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St Mary's Sound wave buoy daily means for Apr 2021

Daily means from the St Mary's Sound wave buoy for Apr 2021, 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

714 wave-buoy observations covered all 30 days. Typical wave height was 2.2 ft (10th–90th percentile 1.2–7.5 ft), while the reported wave period averaged 4.4 seconds (10th–90th percentile 3–5 seconds). Typical wind was 0 mph and mean water temperature was 10.5°C (10th–90th percentile 10.3–10.7°C). 1 of 3,570 checked values (0%) were excluded by quality control. Across 4 comparable years, mean wave height was below the same-month mean of 3.7 ft and mean wave period was below the same-month mean of 8.9 seconds.

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

Typical Significant Wave Height

2.2ft
Mean: 3.2 ft
P10–P90: 1.2 — 7.5 ft
Recorded extremes

0.8 — 11 ft

Mean Observed Wave Period

4.4secs
P10–P90: 3 — 5secs
Recorded extremes

3 — 6secs

Observed Wave Direction

ESE

Circular concentration: 41%

Mean Water Temperature

10.5°C
P10–P90: 10.3 — 10.7°C
Recorded extremes

10.2 — 15.9°C

Available for 713 of 714 hourly samples

Compared With Previous Aprils

Historical baseline from 2,812 observations across 4 years.

Wave Height
3.2ft
0.5ft below mean
Historical mean 3.7ft
Wave Period
4.4s
4.5s below mean
Historical mean 8.9s
Water Temperature
10.5°C
In line with the historical mean
Historical mean 10.5°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 Apr 2021Last observation shown
Metric
Mean significant wave height (ft)464222112221233322223878962221
Mean maximum wave height (ft)------------------------------
Mean peak period (s)------------------------------
Mean zero-crossing period (s)------------------------------
Mean energy period (s)------------------------------
Mean reported period (s)555533445444444445444555654444
Mean wave power, kilowatts per metre------------------------------
Mean peak wave direction------------------------------
Mean directional spread (°)------------------------------
Mean reported wave directionSEconcentration 48%ESEconcentration 99%ESEconcentration 100%ESEconcentration 99%Nconcentration 69%ENEconcentration 88%NEconcentration 60%SSWconcentration 77%Sconcentration 99%Econcentration 67%ENEconcentration 77%Sconcentration 41%SSEconcentration 79%SSEconcentration 94%SEconcentration 79%SEconcentration 94%Variableconcentration 7%WNWconcentration 83%WNWconcentration 54%WSWconcentration 78%Variableconcentration 19%Econcentration 100%Econcentration 100%ESEconcentration 99%ESEconcentration 99%ESEconcentration 99%ESEconcentration 65%NNEconcentration 47%Econcentration 86%SSWconcentration 63%
Mean water temperature(°C)10.310.310.310.410.310.310.310.310.410.310.310.410.610.410.410.410.510.510.510.610.710.610.510.610.610.610.710.710.710.8

Swipe sideways to see more days.

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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