Surf Forecasts:
Onjuku surf forecast from 20 Aug 2026:
- Best quality surf: Monday 24 Aug, 3AM (local time) - 3.5ft (1.1m), 18s period, SSE swell with cross-offshore winds.
- Most powerful swell: Tuesday 25 Aug, 9AM (local time) - 8ft (2.5m), 16s period, SSE swell with 3,114 kJ wave energy.
- Next surfable swell (1★+): Saturday 22 Aug, 9PM (local time) - 3.5ft (1.0m), 10s period with E swell.
Best Forecast Surf Conditions for Onjuku this week:
The surf forecast for Onjuku over the next 16 days: The first swell (rated 1 star or higher) is forecast to arrive on Saturday (Aug 22) at 9PM. The primary swell is predicted to be 1.0m and 10s period with a secondary swell of 0.5m and 5s. The wind is predicted to be cross-offshore as the swell arrives.
The most powerful waves expected at Onjuku in the next 16 days are 2.5m 16s and forecast to arrive on Tuesday (Aug 25) at 9AM. Winds are predicted to be onshore at the time the swell arrives. The largest open ocean swell (not directed at the beach) is 0.6m 4s period and expected on Sunday (Aug 23) at 12PM.
| Wave Type | Time (JST) & Date | Wave Height & Period |
|---|---|---|
| Next good surf (1 star+) | 9PM (Sat 22nd Aug) | 3.5ft (1.0m) 10s |
| Best Surf | 3AM (Mon 24th Aug) | 3.5ft (1.1m) 18s |
| Most Powerful | 9AM (Tue 25th Aug) | 8ft (2.5m) 16s |
Table - best surf conditions forecast for Onjuku over the next 16 days.
The Lowdown
Alright, mate, Rusty here. Let’s break it down.
The next few days are pretty flat, but there’s a massive pulse of energy building into the first week of September that could be something special if you’re experienced enough to handle it. The water temp is about average for this time of year, nothing unusual.
The first real surfable window doesn’t show up until Sunday the 23rd of August, and even then it’s only small and clean. Onjuku picks up a little 3ft swell from the east with a 10-second period on Sunday morning, winds are light and cross-off, so it’s tidy. The afternoon drops to 2ft from the SSE with a 12-second period, still clean. But honestly, it’s not much to get excited about – just a knees-and-ankles day.
Then Monday the 24th through to Wednesday the 26th of August, the swell starts to build but the wind is onshore, blowing onshore from the south or SSE, and the surf quality is poor. On Monday morning, there’s a 7ft swell from the SSE with a very long 17-second period – that’s real groundswell energy – and combined energy hits 2680, which is strong. But the onshore wind and the long period makes it tricky for a beach break like Onjuku. Tuesday morning sees 8ft from the SSE with a 16-second period, energy up to 3450, but still onshore wind. The conditions are marginal, and the size is getting into expert-only territory.
From Thursday the 27th of August all the way through to Saturday the 30th of August, it’s a mixed bag of rain, storms, and strong winds. The surf is poor, the swell drops off, and the winds are fresh and strong, mostly onshore or cross-onshore. Not worth paddling out for.
Sunday the 30th of August afternoon shows some promise – a 5ft swell from the SSE with a 16-second period, clean cross-off winds from the NE, and energy at 1472. Still moderate to strong, but clean. Things improve further on Monday the 31st of August and Tuesday the 1st of September, with 7ft to 8ft SSE and SE swells, long periods of 14 to 15 seconds, and clean cross-off winds. The morning of the 1st of September sees 8ft from the SE at 15 seconds, energy 2583. This is the best stretch of the early window – still big, but the wind is clean. It’s only for intermediate to expert surfers though.
