How it works
What this site is
Sideshore is a free, non-commercial kitesurfing forecast for Kite Beach, Blouberg (Table View, Cape Town): seven days ahead, hour by hour. There are no ads and no accounts. Your settings stay on this device.
Where the numbers come from
We combine four weather models at grid cells over the sea near Kite Beach: ECMWF IFS (9 km), DWD ICON (11 km), NOAA GFS and Météo-France ARPEGE (25 km). The headline wind is their weighted median, with weights 0.40, 0.27, 0.20 and 0.13. The UK Met Office model is not used, because its licence would require us to share our derived data under share-alike terms.
The technical detail
Direction is the circular mean of the model directions, weighted by weight × speed. Gusts are the headline wind times a gust factor: the weighted median of gust ÷ wind from the models whose sea-cell gusts are realistic here (ICON and ARPEGE gusts are unrealistically high over water at Kite Beach). Weather (air temperature, rain, thunder risk, fog) comes from the land cell. Waves and sea temperature come from a marine model cell about 15 km offshore.
Why we say "uncalibrated"
There is no wind measurement at the beach. At Kite Beach the combined forecast reads about 4.6 kn below Cape Town International airport in south and south-east winds. So every rating comes straight from the models, and we label it that way.
"Likely stronger" at Blouberg
For Kite Beach in winds from 110–200°, we also show a "likely stronger" figure: U = min(1.16 × H + 3, H + 8) knots, with gusts scaled the same way. It comes from comparing Cape Town airport observations (20 km away, inland) with the forecast at the Kite Beach sea cells in Dec 2025–Feb 2026. It is not measured at the beach.
We use it only to make warnings stricter (too strong, gusty) and to suggest one kite size smaller. It never raises a rating.
Direction classes
Kite Beach has a beach angle of 244° (west-south-west): the direction from which the wind blows straight onshore. We compare the wind direction with it:
| Class | Angle from dead onshore | Rating factor (open water) |
|---|---|---|
| Onshore | up to 30° | 0.6 |
| Cross-onshore | 30–70° | 1.0 |
| Cross-shore | 70–110° | 0.9 |
| Cross-offshore | 110–140° | 0.3 |
| Offshore | over 140° | 0 (No-go) |
The beach angle comes from map data and has not yet been checked on site. The classic summer south-easter (SE–SSE) is cross-shore here.
The technical detail: the uncertainty rules
We classify the consensus direction against the beach angle. Then at most one adjustment, and only ever toward offshore:
- U1 (spread): if the models disagree on direction by more than 30° (circular spread), we move one class toward offshore.
- U2 (offshore margin): otherwise, if the wind is cross-offshore within 15° of offshore (angle 125–140°) and at least one model (5 kn or more) already shows offshore, we call it offshore.
There is no margin at any other boundary, so the classic Blouberg south-easter (135–170°) stays cross-shore unless the models disagree widely.
Seven days, hour by hour
The home page shows today (or tomorrow, once today's windows are over), then the next seven days. Each day shows its rating, the best window, the peak wind and gusts, the main direction, a kite size for your settings, the confidence and any alert. Tap a day to open its hourly forecast. The further ahead, the lower the confidence; some models stop after a few days (ARPEGE after about 4), and those hours say how many of the four models remain.
The kiteability rating
Each hour gets a rating from 0 to 100 for your rider level: wind strength for your level × direction × gustiness × weather × tide × daylight. Bands: Good 75 and over, Kiteable 50–74, Marginal 25–49, Poor 1–24. A zero shows its reason (too light, too strong, offshore, thunder, dark). Confidence is shown next to the rating, not mixed into it.
| Level | Min | Ideal | Max | Cut-off | Gust cut-off |
|---|---|---|---|---|---|
| Beginner | 12 | 14–18 | 20 | 24 | 28 |
| Intermediate | 12 | 15–25 | 30 | 35 | 40 |
| Advanced | 14 | 18–32 | 38 | 42 | 48 |
| Foil | 8 | 10–18 | 22 | 26 | 30 |
A kite window is two or more daylight hours rated 50 or more. Any hour with a red alert counts as zero, so it splits a window. Daylight means from 15 minutes after sunrise to 15 minutes before sunset.
Confidence
Confidence combines how well the four models agree on strength and direction, the spread of the 51-member ECMWF ensemble, and how far ahead the forecast is (it drops after two days). High is 0.70 and over, Medium 0.40–0.69, Low under 0.40. If the ensemble is unavailable, confidence comes from the four models only.
The chance of kiteable wind uses the ensemble members, rescaled to the headline wind, so it follows the same headline as the rating.
Alerts
Red alerts mean No-go for your setting and override the rating: offshore wind; too strong or too gusty for your level; thunderstorm risk. Amber alerts are cautions: cross-offshore, strong for your level, gusty, wind shift, fog. Notes cover cold water, sunset, whales and low confidence. Red and amber alerts cannot be dismissed and always show the values that triggered them.
Tides
We predict the Cape Town tide ourselves from harmonic constants fitted to tide-gauge records (University of Hawaii Sea Level Center) and convert it to chart datum using the published SANHO mean level. It is an astronomical prediction: weather can change levels by ±0.3 m. At Kite Beach the tide mainly changes the beach width and the shore break, so it does not change the rating.
"Now" and estimates
The nearest observation is the Cape Town International airport report, 20 km inland. It is never "at the beach". The estimate adjusts the next three hours of forecast by how today's airport reading compares with what the models expected there, fading over about 1.5 hours. The adjustment is only calibrated for December to February, so outside that season the estimate is off. Estimates return in December.
What we can't do well
- Beach-scale gusts, wind shadows and acceleration.
- Waves close to shore.
- Where and when thunderstorms happen.
- Absolute calibration of any forecast without measurements at the beach.
Help us improve
Beach wind stations and kite schools would make these forecasts much better. If you run a station or a school at Blouberg and would like to help, contact the site owner (contact details to follow).