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

Daily means from the St Mary's Sound wave buoy for Dec 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

665 wave-buoy observations covered 29 of 31 days (94%). Typical wave height was 5.4 ft (10th–90th percentile 3.4–8.4 ft), while the reported wave period averaged 5.2 seconds (10th–90th percentile 4–6 seconds). Typical wind was 0 mph and mean water temperature was 11.9°C (10th–90th percentile 11.6–12.4°C). 2 of 3,325 checked values (0.1%) were excluded by quality control. Across 5 comparable years, mean wave height was above the same-month mean of 5.4 ft and mean wave period was below the same-month mean of 8.6 seconds.

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

Typical Significant Wave Height

5.4ft
Mean: 5.7 ft
P10–P90: 3.4 — 8.4 ft
Recorded extremes

2.2 — 11.3 ft

Available for 663 of 665 hourly samples

Mean Observed Wave Period

5.2secs
P10–P90: 4 — 6secs
Recorded extremes

4 — 7secs

Observed Wave Direction

SSW

Circular concentration: 42%

Mean Water Temperature

11.9°C
P10–P90: 11.6 — 12.4°C
Recorded extremes

11.5 — 12.5°C

Compared With Previous Decembers

Historical baseline from 3,689 observations across 5 years.

Wave Height
5.7ft
0.3ft above mean
Historical mean 5.4ft
Wave Period
5.2s
3.4s below mean
Historical mean 8.6s
Water Temperature
11.9°C
0.2°C above mean
Historical mean 11.7°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 Dec 2021Last observation shown
Metric
Mean significant wave height (ft)534544QC rejected55546643579777887646--108
Mean maximum wave height (ft)-------------------------------
Mean peak period (s)-------------------------------
Mean zero-crossing period (s)-------------------------------
Mean energy period (s)-------------------------------
Mean reported period (s)555555665555555556555566655--66
Mean wave power, kilowatts per metre-------------------------------
Mean peak wave direction-------------------------------
Mean directional spread (°)-------------------------------
Mean reported wave directionNWconcentration 41%Nconcentration 43%WSWconcentration 85%Wconcentration 69%NNEconcentration 33%WSWconcentration 59%SSWconcentration 87%Wconcentration 78%WSWconcentration 68%Wconcentration 89%Wconcentration 77%WSWconcentration 66%SWconcentration 96%SWconcentration 99%WSWconcentration 75%SEconcentration 69%ESEconcentration 100%ESEconcentration 100%ESEconcentration 99%ESEconcentration 99%ESEconcentration 99%SSEconcentration 87%SSWconcentration 95%SSWconcentration 98%SWconcentration 97%SWconcentration 98%SSWconcentration 92%--SSWconcentration 100%SWconcentration 98%
Mean water temperature(°C)12.512.412.412.312.212.212.111.911.911.811.811.811.911.911.911.811.811.811.711.711.611.611.611.611.611.611.6--11.711.7

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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