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Greenwich wave buoy daily means for Apr 2021

Daily means from the Greenwich 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

659 wave-buoy observations covered all 30 days. Typical wave height was 1.3 ft (10th–90th percentile 0.7–3 ft), while mean reported wave period; measurement type unavailable was 5.4 seconds (10th–90th percentile 4–7 seconds). Typical wind was 17.2 mph (10th–90th percentile 6.9–28.9 mph) and mean water temperature was 9°C (10th–90th percentile 8.6–9.4°C). 12 of 3,295 checked values (0.4%) were excluded by quality control. Across 10 comparable years, mean wave height was below the same-month mean of 2.1 ft and mean wave period was below the same-month mean of 6.5 seconds.

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

Typical Wave Height

1.3ft
Mean: 1.6 ft
P10–P90: 0.7 — 3 ft
Recorded extremes

0 — 7.2 ft

Mean Wave Period

5.4secs
P10–P90: 4 — 7secs
Recorded extremes

2 — 9secs

Available for 650 of 659 hourly samples

Mean Water Temperature

9°C
P10–P90: 8.6 — 9.4°C
Recorded extremes

8.2 — 11°C

Typical Wind

NNE, 17.2mph
Mean: 17.8 mph
P10–P90: 6.9 — 28.9 mph
Recorded extremes

0 — 38 mph

Circular concentration: 49%

Available for 656 of 659 hourly samples

Compared With Previous Aprils

Historical baseline from 6,416 observations across 10 years.

Wave Height
1.6ft
0.5ft below mean
Historical mean 2.1ft
Wave Period
5.4s
1.1s below mean
Historical mean 6.5s
Water Temperature
9°C
0.7°C below mean
Historical mean 9.7°C

Chart showing grouped wave observations for Greenwich. 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 Greenwich wave buoy

Greenwich Lightship (WMO 62305) is a UK Met Office station in the southern North Sea on the Greenwich meridian. It monitors marine conditions between the Dover Strait and the Thames approaches. The station feed can include wind, wave height, pressure, visibility, and air and sea temperature.

Metrics are rows; days run left to right.
Greenwich wave buoy daily means Apr 2021Last observation shown
Metric
Mean wave height (ft)333122210121111111112322431121
Mean observed period(s)6Reported6Reported6Reported5Reported5Reported5Reported5Reported5Reported5Reported5Reported5Reported5Reported5Reported5Reported5Reported5Reported5Reported7Reported8Reported8Reported7Reported6Reported5Reported5Reported6Reported6Reported5Reported5Reported5Reported5Reported
Mean wave power(kW/m)------------------------------
Mean wind directionNEconcentration 98%NEconcentration 95%NEconcentration 98%NNWconcentration 42%NNWconcentration 82%NNWconcentration 95%NWconcentration 91%WSWconcentration 79%Wconcentration 93%NEconcentration 69%NNWconcentration 82%WNWconcentration 55%SWconcentration 77%NEconcentration 70%NEconcentration 94%NEconcentration 96%NEconcentration 94%Variableconcentration 24%Econcentration 44%ENEconcentration 83%NEconcentration 96%ENEconcentration 99%ENEconcentration 98%ENEconcentration 97%ENEconcentration 97%NEconcentration 97%Nconcentration 66%NEconcentration 92%NWconcentration 71%NNEconcentration 46%
Mean wind speed (mph)30282515242219119172011814191916971021282427322810151810
Mean water temperature(°C)9.39.19.09.19.08.68.58.89.08.88.78.78.98.98.88.98.99.39.79.49.29.09.19.19.08.99.39.39.49.5

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.

Which wave period is shown?

The table shows the best period measurement supplied for each observation. It is not necessarily the energy period used to calculate wave power.

Tp
Peak period: the period at the strongest spectral peak.
Tavg
The provider's average wave period.
Tm02
A mean period calculated from the wave spectrum.
Tz
Mean zero-crossing period.
Reported
A legacy value whose period type was not recorded.
Mixed
A daily or monthly mean containing more than one period type.

Wave power needs a genuine energy period (Te). SurfHog does not substitute Tp, Tavg, Tm02 or Tz when Te is missing.

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.

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