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St Mary's Sound wave buoy daily means for Sep 2025

Daily means from the St Mary's Sound wave buoy for Sep 2025, including available wave height, period, direction, wind and sea temperature data.

Last observation shown

Data available:  to 

Monthly means for

Latest

Period Summary

Programmatically generated summary. Hog Says

1,422 wave-buoy observations covered all 30 days. Typical wave height was 4.1 ft (10th–90th percentile 1.8–6.7 ft), while the reported wave period averaged 5.1 seconds (10th–90th percentile 4–6 seconds). Mean water temperature was 15.4°C (10th–90th percentile 14.7–16.7°C). All 5,688 checked values passed quality control. Across 9 comparable years, mean wave height was above the same-month mean of 3.3 ft and mean wave period was below the same-month mean of 6.4 seconds.

Generated only from the observations and comparisons shown on this page.

Typical Significant Wave Height

4.1ft
Mean: 4.1 ft
P10–P90: 1.8 — 6.7 ft
Recorded extremes

1.2 — 10.2 ft

Mean Observed Wave Period

5.1secs
P10–P90: 4 — 6secs
Recorded extremes

3 — 8secs

Observed Wave Direction

SW

Circular concentration: 58%

Mean Water Temperature

15.4°C
P10–P90: 14.7 — 16.7°C
Recorded extremes

14.5 — 17.7°C

Compared With Previous Septembers

Historical baseline from 6,954 observations across 9 years.

Wave Height
4.1ft
0.8ft above mean
Historical mean 3.3ft
Wave Period
5.1s
1.3s below mean
Historical mean 6.4s
Water Temperature
15.4°C
In line with the historical mean
Historical mean 15.4°C

Chart showing grouped wave observations for St Mary's Sound. Use the table on this page for a text version of the same measurements. To open hourly observations, use a linked day name in the table.

About St Mary's Sound wave buoy

St Mary's Sound station lies between St Mary's and St Agnes in the Isles of Scilly. The National Network first deployed a Datawell Directional WaveRider here in May 2014, establishing a nearshore record for an archipelago exposed to Atlantic swell and important to local navigation and coastal management.

Its current data source reports wave height, wave period, wave direction, directional spread, wave power and sea temperature.

Metrics are rows; days run left to right.
St Mary's Sound wave buoy daily means Sep 2025Last observation shown
Metric
Mean significant wave height (ft)55763574655446746543432222QC rejected222
Mean maximum wave height (ft)------------------------------
Mean peak period (s)------------------------------
Mean zero-crossing period (s)------------------------------
Mean energy period (s)------------------------------
Mean reported period (s)556654665555556555455545545665
Mean wave power, kilowatts per metre------------------------------
Mean peak wave direction------------------------------
Mean directional spread (°)------------------------------
Mean reported wave directionWconcentration 70%SWconcentration 88%SSWconcentration 100%SWconcentration 98%WSWconcentration 86%Sconcentration 94%SSWconcentration 93%SWconcentration 99%SSWconcentration 99%SWconcentration 83%Wconcentration 83%WSWconcentration 81%WSWconcentration 88%SWconcentration 78%WSWconcentration 83%WNWconcentration 81%SWconcentration 99%WSWconcentration 90%WSWconcentration 90%WSWconcentration 76%Variableconcentration 19%Econcentration 99%ESEconcentration 65%NWconcentration 42%Variableconcentration 23%NWconcentration 68%Sconcentration 96%SSWconcentration 86%SWconcentration 94%WNWconcentration 81%
Mean water temperature(°C)16.416.916.716.716.716.615.715.515.315.014.914.914.915.114.915.515.415.415.315.215.215.115.014.914.814.814.614.714.714.6

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Wave metric colour key

Colours move through the scale as each number increases. They do not by themselves mean that conditions are good, safe or suitable for you.

Wave & swell height0–40+ ft
Wave & swell period0–22+ s
Wind speed0–75 mph

The displayed numbers remain the source of truth; colour is an additional visual cue.

What does buoy wave power mean?

kW/m means kilowatts of wave power per metre of wave crest. It describes the rate at which the observed sea state carries energy past the buoy.

Unlike the shore-directed forecast value, buoy wave power is the total power at the observation point. It is not projected towards a particular beach and does not predict breaking wave height.

In deep water, wave power can be calculated with:

P is approximately 0.49 times significant wave height squared times wave energy period.

P is power in kW/m, Hs is significant wave height in metres, and Te is wave energy period in seconds.

  • Provider-reported power is used when available.
  • Otherwise, a value is calculated only when both significant height and a genuine energy period are available. The ≈ symbol marks calculated values.
  • A dash is shown instead of substituting peak, Tm02, zero-crossing or other period measurements.
  • Daily and monthly figures use the mean of hourly-normalized observation power values; they are not calculated from mean height and period.

Wave direction, spectrum, water depth and local bathymetry still matter. Wave power is best read alongside height, period and direction rather than as a standalone surf-quality score.

The observation data displayed on this page is from the Regional Coastal Monitoring Programme.

Learn how SurfHog combines, checks and summarizes observations in the data and methodology notes.

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