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St Mary's Sound wave buoy daily means for Sep 2020

Daily means from the St Mary's Sound wave buoy for Sep 2020, 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

1,434 wave-buoy observations covered all 30 days. Typical wave height was 2.1 ft (10th–90th percentile 1.4–4.8 ft), while mean average of more than one wave period type was 8.5 seconds (10th–90th percentile 5.3–11.8 seconds). Mean water temperature was 15.2°C (10th–90th percentile 14.8–15.7°C). 23 of 5,654 checked values (0.4%) were excluded by quality control. Across 4 comparable years, mean wave height was below the same-month mean of 3.5 ft and mean wave period was above the same-month mean of 8.2 seconds.

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

Typical Significant Wave Height

2.1ft
Mean: 2.7 ft
P10–P90: 1.4 — 4.8 ft
Recorded extremes

1.1 — 9.9 ft

Mean Observed Wave Period

8.5secs
P10–P90: 5.3 — 11.8secs
Recorded extremes

3.1 — 16.7secs

Available for 718 of 719 hourly samples

Observed Wave Direction

WNW

Circular concentration: 42%

Mean Water Temperature

15.2°C
P10–P90: 14.8 — 15.7°C
Recorded extremes

14.6 — 17.3°C

Compared With Previous Septembers

Historical baseline from 2,568 observations across 4 years.

Wave Height
2.7ft
0.8ft below mean
Historical mean 3.51ft
Wave Period
8.5s
0.3s above mean
Historical mean 8.2s
Water Temperature
15.2°C
0.1°C above mean
Historical mean 15.1°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 2020Last observation shown
Metric
Mean significant wave height (ft)233222222122222267432125432225
Mean maximum wave height (ft)4553332322233333912742247643349
Mean peak period (s)7661010888899111111107788791179111091097
Mean zero-crossing period (s)444555444545445555555545555555
Mean energy period (s)------------------------------
Mean reported period (s)767101078-----------------------
Mean wave power, kilowatts per metre------------------------------
Mean peak wave directionSWconcentration 63%SWconcentration 84%SWconcentration 81%NNWconcentration 72%NWconcentration 59%WNWconcentration 75%NWconcentration 89%NWconcentration 92%NNWconcentration 94%NWconcentration 82%NWconcentration 66%NNWconcentration 98%NNWconcentration 90%NNWconcentration 84%WNWconcentration 58%SWconcentration 99%ESEconcentration 67%ESEconcentration 99%ESEconcentration 75%ESEconcentration 72%SEconcentration 34%WNWconcentration 74%WNWconcentration 76%WNWconcentration 82%NNWconcentration 99%WSWconcentration 32%WNWconcentration 89%WNWconcentration 91%WNWconcentration 83%SWconcentration 98%
Mean directional spread (°)40.639.641.450.359.255.957.454.656.753.749.653.260.855.958.335.924.920.733.636.846.861.948.845.552.952.758.660.453.634.6
Mean reported wave directionSWconcentration 63%SWconcentration 81%SWconcentration 78%NWconcentration 74%NNWconcentration 52%WNWconcentration 71%NWconcentration 83%-----------------------
Mean water temperature(°C)15.415.315.115.115.015.014.915.015.015.415.115.315.515.815.515.515.315.215.215.515.815.615.315.114.915.115.014.814.814.7

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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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