Surf Forecasts:
Onjuku surf forecast from 18 Aug 2026:
- Best quality surf: Tuesday 25 Aug, 9AM (local time) - 3.5ft (1.0m), 12s period, SSE swell with cross-offshore winds.
- Most powerful swell: Tuesday 25 Aug, 6PM (local time) - 5ft (1.6m), 13s period, SSE swell with 775 kJ wave energy.
- Next surfable swell (1★+): Wednesday 19 Aug, 3AM (local time) - 2ft (0.6m), 8s 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 Wednesday (Aug 19) at 3AM. The primary swell is predicted to be 0.6m and 8s period with a secondary swell of 0.6m and 6s. The wind is predicted to be glassy as the swell arrives.
The most powerful waves expected at Onjuku in the next 16 days are 1.6m 13s and forecast to arrive on Tuesday (Aug 25) at 6PM. Winds are predicted to be cross-shore at the time the swell arrives. The largest open ocean swell (not directed at the beach) is 0.5m 3s period and expected on Sunday (Aug 23) at 3AM.
| Wave Type | Time (JST) & Date | Wave Height & Period |
|---|---|---|
| Next good surf (1 star+) | 3AM (Wed 19th Aug) | 2ft (0.6m) 8s |
| Best Surf | 9AM (Tue 25th Aug) | 3.5ft (1.0m) 12s |
| Most Powerful | 6PM (Tue 25th Aug) | 5ft (1.6m) 13s |
Table - best surf conditions forecast for Onjuku over the next 16 days.
The Lowdown
Alright, let’s talk about Onjuku in feet and miles per hour. For the first week, it’s a total write-off. From Tuesday the 18th through Sunday the 23rd, we’re looking at tiny, gutless waves—most of the time under 3 feet—with constant onshore or cross-shore wind. The wave energy is weak, barely registering. There’s a brief moment on Sunday morning the 23rd when the wind goes glassy, but the swell is still only about 3 feet and inconsistent. It’s a quick paddle, not a session.
The action starts Tuesday the 25th of August. That morning, we get a clean 3-foot swell from the SSE, with a 12-second period and light offshore wind from the ENE. The energy is moderate at 729. This is the first real window. By the afternoon, the swell picks up to 5 feet, still SSE, with a 13-second period, but the wind turns cross-shore and a bit lumpy. It’s okay, but not perfect.
Wednesday the 26th, the swell is 6 feet from the SSE, with a 14-second period. The energy is strong at 1324. The wind is cross-shore, so it’s a bit lumpy. That’s a solid groundswell—plenty of power, but the long period might make it a bit straight at the beach break. It’s for the better surfers.
The best call is Friday the 28th of August. The morning has 6-7 feet of south swell, 14-second period, with a strong offshore wind from the NE at 28 mph. That’s clean, powerful, and heavy. The energy is 1754. It’s going to be a serious paddle, but the waves will be well-shaped and hollow. The afternoon gets a gale-force offshore wind at 43 mph, making it nearly impossible to paddle out.
Into the next week, Monday the 1st of September, the swell is 8-10 feet from the east, but the wind is screaming onshore at 28-31 mph. This is a disaster for surfing—just blown-out, dangerous, and ugly. More of a kite session.
Then Wednesday the 2nd of September, the models show a massive 16-21 foot east swell, with a 15-second period, and strong offshore wind. The energy is astronomical— 6979 to 16655. That’s a monster swell, way too big for Onjuku. Only for the absolute elite, and even then, it’s a survival mission.
For the everyday surfer, the Tuesday 25th morning is your best bet: clean, 3-foot waves, and not too crowded. For the experts, the Friday 28th morning is the standout—big, powerful, and clean. Stay away from the rest.
The water is about 80°F, which is normal for this time of year.
Rusty.
