Surf Forecasts:
Avellanas Rivermouth surf forecast from 21 Aug 2026:
- Best quality surf: Friday 28 Aug, 9AM (local time) - 2.5ft (0.8m), 19s period, SW swell with glassy winds.
- Most powerful swell: Friday 28 Aug, 6PM (local time) - 3.5ft (1.1m), 18s period, SW swell with 694 kJ wave energy.
- Next surfable swell (1★+): Monday 24 Aug, 3PM (local time) - 2.5ft (0.7m), 17s period with SW swell.
Best Forecast Surf Conditions for Avellanas Rivermouth this week:
The surf forecast for Avellanas Rivermouth over the next 16 days: The first swell (rated 1 star or higher) is forecast to arrive on Monday (Aug 24) at 3PM. The primary swell is predicted to be 0.7m and 17s period with a secondary swell of 0.8m and 9s. The wind is predicted to be glassy as the swell arrives.
The most powerful waves expected at Avellanas Rivermouth in the next 16 days are 1.1m 18s and forecast to arrive on Friday (Aug 28) at 6PM. Winds are predicted to be glassy at the time the swell arrives. The largest open ocean swell (not directed at the beach) is 0.6m 5s period and expected on Saturday (Aug 22) at 9PM.
| Wave Type | Time (CST) & Date | Wave Height & Period |
|---|---|---|
| Next good surf (1 star+) | 3PM (Mon 24th Aug) | 2.5ft (0.7m) 17s |
| Best Surf | 9AM (Fri 28th Aug) | 2.5ft (0.8m) 19s |
| Most Powerful | 6PM (Fri 28th Aug) | 3.5ft (1.1m) 18s |
Table - best surf conditions forecast for Avellanas Rivermouth over the next 16 days.
The Lowdown
Hey folks, Rusty here. Let’s talk about Avellanas Rivermouth. The long-range models are pointing to a solid run of surf, especially in the second half of the window, so keep your eyes peeled.
Right now, the wait is on. We’re looking at a gap of a few days from Friday, August 21st, through most of the following week, with only small, choppy, or poorly-timed waves. The water is a touch warmer than normal at 86°, about 3° above average for this time of year.
The first real highlight comes on Friday afternoon, August 28th. The swell is small at 2ft from the SW, but it’s packing serious punch with a 19-second period. That’s a long-period groundswell, and at a rivermouth, it should wrap in nicely. The wind goes light offshore from the W, making for clean, lined-up waves. It’s a smaller day, but the quality will be there for those who know the sandbar.
Then, the standout period kicks off. Saturday, August 29th, afternoon is the one to circle. The swell builds to 5ft from the SW, with a 16-second period, and the combined energy is pumping at 1415. The wind is light cross-offshore from the SW, keeping those faces clean. This is excellent surf, but at 5ft, it’s pushing into intermediate territory – not a beginner’s wave.
The run continues into the first week of September. Thursday, September 4th, morning looks magic: glassy conditions with the wind from the NNW at just 3 mph, and a solid 4ft SW swell at 17 seconds. That’s a long-period groundswell again, and the energy is strong at 1163. The break is fairly consistent, and with those conditions, you can expect excellent, clean waves for experienced surfers. The afternoon holds similar quality at 5ft.
Saturday, September 5th, morning is another gem. Glassy conditions, a 5ft SW swell at 16 seconds, and energy at 1053. The wind is a dead calm from the N, making for perfect, clean conditions. This is top-tier, but again, the size is more for the experienced crew.
Overall, the best on offer is the late-August and early-September window. The 29th afternoon and 4th/5th mornings are the true standouts. Keep in mind, this is a rivermouth, so the long-period groundswells should handle the shape well, but the crowd can be around sometimes. Get on it.
Rusty.
