea of Japan brings offshore NE flow. Those are the legendary days—glass faces, long-period lines, and tubes at Oniguchi. But patience is tested: you may wait a week for one perfect day. July is for the risk-takers who live for the score.