Surf Forecasts:
Onjuku surf forecast from 15 Aug 2026:
- Best quality surf: Sunday 16 Aug, 6AM (local time) - 4.5ft (1.4m), 10s period, E swell with cross-offshore winds.
- Most powerful swell: Sunday 16 Aug, 6AM (local time) - 4.5ft (1.4m), 10s period, E swell with 362 kJ wave energy.
- Next surfable swell (1★+): Sunday 16 Aug, 3AM (local time) - 4ft (1.2m), 10s period with ESE 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 Sunday (Aug 16) at 3AM. The primary swell is predicted to be 1.2m and 10s period with a secondary swell of 0.5m and 9s. 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 1.4m 10s and forecast to arrive on Sunday (Aug 16) at 6AM. Winds are predicted to be cross-offshore at the time the swell arrives. The largest open ocean swell (not directed at the beach) is 0.3m 2s period and expected on Wednesday (Aug 19) at 9AM.
| Wave Type | Time (JST) & Date | Wave Height & Period |
|---|---|---|
| Next good surf (1 star+) | 3AM (Sun 16th Aug) | 4ft (1.2m) 10s |
| Best Surf | 6AM (Sun 16th Aug) | 4.5ft (1.4m) 10s |
| Most Powerful | 6AM (Sun 16th Aug) | 4.5ft (1.4m) 10s |
Table - best surf conditions forecast for Onjuku over the next 16 days.
The Lowdown
G’day, Rusty here. Look, I’m gonna level with you straight up: Onjuku’s 16-day outlook is a bit of a mixed bag, with a lot of waiting around for the real juice, and even then it comes with some serious caveats. The first solid surfable window doesn’t appear until Monday morning, August 17th.
Let’s start with that Monday. On the morning of the 17th, we’ve got a little 3ft easterly swell pushing in with a 9-second period, and the wind is a clean cross-off from the ENE at 15 km/h. The wave energy is pretty weak (207), so it’s small, but the conditions are clean. It’s a nothing-special but fun little session for an intermediate. That same clean setup carries through the afternoon, with the swell dropping to 3ft but the period shortening to 8 seconds. Crowds are possible here, so don’t expect it empty.
The next few days are pretty grim. Tuesday the 18th and Wednesday the 19th offer tiny, weak swells (2ft) with messy cross-shore winds and poor surf conditions. On Wednesday morning there’s a brief window of clean cross-off wind and 2ft SE swell, but it’s honestly just ordinary. Thursday the 20th and Friday the 21st are a write-off – poor surf, light onshore winds, and small, weak energy (around 156–245). Saturday the 22nd is all onshore wind and poor surf, not worth a paddle.
Now here’s where it gets interesting but also a bit risky. On Sunday, August 23rd, a big pulse of ESE swell hits, jumping to 12ft in the morning and 10ft in the afternoon, with a short 8-second period. That’s a lot of water moving, with strong wave energy (1527–2240), but the wind is a moderate cross-onshore from the SSW at 20–25 km/h, making it choppy and poor. The size is already over 8ft, so this is for experienced surfers only, and honestly, with that wind, it looks more like a kite-surfing session than a clean paddle session.
The real standout, and I mean the *only* true standout in this whole forecast, is Tuesday, August 25th. On the morning, we’ve got a solid 7ft SSE groundswell, with a very long 15-second period, and the wind is light onshore from the south at only 5 km/h. The wave energy is pumping (2741), and while the report says “marginal” conditions, that long period combined with near-calm wind means there will be clean, powerful lines. This is a groundswell, so it’s best suited for a point break or reef – Onjuku is a beach break, so watch out for those sets breaking a bit too straight. Still, this is the best on offer. The afternoon sees the swell bump to 10ft with the same long period, but the wind swings to a gentle cross-onshore (15 km/h), making it a bit choppy. Still, that morning session is the one.
Wednesday the 26th is too big and stormy, with a risk of thunderstorms and 8ft SSE swell, but the wind goes clean cross-off in the afternoon (ENE 20 km/h), so for the brave, there might be a few clean ones. But the energy is massive (2841), and it’s still very big for the break.
Thursday the 27th is a no-go for paddling. We’re talking 10–12ft SSE swell with a gale-force NE wind at 65–80 km/h, producing insane wave energy (4002–5446). That’s a hard pass.
Friday the 28th stays huge (13ft) with onshore wind – poor and dangerous.
Now, Saturday the 29th is a tease. The swell is still 12ft SE, but the wind is a clean cross-off from the NNE at 25 km/h. The report says the swell is too big for the break, and I agree. That’s expert-only, and even then, it’s a risk.
The last few days, Sunday the 30th and Monday the 31st, see the swell dropping back to 7ft and 6ft with cleaner cross-off winds, but the energy is still moderate (850–637). Monday the 31st has a 15ft E swell with a 13-second period and a fresh offshore from the north at 35 km/h, but again, it’s too big for this spot.
Water temp is about average for the time of year, nothing unusual.
So, bottom line: the best session is Tuesday morning, August 25th. That’s the one to circle. Everything else is either too small, too messy, or too big. The long-range stuff (second week) is promising in size but comes with major wind and size issues. Stay safe out there.
