Data sources & licences

Wind

Forecast: weather data by Open-Meteo.com, licensed under CC BY 4.0 — model ECMWF IFS HRES, obtained through Open-Meteo.

The Rietvlei / Milnerton forecast comes from the model point used for Sunset Beach, a grid cell over Table Bay — the cell over the lagoon sits inland and reads too little wind there.

Fallback when it is unavailable: MET Norway, also CC BY 4.0.

Cape correction

In wind from southerly to westerly directions (SE to W), a forecast value on this site is shown not raw but as the model value times a fixed factor per spot — mean and gusts separately, strongest at Langebaan. The model’s 9 km grid cannot resolve the Cape’s thermal wind or the local wind effects around Langebaan lagoon, and it reads low in those directions. In every other direction, such as the north-westerly frontal winds, the model value stays as it is — the model resolves those. Each value is judged on its own wind direction, so the hour-by-hour chart is judged hour by hour. The factors come from local knowledge (as of 17 September 2026), not from a measurement series; they will be replaced by measured values once the comparison is in. Above a 40 kn model mean nothing is corrected. Wherever the factor applies, “ECMWF + Cape correction” stands under the figure, and the spot’s wind source names the raw model value beside it; where it does not, the stamp says “ECMWF” alone. A chart holding both kinds of hour carries “ECMWF, SE–W corrected”. A measured value is never corrected: the MAC measurement at Rietvlei stays as it is — only the hour-by-hour chart under it is model, and is corrected like everywhere else.

Measurement

Rietvlei measurement: MAC.

The minute-by-minute values in the “Readings · MAC” table at Rietvlei come from the Milnerton Aquatic Club’s weather station and are relayed through our own server. We also store these readings unchanged and show a 7-day summary from them: each day’s mean, its highest gust and the direction most of the wind came from.

Wind2Speed

Wind2Speed. The live measurements at Langebaan, Big Bay and Rietvlei / Milnerton come from Wind2Speed’s own stations — real anemometers at the spot, operated and published by Wind2Speed. We show their display with their kind permission; the rights to the measured values remain with Wind2Speed. wind2speed.africa

SkylineWebcams

SkylineWebcams. The live cam at Langebaan is streamed through the SkylineWebcams platform — embedded as their player, loaded only when you tap. Who operates the camera is credited under the tile. The rights to the live picture remain with SkylineWebcams and the camera’s operator. skylinewebcams.com

Rietvlei camera

The Rietvlei camera is operated by the Milnerton Aquatic Club; its picture is relayed through our own server so it can be shown over https. milnertonaquaticclub.co.za

Waves

Waves: MFWAM model by Météo-France (Copernicus Marine Service), obtained through Open-Meteo. marine.copernicus.eu

ECMWF notice

This service is based on data and products of the European Centre for Medium-Range Weather Forecasts (ECMWF), www.ecmwf.int, published under a Creative Commons Attribution 4.0 International (CC BY 4.0). ECMWF does not accept any liability whatsoever for any error or omission in the data, their availability, or for any loss or damage arising from their use.

Values are rounded to whole knots and interpolated to each spot’s coordinates.