Now, the real standout is the 2nd of September through to the 4th of September. This is a major, major swell event. On Wednesday the 2nd of September morning, Onjuku gets 10ft from the SE with a 16-second period, fresh offshore winds from the NNE, and combined energy of 5343 – that’s very strong. The afternoon jumps to 12ft from the SE, energy 7362, but the guidance says it’s too big for this break. By Thursday the 3rd, we’re talking 18ft to 21ft from the SSE with 17-second periods and energy readings of 17809 to 23121 – that’s enormous. The wind is strong offshore, so it’s clean, but only for absolute experts. Friday the 4th of September is the peak: 41ft from the SSE with an 18-second period, energy 93593, and strong offshore winds. It’s clean but ridiculously big – only for the brave and the very skilled. The afternoon drops to 28ft from the south, still huge.
If you’re a beginner, steer clear of the whole second week – it’s too big and too dangerous. For the experienced crew, the 2nd to the 4th of September is the big one, but remember, long-period swells like this can make beach breaks close out, so Onjuku might not be your best bet if that happens. It could be more interesting for the windsurf or kite crew when it’s that big.
The last day in the forecast, Saturday the 5th of September, drops back to 8ft from the SSE with a 10-second period, but the winds are still strong offshore, so it’s clean but short period.
Stay safe out there.
Rusty.
Short Range ForecastLight rain (total 9mm), mostly falling on Sat night. Warm (max 28°C on Sat morning, min 24°C on Sat night). Wind will be generally light. | Days 5-7 Weather SummaryModerate rain (total 18mm), heaviest on Wed morning. Warm (max 28°C on Tue morning, min 24°C on Sun night). Wind will be generally light. | ||||||||||||||||||
Friday 21 | Saturday 22 | Sunday 23 | Monday 24 | Tuesday 25 | Wednesday 26 | ||||||||||||||
Night | AM | PM | Night | AM | PM | Night | AM | PM | Night | AM | PM | Night | AM | PM | Night | AM | PM | Night | |
Swell Height Map | |||||||||||||||||||
Wave Height (m) Direction Period (s) | SE 11 | S 9 | S 8 | E 9 | E 11 | E 11 | E 10 | E 10 | SSE 12 | SSE 14 | SSE 17 | SSE 16 | SSE 15 | SSE 16 | S 14 | S 13 | S 13 | SSW 12 | SSE 9 |
Wave Graph | |||||||||||||||||||
40 | 40 | 92 | 41 | 151 | 233 | 198 | 113 | 104 | 379 | 2534 | 2588 | 2899 | 3114 | 2374 | 1329 | 764 | 250 | 238 | |
Wind (km/h) | |||||||||||||||||||
Wind State on-shore cross-onshore cross-shore cross-offshore off-shore glassy | on | cross-on | on | cross-on | cross-on | cross-on | off | cross-off | cross-off | cross-off | cross | on | on | on | on | on | on | on | on |
High Tide | 8:35PM1.27m | 9:35PM1.21m | 4:31PM1.15m | 11:58PM1.18m | 4:19PM1.20m | 1:32AM1.23m | 4:27PM1.25m | 2:31AM1.30m | 4:41PM1.29m | ||||||||||
Low Tide | 4:20AM0.49m | 6:00AM0.49m | 7:29AM0.43m | 7:50PM1.12m | 8:27AM0.35m | 8:48PM1.04m | 9:08AM0.28m | 9:22PM0.95m | 9:42AM0.22m | 9:51PM0.85m | |||||||||
— | 5:01 | — | — | 5:01 | — | — | 5:03 | — | — | 5:03 | — | — | 5:05 | — | — | 5:05 | — | — | |
6:22 | — | 6:21 | — | — | 6:19 | — | — | 6:17 | — | — | 6:16 | — | — | 6:15 | — | — | 6:14 | — | |
mm | — | — | — | 1 | — | 1 | 7 | — | — | — | 1 | — | — | — | — | 2 | 10 | 5 | 7 |
Temp °C | 26 | 27 | 27 | 26 | 28 | 27 | 25 | 26 | 26 | 25 | 27 | 27 | 26 | 28 | 28 | 27 | 25 | 27 | 27 |