Short Range ForecastMostly dry. Warm (max 27°C on Tue afternoon, min 25°C on Tue night). Wind will be generally light. | Days 5-7 Weather SummaryModerate rain (total 19mm), heaviest on Sat morning. Warm (max 28°C on Sat morning, min 25°C on Sat night). Wind will be generally light. | |||||||||||||||||||
Tue 18 | Wednesday 19 | Thursday 20 | Friday 21 | Saturday 22 | Sunday 23 | Monday 24 | ||||||||||||||
PM | 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) | E 8 | E 8 | E 8 | E 9 | E 9 | SE 10 | SE 11 | SE 11 | ESE 8 | SE 10 | E 9 | E 11 | E 10 | E 10 | E 10 | E 10 | E 9 | E 12 | E 12 | ESE 11 |
Wave Graph  | ||||||||||||||||||||
 kJ | 61 | 47 | 50 | 36 | 37 | 39 | 40 | 40 | 53 | 39 | 57 | 149 | 204 | 158 | 154 | 117 | 79 | 70 | 71 | 68 |
Wind (km/h) | ||||||||||||||||||||
Wind State on-shore cross-onshore cross-shore cross-offshore off-shore glassy | cross-on | cross-on | cross-off | cross-on | cross-on | cross-on | on | on | on | on | cross-on | cross-on | cross-on | cross-on | glassy | cross-on | cross-on | on | on | cross-on |
High Tide | 7:22PM1.39m | 8:37AM1.06m | 7:42PM1.36m | 9:58AM0.96m | 8:05PM1.32m | 8:35PM1.27m | 9:35PM1.21m | 4:31PM1.15m | 11:58PM1.18m | 4:19PM1.20m | 1:32AM1.23m | |||||||||
Low Tide | 2:17AM0.43m | 1:24PM0.80m | 3:09AM0.46m | 1:21PM0.89m | 4:20AM0.49m | 6:00AM0.49m | 7:29AM0.43m | 7:50PM1.12m | 8:27AM0.35m | 8:48PM1.04m | ||||||||||
 |  |  | | | | |  | | |  |  | |  | | | | | | | |
 | — | — | 5:00 | — | — | 5:01 | — | — | 5:01 | — | — | 5:01 | — | — | 5:03 | — | — | 5:03 | — | — |
 | 6:23 | — | — | 6:22 | — | — | 6:22 | — | — | 6:21 | — | — | 6:19 | — | — | 6:17 | — | — | 6:16 | — |
mm | — | — | — | — | — | — | — | — | — | — | 1 | 3 | 3 | 5 | 3 | 3 | 1 | — | — | — |
Temp °C | 27 | 26 | 27 | 27 | 26 | 27 | 27 | 26 | 27 | 27 | 26 | 28 | 28 | 26 | 26 | 27 | 26 | 27 | 27 | 26 |
Feels °C | 29 | 29 | 29 | 29 | 29 | 29 | 29 | 29 | 30 | 28 | 29 | 30 | 30 | 30 | 31 | 31 | 29 | 29 | 28 | 30 |
Swell 1 Height (m) Direction Period (s) | E 8 | SE 6 | SE 6 | E 9 | SE 6 | SE 6 | SE 5 | E 8 | ESE 8 | E 8 | SSE 5 | E 11 | E 10 | E 10 | E 10 | E 10 | E 9 | E 9 | E 9 | ESE 11 |
| kJ | 61 | 31 | 23 | 36 | 25 | 25 | 14 | 32 | 53 | 35 | 13 | 149 | 204 | 158 | 154 | 117 | 79 | 57 | 55 | 68 |
Swell 2 Height (m) Direction Period (s) | SE 10 | E 8 | E 8 | SE 10 | E 9 | E 8 | E 8 | SE 11 | S 9 | S 8 | E 9 | S 5 | S 5 | S 5 | SSW 9 | SSW 9 | E 12 | E 12 | E 12 | E 8 |
| kJ | 37 | 47 | 50 | 35 | 37 | 33 | 33 | 40 | 39 | 36 | 57 | 27 | 26 | 12 | 28 | 27 | 72 | 70 | 71 | 34 |
Swell 3 Height (m) Direction Period (s) | SSW 8 | SE 10 | SE 10 | SSW 8 | SE 10 | SE 10 | SE 11 | SE 5 | SE 11 | SE 10 | SE 10 | S 10 | SSW 9 | SSW 9 | SE 11 | SE 11 | SSW 9 | SE 10 | SSE 9 | SSE 11 |
| kJ | 6 | 36 | 35 | 6 | 35 | 39 | 40 | 10 | 40 | 39 | 50 | 48 | 28 | 29 | 29 | 29 | 26 | 24 | 34 | 45 |
Wind waves Height (m) Direction Period (s) | SE 7 | — | — | SE 6 | — | — | — | SSE 5 | — | S 3 | — | S 5 | SSW 5 | NE 3 | ENE 4 | ENE 4 | — | — | — | — |
| kJ | 21 | — | — | 21 | — | — | — | 11 | — | 2 | — | 43 | 36 | 3 | 5 | 2 | — | — | — | — |
Nearest Offshore or Glassy | ||||||||||||||||||||
Distance (km) | 9 | 9 | 0 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 17 | 9 | 9 | 9 | 0 | 9 | 9 | 9 | 9 | 9 |
Best forecast wave conditions in Chiba | ||||||||||||||||||||
Best forecast wave conditions in Japan | ||||||||||||||||||||
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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.
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