Avellanas Rivermouth Surf Break

Lat Long: 10.24° N 85.84° W

Avellanas Rivermouth Surf Forecast and Surf Report

Issued: 5 am 18 Aug 2026 (local time)

Forecast update in  hr  min

Today's Avellanas Rivermouth sea temperature is
30.0° C
1.9° 

Avellanas Rivermouth surf forecast is for near shore open water. Breaking waves will often be smaller at less exposed spots.


Avellanas Rivermouth surf forecast from 18 Aug 2026:

  • Best quality surf: Friday 21 Aug, 9PM (local time) - 4ft (1.2m), 11s period, S 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★+): Wednesday 19 Aug, 3PM (local time) - 3ft (0.9m), 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 Wednesday (Aug 19) at 3PM. The primary swell is predicted to be 0.9m and 14s period with a secondary swell of 0.8m 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. The largest open ocean swell (not directed at the beach) is 0.6m 4s period and expected on Sunday (Aug 23) at 12AM.

Wave TypeTime (CST) & Date Wave Height & Period
Next good surf (1 star+) 3PM (Wed 19th Aug)3ft (0.9m) 14s
Best Surf 9PM (Fri 21st Aug)4ft (1.2m) 11s
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 folks, Rusty here. Let’s have a look at what’s cooking at Avellanas Rivermouth.

We’ve got a bit of a slow start, but don’t write the week off just yet. The first few days are a mixed bag with some small, long-period groundswell from the SW, but the conditions are tricky. The water is sitting at 86°, which is a touch warmer than normal for this time of year.

The best action in the early part of the week looks like Friday afternoon, the 21st of August. The wind drops to glassy, dead calm, and we’ve got a 4 ft S swell pulsing in with an 11-second period. The combined energy is moderate (435), and with those clean, glassy conditions, it’s going to be a fun little session. It’s a sandbar setup, so it’s fairly consistent, but with those clean conditions, the crowds will likely be out.

Moving into the end of the month and into early September, the real standout is shaping up to be Saturday afternoon, the 29th of August. The swell is building to 4 ft from the SW, with a nice 16-second period, pushing the combined energy into strong territory (1028). The wind is glassy, and the forecast is calling for excellent conditions for experienced surfers. This is a long-period groundswell, which will be working magic at this rivermouth, offering up some proper shape. It’s the best on offer in the entire outlook, but remember, it’s a week and a half out, so it’s promising but not locked in.

After that, into the first couple of days of September, we see a drop in swell size but the window stays open. The Tuesday afternoon, the 1st of September and Wednesday afternoon, the 2nd of September both show clean, cross-off winds with SW swell around 3 ft to 4 ft, and the energy stays moderate (534 to 651). These are worth keeping an eye on for a solid, clean afternoon session.

So, overall, it’s a slow start, but the end of the month and the start of September have some real gems. The 29th of August is the one to circle on the calendar.

Stay stoked,
Rusty

Short Range Forecast

Heavy rain (total 30mm), heaviest during Tue afternoon. Warm (max 29°C on Tue morning, min 25°C on Tue night). Wind will be generally light.

Days 4-6 Weather Summary

Light rain (total 6mm), mostly falling on Sat afternoon. Warm (max 32°C on Sun morning, min 25°C on Sat night). Wind will be generally light.

Tuesday
18
Wednesday
19
Thursday
20
Friday
21
Saturday
22
Sunday
23
Monday
24
AM
PM
Night
AM
PM
Night
AM
PM
Night
AM
PM
Night
AM
PM
Night
AM
PM
Night
AM
PM
Night
Rating
(10 max)
2
1
1
0
2
1
0
2
1
1
2
2
0
1
0
0
2
0
0
2
0
Swell
Height Map
Height Map
Height Map
Height Map
Height Map
Height Map
Height Map
Height Map
Wave
Height (m)
Direction
Period (s)
1.1
SW
14
1
SW
14
1.1
SW
16
0.9
SW
15
0.9
SW
14
0.8
SW
14
0.6
SW
13
0.9
SSW
9
1.1
S
10
1.2
S
11
1.2
S
11
1.2
S
11
1.1
S
11
1
S
10
0.9
S
10
0.5
SW
19
0.6
SW
18
0.7
SW
18
0.6
SW
18
0.7
SW
17
0.8
SW
16
Wave Graph
Metric surfscale
Energy kJ
428
395
539
355
350
238
144
138
270
345
345
345
269
198
154
184
260
330
255
305
322
Wind (km/h)
10
E
5
SE
10
ENE
15
E
5
SSE
10
NE
25
ENE
15
S
5
E
10
NNE
0
SSW
5
SE
15
ENE
5
S
15
ENE
15
ENE
15
SW
20
ENE
20
ENE
15
SW
15
E
Wind State
on
cross-on
cross-on
on
glassy
cross-on
on
cross-off
on
cross-on
glassy
cross-on
cross-on
cross
on
on
cross-off
on
cross-on
cross-off
on
High Tide
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
11:51AM1.94m
00:36AM1.79m
Low Tide
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
5:33AM0.85m
6:26PM0.67m
thunderstorm
thunderstorm
thunderstorm
cloud
rain showers
cloud
part cloud
thunderstorm
thunderstorm
part cloud
part cloud
part cloud
part cloud
thunderstorm
clear
clear
thunderstorm
part cloud
part cloud
thunderstorm
part cloud
<span class="translation_missing" title="translation missing: en.weather_tables.sunrise">Sunrise</span>
5:33
5:33
5:33
5:33
5:33
5:33
5:33
<span class="translation_missing" title="translation missing: en.weather_tables.sunset">Sunset</span>
6:00
5:59
5:59
5:58
5:58
5:57
5:57
 mm
5
11
3
1
3
7
3
3
2
Temp °C
29
29
27
28
28
26
28
28
26
29
31
28
31
30
28
32
29
27
31
29
26
Feels °C
32
33
30
31
32
29
28
31
30
33
36
33
36
34
29
36
32
28
34
32
27
  • Map Icons:
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  • Live Wave Height (m)
  • Live Wind Speed (km/h)
  • Surf Rating (10 Max)
  • Ocean Swells (m)
  • Wind Speed (km/h)
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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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