Rusty.
Short Range ForecastLight rain (total 4mm), mostly falling on Sat night. Warm (max 27°C on Tue morning, min 24°C on Sat night). Wind will be generally light. | Days 5-7 Weather SummaryMostly dry. Warm (max 27°C on Wed morning, min 24°C on Tue night). Wind will be generally light. | ||||||||||||||||||
Sunday 16 | Monday 17 | Tuesday 18 | Wednesday 19 | Thursday 20 | Friday 21 | ||||||||||||||
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) | ESE 9 | E 9 | E 8 | E 9 | E 9 | E 8 | E 8 | E 8 | SE 8 | SE 8 | SE 8 | ESE 7 | E 8 | E 8 | E 8 | E 8 | ESE 8 | S 11 | S 10 |
Wave Graph | |||||||||||||||||||
308 | 256 | 195 | 230 | 154 | 147 | 136 | 57 | 69 | 60 | 60 | 72 | 95 | 147 | 144 | 127 | 96 | 116 | 130 | |
Wind (km/h) | |||||||||||||||||||
Wind State on-shore cross-onshore cross-shore cross-offshore off-shore glassy | cross-off | cross | cross | cross-off | cross-off | cross-off | cross | cross | cross | cross-on | cross-off | cross | cross-on | cross | cross-on | on | cross-on | cross-on | on |
High Tide | 6:12AM1.40m | 6:43PM1.39m | 6:57AM1.29m | 7:02PM1.40m | 7:43AM1.18m | 7:22PM1.39m | 8:37AM1.06m | 7:42PM1.36m | 9:58AM0.96m | 8:05PM1.32m | 8:35PM1.27m | ||||||||
Low Tide | 00:15AM0.53m | 12:27PM0.38m | 00:54AM0.46m | 12:51PM0.53m | 1:34AM0.43m | 1:11PM0.67m | 2:17AM0.43m | 1:24PM0.80m | 3:09AM0.46m | 1:21PM0.89m | 4:20AM0.49m | ||||||||
— | 4:58 | — | — | 4:58 | — | — | 4:58 | — | — | 5:00 | — | — | 5:01 | — | — | 5:01 | — | — | |
6:28 | — | 6:27 | — | — | 6:25 | — | — | 6:23 | — | — | 6:22 | — | — | 6:22 | — | — | 6:21 | — | |
mm | 1 | 2 | — | — | — | — | 1 | — | — | — | — | — | — | — | — | — | — | — | — |
Temp °C | 24 | 26 | 26 | 24 | 26 | 26 | 25 | 27 | 27 | 25 | 27 | 27 | 25 | 27 | 27 | 25 | 27 | 27 | 25 |
Feels °C | 25 | 27 | 27 | 25 | 27 | 28 | 28 | 29 | 29 | 28 | 29 | 29 | 28 | 29 | 29 | 28 | 29 | 29 | 28 |
Swell 1 Height (m) Direction Period (s) | ESE 9 | E 9 | S 9 | E 9 | E 9 | E 8 | E 8 | E 8 | SE 8 | SE 8 | SE 8 | ESE 7 | E 8 | E 8 | E 8 | E 8 | ESE 8 | ESE 7 | E 8 |
308 | 256 | 36 | 230 | 154 | 147 | 136 | 57 | 65 | 60 | 60 | 69 | 95 | 147 | 144 | 127 | 96 | 91 | 78 | |
Swell 2 Height (m) Direction Period (s) | S 9 | SSW 9 | ESE 9 | S 9 | S 8 | SSW 8 | SE 10 | SE 8 | E 8 | E 9 | E 8 | E 9 | SE 10 | SE 10 | SE 11 | S 8 | SE 10 | S 11 | S 10 |
41 | 27 | 35 | 23 | 23 | 23 | 38 | 42 | 69 | 56 | 48 | 23 | 35 | 28 | 42 | 22 | 39 | 116 | 130 | |
Swell 3 Height (m) Direction Period (s) | SE 10 | ESE 9 | SE 11 | SE 11 | SE 11 | SE 11 | SSW 8 | SE 10 | SE 10 | SE 10 | SE 10 | SE 10 | SSW 8 | SSW 8 | S 10 | SE 11 | S 8 | SE 10 | SE 11 |
27 | 32 | 32 | 31 | 30 | 30 | 13 | 36 | 27 | 27 | 35 | 35 | 7 | 7 | 7 | 40 | 21 | 38 | 42 | |
Wind waves Height (m) Direction Period (s) | — | — | E 8 | — | — | — | — | — | — | — | NE 2 | ENE 8 | ESE 7 | — | — | — | — | — | — |
— | — | 195 | — | — | — | — | — | — | — | 1 | 72 | 56 | — | — | — | — | — | — | |
Nearest Offshore or Glassy | |||||||||||||||||||
Distance (km) | 0 | 56 | 103 | 0 | 0 | 0 | 17 | 56 | 9 | 9 | 0 | 17 | 9 | 17 | 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.











