Buoy Johan Castberg
Source: MET Norway Frost
Short-period windswell
Height
4.5m
Hs
Period
7s
Tp
Direction
W
256°
Water
—
Last update: 1 Nov, 04:50
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About this buoy
Geographic location
Finnmark, Norway · 203.7 km offshore
Buoy Johan Castberg continuously measures essential oceanographic parameters for surfing and water sports. (72.484050° lat, 20.233930° lng)
Latest reading
On 1 November 2026 at 04:50 CET: 4.5 m significant wave height, 7 s period, from the W (256°).
Measured data
This marine station records significant wave height, maximum height, wave period, swell direction, and water temperature.
About this data source
This buoy's observations are supplied through MET Norway Frost by MET Norway.
How to read buoy data
Significant Height (Hs)
The average of the highest third of waves. This is the most representative measure of the wave size you'll see on the water.
Maximum Height (Hmax)
The highest wave recorded during the measurement period. Generally 1.5 to 2 times the significant height.
Period (Tp)
The time in seconds between two wave crests. A long period (>12s) indicates more powerful and consistent groundswell.
Direction
The direction the swell is coming from. The impact on the coast depends on the shoreline orientation.
Frequently Asked Questions
What's the difference between significant and maximum height?▼
Significant height (Hs) is the average of the highest third of waves, representing what you typically observe. Maximum height (Hmax) is the largest wave measured, often 1.5 to 2 times higher than Hs. A set of large waves can occasionally exceed Hs.
Why is the period important?▼
A long period (>12s) means waves have traveled far and carry more energy (groundswell). A short period (<8s) indicates local wind-generated swell, more disorganized. For surfing, longer periods produce more powerful and better-shaped waves.
How often is the data updated?▼
Buoys typically transmit their data every 30 minutes to 1 hour. The delay between measurement and display depends on the transmission network and our collection system.
Why doesn't the direction match the waves on the beach?▼
The buoy measures direction offshore. Waves change direction as they approach the coast due to refraction (seabed effect). Beach orientation and coastal obstacles also influence the final wave direction.