alakaboo wrote:
I'm astounded surf forecasts 6 days out are ever right, frankly.
I take my hat off to anyone who can take remotely observed three-dimensional weather events, sometimes thousands of kilometres away, and translate that into what happens on the shoreline, without access to good bathymetrical info or a cohesive network of wave buoys.
A couple of knots or a couple of degrees of rotation difference and the forecast goes to water (so to speak).
Hi Alakaboo.
Even though you bring up these points of a couple of knots or degrees of rotation within a storm being hard to predict, in the bigger scheme of things, such little variations don't really affect a swell forecast.
This is because these storms form over 100-1000km's of ocean and little variations like this are lost in the broader swell production. Sure, if there's a little embedded low right off the East Coast, a burst of 50kt's will result in a larger spike in swell, but when we look at bigger storm systems, you get a good idea on how big a swell will be based on the dominant wind speeds, compared to a short-lived burst of stronger winds.
If we look to the Southern Ocean, swells can be forecast accurately out to 5-7 days or more due to the large distance between where the swell is being generated and where it will hit the coast.
Indonesia is a perfect example. Say we have a storm firing up today to the south of South Africa persisting over the next couple of days before weakening significantly.
I could make a prediction on swell size and arrival time 5-7 days out for this swell right now, and once the storm has disappeared in two days time, there's nothing that will change this forecast as the swell continues to travel towards Indonesia at a speed dependant on its period. The same goes for SA, Vicco, WA and Tas.
Trends in swell activity can be predicted even further out in the Southern ocean if you look at the positioning and movement of the Long Wave Trough. Here, have a quick read of this article and you'll see how..
http://www.swellnet.com.au/news/2318-lo ... eate-waves
The East Coast is a little different as the storms are closer to the coast and a lot more dynamic.
A dynamic system such as an ECL or deepening surface trough are tricky to forecast beyond a couple of days, and even harder day to day if the models don't agree, because their close-range nature means that we on the coast see these little intensifications and bursts of winds as ebbs and pulses of swell.
In saying this, general trends can be clearly seen out to 4-5 days such as when the peak of the swell will occur, when winds will swing offshore, and then how quick the swell will drop away.
I have also personally forecast swell episodes for the East Coast 7 days out as I know that we are going to move towards a particular weather pattern. The timing may change a little, but it gives people a heads up to keep their diary flexible in a week's time.
Keeping an eye on numerous weather charts every day gives you a great knowledge base and idea on how a particular weather system may evolve, even when the models diverge, and I use this knowledge in every forecast I pen up.
Your mate at the bureau who says that any weather forecast beyond 2 days isn't worth spit obviously doesn't know how to read trends in weather, and use all the data available to make a confident call beyond 2 days. This statement is ridiculous.
..mark each day u surf 