Short Range ForecastLight rain (total 3mm), mostly falling on Sat night. Warm (max 33°C on Fri morning, min 26°C on Fri night). Wind will be generally light. | Days 4-6 Weather SummaryLight rain (total 8mm), mostly falling on Tue night. Warm (max 31°C on Mon morning, min 25°C on Mon night). Wind will be generally light. | ||||||||||||||||||||
Friday 21 | Saturday 22 | Sunday 23 | Monday 24 | Tuesday 25 | Wednesday 26 | Thursday 27 | |||||||||||||||
AM | 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) | S 11 | S 11 | S 11 | S 11 | S 10 | S 10 | SW 19 | SW 18 | SW 18 | SW 18 | SW 17 | SW 16 | SW 16 | SW 16 | SW 15 | SW 15 | SW 15 | SW 15 | SW 18 | SW 18 | SW 16 |
Wave Graph  | |||||||||||||||||||||
 kJ | 286 | 297 | 284 | 223 | 158 | 153 | 184 | 260 | 330 | 255 | 305 | 322 | 211 | 206 | 191 | 110 | 107 | 75 | 111 | 155 | 254 |
Wind (km/h) | |||||||||||||||||||||
Wind State on-shore cross-onshore cross-shore cross-offshore off-shore glassy | cross-on | cross | on | cross-on | cross | on | cross-on | on | on | on | glassy | on | on | cross-off | on | cross-on | glassy | on | on | cross-off | on |
High Tide | 9:17PM1.72m | 9:41AM1.93m | 10:26PM1.67m | 10:47AM1.90m | 11:36PM1.70m | 11:51AM1.94m | 00:36AM1.79m | 12:46PM2.02m | 1:25AM1.93m | 1:34PM2.12m | 2:07AM2.08m | 2:16PM2.21m | 2:44AM2.22m | ||||||||
Low Tide | 3:14PM0.71m | 3:17AM0.81m | 4:20PM0.75m | 4:24AM0.86m | 5:27PM0.74m | 5:33AM0.85m | 6:26PM0.67m | 6:33AM0.78m | 7:14PM0.57m | 7:24AM0.68m | 7:54PM0.47m | 8:08AM0.56m | 8:31PM0.38m | ||||||||
 | |  | | |  |  |  |  | | | | | | | | |  | |  | | |
 | 5:33 | — | — | 5:33 | — | — | 5:33 | — | — | 5:33 | — | — | 5:33 | — | — | 5:33 | — | — | 5:33 | — | — |
 | — | 5:58 | — | — | 5:58 | — | — | 5:57 | — | — | 5:57 | — | — | 5:55 | — | — | 5:55 | — | — | 5:54 | — |
mm | — | — | — | — | — | 1 | — | 2 | — | — | 1 | — | — | 1 | 3 | — | 2 | 1 | — | 8 | 19 |
Temp °C | 33 | 32 | 29 | 33 | 31 | 27 | 32 | 32 | 27 | 31 | 30 | 28 | 31 | 28 | 28 | 30 | 28 | 26 | 30 | 28 | 26 |
Feels °C | 35 | 35 | 31 | 35 | 34 | 28 | 31 | 32 | 27 | 33 | 34 | 30 | 34 | 30 | 32 | 33 | 32 | 27 | 33 | 32 | 29 |
Swell 1 Height (m) Direction Period (s) | S 11 | S 11 | S 11 | S 11 | S 10 | S 10 | S 9 | S 9 | S 9 | S 9 | S 9 | SW 16 | S 9 | S 9 | SW 15 | S 7 | S 7 | S 7 | SSW 7 | SSW 7 | SW 7 |
| kJ | 286 | 297 | 284 | 223 | 158 | 153 | 109 | 106 | 106 | 104 | 102 | 322 | 55 | 53 | 191 | 46 | 44 | 57 | 77 | 99 | 184 |
Swell 2 Height (m) Direction Period (s) | SW 15 | SW 15 | SW 14 | SW 14 | SW 14 | NNE 5 | SSW 13 | SW 18 | SW 18 | SW 18 | SW 17 | S 9 | SW 16 | SW 16 | S 8 | SW 15 | SW 15 | SW 15 | SW 15 | SW 15 | S 7 |
| kJ | 76 | 75 | 100 | 95 | 155 | 17 | 116 | 260 | 330 | 255 | 305 | 76 | 211 | 206 | 46 | 110 | 107 | 75 | 76 | 106 | 111 |
Swell 3 Height (m) Direction Period (s) | SW 12 | N 5 | SW 17 | SW 21 | SW 20 | SW 13 | SW 19 | SW 13 | SW 12 | SW 12 | SW 12 | SW 12 | SW 12 | SW 11 | SW 11 | SW 11 | N 4 | SW 19 | SW 18 | SW 18 | SW 16 |
| kJ | 36 | 7 | 74 | 68 | 98 | 84 | 184 | 84 | 75 | 71 | 69 | 35 | 35 | 31 | 30 | 30 | 6 | 56 | 111 | 155 | 254 |
Wind waves Height (m) Direction Period (s) | NNE 5 | SW 6 | NNE 5 | NNE 5 | NNW 3 | — | N 5 | N 4 | NNE 4 | NNE 4 | — | N 5 | — | — | NNE 5 | NNE 3 | — | N 5 | NNE 4 | — | — |
| kJ | 7 | 10 | 7 | 5 | 3 | — | 8 | 28 | 24 | 9 | — | 12 | — | — | 9 | 2 | — | 11 | 6 | — | — |
Nearest Offshore or Glassy | |||||||||||||||||||||
Distance (km) | 7 | 8 | 1 | 19 | 1 | 1 | 19 | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 7 | 0 | 1 | 1 | 0 | 1 |
Best forecast wave conditions in Guanacaste | |||||||||||||||||||||
Best forecast wave conditions in Costa Rica | |||||||||||||||||||||
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Information about the Avellanas Rivermouth Surf forecast
The above surf forecast table for Avellanas Rivermouth provides essential information for determining whether the surfing conditions will be good over the next 16 days. A general guide to surfing at Avellanas Rivermouth can be found by selecting the local surf guide option on the grey menu. Our Avellanas Rivermouth 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 (Avellanas Rivermouth) 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 Avellanas Rivermouth 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.
Avellanas Rivermouth is 44 km (27 miles) from Nicoya. If you plan a holiday in Guanacaste, look for hotels and other accommodation in Nicoya. Nicoya has rooms for a wide range of budgets as well as car hire and transport links.
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