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.

March: Spring Awakening with Balanced Swell and Wind

March marks the beginning of the best surf season. The average swell height eases to 1.2m, but the period lengthens slightly to 7.1s. Optimal swell from SSW-SW-WSW-W now accounts for 13.1% of total—up from February—with more waves in the 1-1.5m fun range. The dominant swell is still NW (18.5%) and E (9.5%), but the increasing presence of W and SW pulses is encouraging. Offshore wind frequencies remain decent at 49%, with strong contributions from N (7.7%), NNE (4.1%), and a favorable ENE (7.0%) flow. As the Aleutian low weakens and the Pacific high begins to strengthen, we see a more winnowed window with cleaner conditions. Look for days when a low-pressure trough swings through the Sea of Japan, generating SW swell under a crisp north to northeast breeze—those are the gems of March.