Tue, 24 March 2015
Welcome to Wavescape Ocean Watch (WOW). We output marine forecasts 3x a day for 10 regions + more than 40 beaches. To make it easier, Spike analyses each region and presents a brief interpretation.
There are 10 pages for the ten main surfing regions (Namaqualand, West Coast, Cape Peninsula, Southern Cape, E Cape West, E Cape East, Wild Coast, South Coast, Durban and North Coast). Each page contains a summary (except Namaqua) at the top with a map indicating the regional boundaries. The summary is a manual analysis based on the automated data found below in the two graphical tables (bar graphs indicating open ocean forecast) and tabulated table below (showing beach forecasts and the regional forecast in more detail). Click on daily tabs to get the data.
All the data is based on the automated forecast at a virtual buoy (grid point) off the coast in each region. This grid point is identified in the top map of the region. For example, in the Cape Peninsula it is -34 S 17.5 E (a point west of Cape Town at 34° south and 17.5° east or 34°S 17° 30'E). You will also find other info: sea temperature, tides, sunrise and sunset, and wind speed according to the Beaufort scale. Also included are three animated maps (swell height, swell period and surface wind) for South Africa and links to live beach cams in each region. All the above data comes from NOAA (the National Oceanic and Atmospheric Administration), who run software called Wave Watch 3 through selected marine data extracted from the total (land and sea) data crunched from their numerical weather prediction model called the Global Forecasting System (GFS). We 'fetch' the WW3 data from NOAA and publish in different formats. You can also get to regions via a map of South Africa when you click the FORECAST button in the top navigation bar.
Included on each page is a BEACH FORECAST table, with info unique to specific spots. This is calculated using formulae that 'Spikerises' the regional forecast, filtering out the generic data based on topography, swell direction, swell energy and other factors that influence the transition from raw theoretical data to actual surf height. There are two types of entries in the BEACH FORECAST table, one marked with an asterisk, the other unmarked. An asterisk denotes the surf likely to be running along the coast at any open-ocean beach or reef in the area. You will notice these are usually a main coastal promontory or headland, such as 'Cape Point' or 'Cape Recife' south of PE. Unmarked beaches denote potential surf height at that specific beach. Carefully worded beaches such as 'Wild Coast Point' or 'South Coast Point' indicate potential surf at an 'average' pointbreak in a region to keep a balance between good info and blowing a spot's cover.
Period is key
You can make an informed call if you appreciate the key factor: wave period (the interval in seconds between swells in a set). Period is the average seconds it takes for the most dominant swell to pass a fixed point, not including other smaller swells around at the time.
Power to the period
The longer the period, the more powerful the swell, exponentially. A slight increase in period often means a big increase in swell power. Even if the height doesn't increase in the deep ocean, it's gonna increase BIG time when it encounters the sea floor at the coast.
Longer period swells move much faster than shorter period swells. They have longer wavelengths, and carry more energy that extends deeper into the ocean. Each energy pulse therefore moves more volume of water, which compresses higher (height) once the sea floor at the coast is encountered.
6' swell at 10 secs travels at HALF the speed of 6' swell at 20 secs
6' swell at 10 secs has 16 times less energy than a 6' swell at 20 secs
The 10 second swell arrives on the shore as a weak 2-3' wave.
The 20 second swell arrives on the shore as a potent 6-8' wave.
|HOW LONGER PERIOD BOOSTS LENGTH, SPEED AND WAVE SIZE *|
|BUOY HEIGHT||PEAK PERIOD||WAVELENGTH||SPEED||SURF AT COAST|
|WSW 10 ft||6 secs||56 metres||16.7 km/h||Sloppy 2-3'|
|WSW 10 ft||7 secs||76 metres||19.5 km/h||Weak 2-4'|
|WSW 10 ft||8 secs||99 metres||22.4 km/h||Weak 3-4'|
|WSW 10 ft||9 secs||126 metres||25.3 km/h||Soft 3-4'|
|WSW 10 ft||10 secs||156 metres||28 km/h||Soft 3-5'|
|WSW 10 ft||11 secs||188 metres||30.8 km/h||Med soft 4-5'|
|WSW 10 ft||12 secs||224 metres||33.7 km/h||Medium 4-6'|
|WSW 10 ft||13 secs||264 metres||36.5 km/h||Med solid 4-6'|
|WSW 10 ft||14 secs||306 metres||39.3 km/h||Solid 5-7'|
|WSW 10 ft||15 secs||351 metres||42 km/h||Solid 6-8'|
|WSW 10 ft||16 secs||400 metres||45 km/h||Big 8-10'|
|WSW 10 ft||17 secs||451 metres||48 km/h||Grinding 8-10'|
|WSW 10 ft||18 secs||505 metres||51 km/h||Dik 10-12'|
|WSW 10 ft||19 secs||563 metres||53.5 km/h||Dik 12'+|
|WSW 10 ft||20 secs||624 metres||57 km/h||Dik 15'|
This table pertains to the West Coast of SA and is a very rough estimate. The very westerly direction of the swell means it's coming straight on at your average reef or point. The table is a very simplistic and loose interpretation to generally indicate the exponential ratios between open ocean swell data and the potential wave when it hits the coast. In South Africa, we have many swell directions and coastal aspects facing in all directions.
Don't take the above too literally. Compare your break with the buoy data and BUILD YOUR OWN PROFILE. Different swells mean different things for breaks on SA's West, South or East Coast. This table is looking at a SW Cape area, assuming a swell direction of more or less WSW (call it 230 degrees, which is 5 degrees West of true SW at 225 degrees). In other words, the swell is quite West, coming quite straight onto an exposed break, but having undergone slight refraction. The surf at the coast is the POTENTIAL surf - a guesstimate based on rough calculations for above swells breaking on to a shallow reef or sandbar.
Where does the info come from?
The data comes from Wavescape Ocean Watch via the NOAA Wave Watch III model. It is updated three times a day. You get swell, wind and tide information for each of the above areas, including primary swell height & swell direction, as well as potential surf height and direction at the coast (in degrees). We have developed our own algorithms to pull out the data needed for the individual beach areas.