How to Read Swelleye's Surf Report

Current Wave Data

Wave Direction:
• The direction that the swell is coming from.
• If you hover your mouse over the direction arrow, it will display the wave direction in degrees. As an example, if the wave direction is 90 degrees (as displayed above), it indicates that the waves are coming from the east.

Significant Wave Height:
• The average of the highest one-third (33%) of waves (measured from trough to crest) that occur in a given period. This is measured because the larger waves are usually more significant than the smaller waves. Since the Significant Wave Height is an average of the largest waves, you should be aware that many individual waves will be higher.
• Approximately 14% of waves will be higher than the Significant Wave Height (approximately 1 in every 7 waves).
• If you hover your mouse over the wave height unit, it will display both metric and imperial unit heights (m, ft).

Wave Period:
• The time it takes, in seconds, for successive waves to pass the same fixed point.
• Swelleye’s wave period reading is the mean period of the swell. Therefore, some wave sets will have a shorter period between waves, other sets will have a longer period between waves.
• Note that we include a decimal for this reading. This is because there could be a noticeable difference in wave height and quality between a wave period of 9 seconds and one of 9.9 seconds.

Current Wind Data

Wind Speed:
• The speed of air movement from one place to another place.
• If you hover your mouse over the wind speed unit, it will display all units speed (m/s, mph, kph, kn).
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Wind Direction:
• The direction that the wind is coming from.
• If you hover your mouse over the direction arrow, it will display the wind direction in degrees. As an example, if the wind direction is 340 degrees (as displayed above), it indicates that the wind is coming from NNW (north-northwest).

Wind Gust Speed:
• A rapid and temporary burst of stronger winds within a short period of time, typically lasting less than 20 seconds.
• Wind gusts are often associated with weather phenomena such as thunderstorms, cold fronts, and other turbulent atmospheric conditions.
• If you hover your mouse over the wind gust unit, it will display all units speed (m/s, mph, kph, kn).

Current Weather Data

Sunrise:
• The moment when the upper rim of the sun appears on the horizon in the morning.

Sunset:
• The disappearance of the sun below the horizon, with the actual sunset time being two minutes before the upper rim of the sun disappears below the horizon.

Weather Pictogram:
• Displays an icon of the current weather conditions (i.e. sunny, rainy, etc.).

Temperature:
• Displays the current air temperature, either in degrees Celsius (°C) or degrees Fahrenheit (°F).
• The temperature is calculated for 6 feet above ground.
• If you hover your mouse over the degrees unit, it will display degrees in both Celsius and Fahrenheit (°C, °F).

Sea Temperature:
• Displays the current water temperature of the sea, from sea surface down to approximately 10 feet below the surface.
• Note that water temperatures at the beach might be slightly warmer than indicated by the Sea Temperature reading.
• If you hover your mouse over the degrees unit, it will display degrees in both Celsius and Fahrenheit (°C, °F).

UV Index:
• Displays the maximum UV level for the day, typically occurring between 10 am and 2 pm.

Tide Data

• Normally, you will see 2 low tides and 2 high tides per day, called “Semi-Diurnal” tides. However, sometimes you will see only 1 low tide and 1 high tide. These are called "Diurnal" tides, and occur when the gravitational pull of the sun and moon are in alignment.
• The top number denotes the tide time (24-Hour time format).
• The number below the time denotes the tide height.
• The larger, orange circle denotes the current tide height.
• To understand the optimum tide for your surf break, see “Best Tide” in the “About” tab for that surf spot’s page ( example page here ).

Swelleye's Surf Report Data

In March of 2025, to provide improved surf report data, we updated both our weather model and marine wave model.

Weather Model
Our weather model provides data for temperature, wind speed, wind direction, wind gust speed, sunrise/sunset, and UV index. The data is generated using the GFS weather model (Global Forecast System), a highly accurate weather model that is updated 4 times a day (every 6 hours). GFS is made up of four separate models, all working together to produce accurate weather forecast data. GFS is one of the best models for forecasting ocean weather conditions.

Marine Wave Model
Our marine wave model provides data for wave height, wave direction, wave period, and sea temperature. The data is generated using the MFWAM wave model, which is updated twice a day (every 12 hours). The MFWAM wave model provides the highest spatial resolution for sea surface waves in the world.

While our surf reports are generally quite accurate (we update the data every 6 hours), please understand that there are many additional real-world variables to consider in surf forecasting. Influencing factors in surf forecasting are numerous, including location, coastal and seabed topography, swell direction, wind conditions, atmospheric pressure, tides, and more.

The forecasted waves are not always the same as the actual waves we surf, as the forecast data extrapolates offshore conditions to estimate nearshore wave conditions for surfers. Wave height data in our surf reports is based on wave crests and troughs detected by buoys in open waters, along with other data, and calculated using depth soundings. Therefore, the forecasted wave heights may differ from the observed wave heights near the shore where we surf.

To learn more about waves and surf forecasting, please read our blog articles here, here, and here!

We continue to optimize our surf forecasting system, in an effort to make it as accurate as possible. If you have any feedback and/or improvement suggestions, please contact us. We appreciate your valuable feedback, which will enable us to provide better services to you and all surfers in Taiwan.