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.

December: Winter Swell Peaks, Wind Holds – Low-Quality Combo

December brings the largest average swell heights of the year at 1.3m, with a period of 7.6s. The swell direction is overwhelmingly from the northwest (32.8%) and north-northwest (13.9%), directions that typically bypass Oniguchi. Optimal SW-W swell drops to just 4.8%. Fortunately, offshore wind remains strong at 60%, with N (18.6%) and NNW (29.9%) blowing crisp and clean. This creates a frustrating mismatch: plenty of offshore wind but the wrong swell. On rare occasions, when a strong low moves south of Honshu and sets up a long-fetch SW path, we can see powerful, clean lines. But most of the time December offers small, bumpy waves from the east or large, unmanageable NW swell. The wind is your friend, but the swell is not. Unless you’re praying for a storm diversion, December is a low-surf month at Oniguchi.