i think predicting weather patterns is very do-able in advance. however, nailing swells down to the exact size/wind/direction is much more difficult. you must allow some leeway with this as forecast models can change i think a cool addition to this site would be a monthly or periodic synopsis of current and predicted weather patterns, a recap of what we saw in past months and why, and what we can expect in the near future. something like this : http://tahoeweatherdiscussion.com/
Just like the hurricane center changes storm tracks daily the NWS changes the weather forecast. Weather dictates swell size and direction thus changes can occur. The NWS, Hurricane Center and NOAA love to give long range predictions and occasionally they're right. You can also flip a coin and be right half the time. They use multiple computer models and usually split those down the middle. For those that preach global warming, I say sure after every Ice Age there's global warming and this can occur on a micro level also. In the end jet streams control the weather and that's something we'll never be able to predict to far ahead IMO opinion of coarse...
Butterfly flaps his wings and it all goes to crap... or it sets up perfectly... This is when I envy you "eyes on" guys, they check it and go, no go... and never miss a swell!
I dont think you understand the concept of a swell forecast, or really any kind of forecast, if you have to ask this question. being SURE about something, and forecasting something, will always be two different animals.
just to clarify, the storm is coming in hot tonight (nowish) for the jersey area. this will be the swell maker. this is what we meant by the maybes. since the storm is over us now, we can be certain, to a degree, of what it will produce. this is what i meant before when talking about the "window". it cant alter much now that it is over us and its swell is much easier to predict. however, the swell will be quick and not last long. look for some barrels with that strong offshore wind too