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

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

1,332 wave-buoy observations covered 28 of 30 days (93%). Typical wave height was 2.5 ft (10th–90th percentile 1.2–6.2 ft), while mean average of more than one wave period type was 9 seconds (10th–90th percentile 4.8–13.3 seconds). Mean water temperature was 10.4°C (10th–90th percentile 9.8–10.9°C). 21 of 5,289 checked values (0.4%) were excluded by quality control. Across 3 comparable years, mean wave height was below the same-month mean of 3.9 ft and mean wave period was above the same-month mean of 8.9 seconds.

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

Typical Significant Wave Height

2.5ft
Mean: 3.2 ft
P10–P90: 1.2 — 6.2 ft
Recorded extremes

0.8 — 11.3 ft

Mean Observed Wave Period

9secs
P10–P90: 4.8 — 13.3secs
Recorded extremes

2.9 — 18.2secs

Observed Wave Direction

Variable

Circular concentration: 25%

Most common: ESE (19%) · circular mean S

Mean Water Temperature

10.4°C
P10–P90: 9.8 — 10.9°C
Recorded extremes

9.8 — 12°C

Compared With Previous Aprils

Historical baseline from 2,145 observations across 3 years.

Wave Height
3.2ft
0.7ft below mean
Historical mean 3.871ft
Wave Period
9s
0.1s above mean
Historical mean 8.9s
Water Temperature
10.4°C
0.2°C below mean
Historical mean 10.6°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 2020Last observation shown
Metric
Mean significant wave height (ft)4114774222227764333343222211--
Mean maximum wave height (ft)622611107333331010106445464333222--
Mean peak period (s)751178111099791198767867101217131212119--
Mean zero-crossing period (s)5444576554565554444455665565--
Mean energy period (s)------------------------------
Mean reported period (s)76107811119107910108767767911161312121110--
Mean wave power, kilowatts per metre------------------------------
Mean peak wave directionESEconcentration 100%Econcentration 50%WNWconcentration 67%Sconcentration 56%Sconcentration 92%SSWconcentration 100%SWconcentration 91%SWconcentration 80%WSWconcentration 85%SSEconcentration 51%SWconcentration 63%WSWconcentration 62%Econcentration 77%ESEconcentration 100%ESEconcentration 100%ESEconcentration 66%ESEconcentration 48%Sconcentration 80%SSEconcentration 61%ESEconcentration 70%Variableconcentration 20%Wconcentration 61%Wconcentration 52%NWconcentration 57%WNWconcentration 63%WNWconcentration 45%Wconcentration 40%WSWconcentration 57%--
Mean directional spread (°)26.240.756.835.028.628.643.347.752.838.943.748.732.022.621.832.039.936.631.734.039.053.460.848.655.456.160.547.0--
Mean reported wave directionESEconcentration 100%ESEconcentration 51%Wconcentration 61%Sconcentration 56%Sconcentration 92%SSWconcentration 100%SWconcentration 86%SWconcentration 84%WSWconcentration 84%Sconcentration 39%SWconcentration 66%WSWconcentration 68%Econcentration 71%ESEconcentration 100%ESEconcentration 100%ESEconcentration 81%ESEconcentration 49%Sconcentration 78%SEconcentration 63%ESEconcentration 71%Econcentration 32%Wconcentration 46%Wconcentration 40%NWconcentration 49%WNWconcentration 55%WNWconcentration 44%WNWconcentration 46%WSWconcentration 57%--
Mean water temperature(°C)9.89.89.99.99.910.110.110.210.210.210.310.310.210.210.310.410.410.410.510.610.710.710.810.910.810.911.011.0--

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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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