Surf Forecasts:
Avellanas Rivermouth surf forecast from 18 Aug 2026:
- Best quality surf: Tuesday 18 Aug, 6AM (local time) - 3.5ft (1.1m), 14s period, SW swell with glassy winds.
- Most powerful swell: Tuesday 18 Aug, 9PM (local time) - 3.5ft (1.1m), 16s period, SW swell with 539 kJ wave energy.
- Next surfable swell (1★+): Tuesday 18 Aug, 6AM (local time) - 3.5ft (1.1m), 14s 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 Tuesday (Aug 18) at 6AM. The primary swell is predicted to be 1.1m and 14s period with a secondary swell of 0.9m and 8s. 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 16s and forecast to arrive on Tuesday (Aug 18) at 9PM. Winds are predicted to be onshore at the time the swell arrives.
| Wave Type | Time (CST) & Date | Wave Height & Period |
|---|---|---|
| Next good surf (1 star+) | 6AM (Tue 18th Aug) | 3.5ft (1.1m) 14s |
| Best Surf | 6AM (Tue 18th Aug) | 3.5ft (1.1m) 14s |
| Most Powerful | 9PM (Tue 18th Aug) | 3.5ft (1.1m) 16s |
Table - best surf conditions forecast for Avellanas Rivermouth over the next 16 days.
The Lowdown
Alright, grab your stick, let’s talk about the next couple of weeks here at Avellanas Rivermouth.
Right off the bat, we’ve got something to get excited about. The first slot on Monday the 17th of August is looking pretty damn sweet. The wind is glassy, absolutely dead calm, and we’ve got a clean 4ft SW groundswell pumping in. The water is 86° and a touch warmer than normal for this time of year, which is a nice bonus. The combined swell energy is chunky at 611 (moderate). It sets the week up nicely, but that’s the high point for the next few days.
Tuesday and Wednesday are a bit of a write-off for good surf. The wind swings cross-on or onshore, and conditions turn choppy or just plain messy. The swell hangs around 3ft to 4ft, but without the right wind, it’s not worth paddling out. There’s a brief window on Wednesday afternoon with glassy conditions, but the swell is only 3ft – small and clean, a possibility for a longboard if you’re desperate.
We see a pattern emerge from Thursday on. The mornings are pretty much all blown out by ENE wind, but many afternoons clean up nicely with light cross-off breezes. From Thursday the 20th through Sunday the 23rd, the afternoons offer clean, ridable waves in the 2ft to 4ft range. The combined swell energy sits around 300 to 466 (moderate). Nothing huge, but fun and user-friendly. The period is mostly 10 to 15 seconds, so there’s some shape.
Now, let’s talk about the standout. If you can wait, the end of the month is where it’s at. The real action starts kicking on Friday the 28th of August and carries through that weekend. Friday afternoon we see a solid 4ft SW groundswell with a period of 19 seconds and a massive combined energy reading of 1184 (strong). The wind is cross-off and clean. That’s a proper groundswell with real push.
Then Saturday the 29th of August into Sunday the 30th is the absolute pick of the entire period. Swell builds to 5ft, still from the SW, with periods around 15 to 17 seconds. The combined energy peaks at 1806 (strong to very strong) on Saturday morning, and even with a slight cross-on breeze in the morning, the afternoons clean right up with light winds. This is excellent, powerful surf. Now, 5ft is getting up there, so it’s going to be a bit much for beginners. For experienced surfers, this is prime. The long period (over 15 seconds) means the waves will have plenty of grunt, and being a rivermouth, it should handle that energy well, though be ready for longer lulls between sets. This window (August 28-30) is hands down the best on offer, though being more than a week out, keep an eye on the forecast for any changes.
We taper off into the first days of September with clean afternoons again, swell dropping back to 3ft to 4ft, with the combined energy settling back to moderate (502 to 686). Good fun, but nothing compared to that blast at the end of August. This spot is fairly consistent, so even if the mornings are a write-off, there’s usually a clean afternoon session to be had.
Stay safe out there.