Feels °C | 29 | 29 | 28 | 27 | 29 | 29 | 29 | 28 | 28 | 28 | 30 | 28 | 29 | 30 | 30 | 30 | 27 | 27 | 27 |
Swell 1 Height (m) Direction Period (s) | E 8 | E 8 | E 8 | E 9 | E 11 | E 11 | E 10 | E 10 | E 9 | SSE 14 | SSE 17 | SSE 16 | SSE 15 | SSE 16 | S 14 | S 13 | S 13 | SSE 9 | SSE 9 |
32 | 34 | 35 | 41 | 151 | 233 | 198 | 113 | 81 | 379 | 2534 | 2588 | 2899 | 3114 | 2374 | 1329 | 764 | 248 | 238 | |
Swell 2 Height (m) Direction Period (s) | SE 11 | S 9 | SE 10 | S 9 | SSW 9 | SSW 9 | S 5 | SSW 9 | SSE 12 | ENE 9 | E 12 | ESE 12 | E 14 | ESE 14 | ESE 13 | ESE 13 | SSE 10 | SSW 12 | E 12 |
40 | 39 | 39 | 38 | 28 | 27 | 10 | 15 | 104 | 82 | 132 | 186 | 206 | 198 | 184 | 176 | 208 | 250 | 70 | |
Swell 3 Height (m) Direction Period (s) | SSW 8 | SE 11 | SE 5 | SE 10 | SE 10 | SE 10 | SSW 9 | SE 13 | ESE 12 | SSE 20 | SSW 8 | SW 10 | E 11 | E 14 | SW 10 | SE 11 | ESE 12 | ESE 12 | SSW 11 |
13 | 40 | 1 | 36 | 25 | 28 | 26 | 45 | 56 | 336 | 14 | 36 | 114 | 138 | 15 | 58 | 117 | 113 | 64 | |
Wind waves Height (m) Direction Period (s) | SSE 5 | SSE 4 | S 8 | S 4 | S 5 | S 5 | — | NE 3 | NE 4 | — | — | SSW 8 | SW 10 | — | — | — | SSE 9 | — | — |
10 | 8 | 92 | 17 | 21 | 22 | — | 5 | 10 | — | — | 13 | 33 | — | — | — | 271 | — | — | |
Nearest Offshore or Glassy | |||||||||||||||||||
Distance (km) | 9 | 17 | 9 | 23 | 23 | 17 | 0 | 0 | 51 | 0 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 9 |
Best forecast wave conditions in Chiba | |||||||||||||||||||
Best forecast wave conditions in Japan | |||||||||||||||||||
Header Global | |||||||||||||||||||
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Information about the Onjuku Surf forecast
The above surf forecast table for Onjuku provides essential information for determining whether the surfing conditions will be good over the next 16 days. A general guide to surfing at Onjuku can be found by selecting the local surf guide option on the grey menu. Our Onjuku surf forecast is unique since it includes wave energy (power) that defines the real feel of the surf rather than just the height or the period. If you surf the same spot (Onjuku) regularly then make a mental note of the wave energy from the surf forecast table each time you go. Very soon you may start to choose your surf days based on the wave energy alone combined with our forecast of favourable offshore wind conditions. Our star ratings will help here and of course you will also find the usual wave height and period predictions on our surf forecasts as well as a full break down of the swell components under our advanced users option (to reveal that, click the little Einstein character under the tide times).
Further information to help with frequently asked questions about our surf forecast for Onjuku may be found under the help tab on the top menu and also by moving your mouse over the question marks on the surf forecast table itself. Please always bear in mind that the forecast is for near-shore open water and local factors at each surf break influence the actual breaking wave height, such as the beach / reef profile, water depths offshore and shelter.
Onjuku is 3 km (2 miles) from Ohara. If you plan a holiday in Chiba, look for hotels and other accommodation in Ohara. Ohara has rooms for a wide range of budgets as well as car hire and transport links.











