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St Mary's Sound wave buoy monthly means for 2021

Monthly means from the St Mary's Sound wave buoy for 2021, including available wave height, period, direction, wind and sea temperature data.

Last observation shown

Data available:  to 

Latest

Period Summary

Programmatically generated summary. Hog Says

8,643 wave-buoy observations covered 363 of 365 days (99%). Typical wave height was 3.1 ft (10th–90th percentile 1.4–7.5 ft), while the reported wave period averaged 4.9 seconds (10th–90th percentile 4–6 seconds). Typical wind was 0 mph and mean water temperature was 12.7°C (10th–90th percentile 10.1–15.6°C). 6 of 43,215 checked values (0%) were excluded by quality control.

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

Typical Significant Wave Height

3.1ft
Mean: 3.9 ft
P10–P90: 1.4 — 7.5 ft
Recorded extremes

0.7 — 16.7 ft

Available for 8,639 of 8,643 hourly samples

Mean Observed Wave Period

4.9secs
P10–P90: 4 — 6secs
Recorded extremes

3 — 9secs

Observed Wave Direction

SW

Circular concentration: 39%

Mean Water Temperature

12.7°C
P10–P90: 10.1 — 15.6°C
Recorded extremes

9.4 — 19.8°C

Available for 8,641 of 8,643 hourly samples

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 daily observations, use a linked month 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; months run left to right.
St Mary's Sound wave buoy monthly means 2021Last observation shown
Metric
Mean significant wave height (ft)58434233343QC rejected
Mean maximum wave height (ft)------------
Mean peak period (s)------------
Mean zero-crossing period (s)------------
Mean energy period (s)------------
Mean reported period (s)565455445555
Mean wave power, kilowatts per metre------------
Mean peak wave direction------------
Mean directional spread (°)------------
Mean reported wave directionSSWconcentration 48%SSWconcentration 65%WSWconcentration 45%ESEconcentration 41%SWconcentration 75%Variableconcentration 28%SWconcentration 45%SWconcentration 45%SWconcentration 30%SWconcentration 73%Variableconcentration 28%SSWconcentration 42%
Mean water temperature(°C)10.310.010.210.511.213.215.315.515.814.413.211.9

Swipe sideways to see more months.

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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