- Rusty
Short Range ForecastModerate rain (total 17mm), heaviest on Mon afternoon. Warm (max 31°C on Thu morning, min 24°C on Wed night). Wind will be generally light. | Days 5-7 Weather SummaryLight rain (total 8mm), mostly falling on Sat morning. Warm (max 32°C on Sun morning, min 25°C on Thu night). Wind will be generally light. | |||||||||||||||||||
Mon 17 | Tuesday 18 | Wednesday 19 | Thursday 20 | Friday 21 | Saturday 22 | Sunday 23 | ||||||||||||||
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) | SW 14 | SW 14 | SW 14 | SW 14 | SW 16 | SW 15 | SW 14 | SW 14 | SW 13 | S 8 | S 11 | S 11 | S 11 | S 11 | S 11 | S 10 | S 10 | SW 19 | SW 18 | SW 18 |
Wave Graph | ||||||||||||||||||||
500 | 410 | 428 | 395 | 539 | 355 | 350 | 238 | 183 | 147 | 275 | 345 | 351 | 284 | 269 | 198 | 154 | 184 | 260 | 327 | |
Wind (km/h) | ||||||||||||||||||||
Wind State on-shore cross-onshore cross-shore cross-offshore off-shore glassy | glassy | on | cross-on | cross-on | on | on | glassy | cross-on | on | glassy | glassy | on | cross-off | glassy | cross-on | cross-off | on | on | cross-off | on |
High Tide | 6:01PM2.29m | 6:23AM2.44m | 6:44PM2.14m | 7:05AM2.29m | 7:29PM1.98m | 7:50AM2.14m | 8:18PM1.83m | 8:41AM2.01m | 9:17PM1.72m | 9:41AM1.93m | 10:26PM1.67m | 10:47AM1.90m | 11:36PM1.70m | |||||||
Low Tide | 00:07AM0.28m | 12:41PM0.36m | 00:48AM0.43m | 1:27PM0.49m | 1:31AM0.58m | 2:16PM0.61m | 2:20AM0.71m | 3:14PM0.71m | 3:17AM0.81m | 4:20PM0.75m | 4:24AM0.86m | 5:27PM0.74m | ||||||||
— | — | 5:33 | — | — | 5:33 | — | — | 5:33 | — | — | 5:33 | — | — | 5:33 | — | — | 5:33 | — | — | |
6:00 | — | — | 6:00 | — | — | 5:59 | — | — | 5:59 | — | — | 5:58 | — | — | 5:58 | — | — | 5:57 | — | |
mm | 4 | 2 | 2 | 7 | 2 | — | — | — | — | 1 | 2 | — | — | — | 2 | 3 | — | — | — | — |
Temp °C | 29 | 26 | 30 | 28 | 26 | 28 | 28 | 26 | 31 | 30 | 26 | 29 | 29 | 27 | 30 | 30 | 27 | 32 | 30 | 27 |
Feels °C | 34 | 30 | 32 | 31 | 28 | 30 | 32 | 28 | 34 | 34 | 29 | 34 | 31 | 32 | 33 | 32 | 29 | 36 | 33 | 28 |
Swell 1 Height (m) Direction Period (s) | SW 14 | SW 14 | SW 14 | SW 14 | SW 16 | SW 15 | SW 14 | S 8 | SSW 8 | S 8 | S 11 | S 11 | S 11 | S 11 | S 11 | S 10 | S 10 | S 9 | S 9 | S 9 |
500 | 410 | 428 | 395 | 539 | 355 | 350 | 111 | 115 | 147 | 275 | 345 | 351 | 284 | 269 | 198 | 154 | 109 | 106 | 109 | |
Swell 2 Height (m) Direction Period (s) | S 8 | S 7 | S 8 | S 8 | S 8 | S 8 | S 8 | SW 14 | SW 13 | SW 13 | SW 13 | SW 15 | SW 15 | SW 14 | SW 14 | SW 14 | SW 13 | SSW 13 | SW 18 | SW 18 |
111 | 108 | 98 | 100 | 95 | 89 | 90 | 238 | 183 | 138 | 83 | 76 | 54 | 102 | 95 | 155 | 84 | 116 | 260 | 327 | |
Swell 3 Height (m) Direction Period (s) | N 3 | S 10 | S 10 | N 4 | S 12 | N 5 | NNW 5 | N 6 | S 13 | S 13 | SSW 19 | SW 12 | SW 12 | SW 17 | N 4 | SW 20 | SW 20 | SW 19 | SW 13 | SW 12 |
2 | 18 | 17 | 3 | 3 | 19 | 4 | 3 | 13 | 30 | 36 | 36 | 36 | 74 | 3 | 98 | 97 | 184 | 84 | 75 | |
Wind waves Height (m) Direction Period (s) | — | — | — | — | NNE 5 | — | — | NNE 5 | NNE 5 | N 3 | NNE 4 | — | — | — | — | — | NNE 4 | NNE 4 | N 5 | NNE 4 |
— | — | — | — | 26 | — | — | 7 | 4 | 1 | 2 | — | — | — | — | — | 6 | 18 | 16 | 9 | |
Nearest Offshore or Glassy | ||||||||||||||||||||
Distance (km) | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 1 | 68 | 0 | 1 | 0 | 1 | 1 | 0 | 1 |
Best forecast wave conditions in Guanacaste | ||||||||||||||||||||
Best forecast wave conditions in Costa Rica | ||||||||||||||||||||
Header Global | ||||||||||||||||||||
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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.











