Now I don't know much about swell tracking or reading or much of that sort.
But I was wondering why sometimes swells tracked at larger heights, are posted as smaller on the chart? For instance, at 2pm sunday in monmouth county, it is listed as 4.6 feet. while 2 hours later it is listed as 3.0 with a second swell of 3.6. Why, on the chart, is that second set of swells listed as chest high while the 4.6 swell is listed as between waist and chest?
Its hard to say without looking at the data you were seeing, but the swell height is only part of the equation, the swell period and swell direction are also important.
The model is outputting swell energy for a point 5-10+ miles offshore (depending on the area). If the swell is moving parallel or away from the coast, you are not going to see 100% of the swell energy at the beach.
Also, swell period is a major factor. So, a swell is 4 ft @ 5 seconds will be about waist high or so, while a swell of 3 ft @ 14 seconds could be chest high+ on the beach.
The most important thing to keep in mind, is that swell heights that are output from the model are for the open ocean and not at the beach. Swellinfo interprets the data and forecasts a surf height for the local breaks.
i was visiting my grandpa a couple years ago in va beach on sat night in early august and it was chest-shoulder, lots of fun from an early hurricane. the next morning (sunday) was terrible down there, knee high on set, while my buddies in NJ were getting OH bombs
You also have to look at more information than just the buoy reading.
The reading you are seeing on the forecast page is just the DOMINANT wave height and period. This does not necessarily mean you will be seeing this at all. I use the tools on my favorite fishing site fryingpantower.com to get detailed swell information that will give a more clear estimate.
For instance, right now in WB:
41110 August 24, 2012 10:21 am EDT
Location: 34.141N 77.709W
Significant Wave Height: 3 ft
Dominant Wave Period: 15 sec
Average Period: 3.8 sec
Mean Wave Direction: ESE (115°)
Water Temperature: 81°F (27.2°C)
You would think by this data there should be at least chest high closeouts here. But, look at this http://wblivesurf.com. Knee, barely over shorebreak.
I see that the real swell is much smaller with a shorter period and coming from at least 90 degrees in another direction, which is causing it to jack up every once in a while offshore in an interaction with the barely sizable longer period ground swell (which I bet is really 1' at about 25 seconds right now) and causing the buoy to report a false dominant swell and period (I believe it's called a "node"). As the ground swell really begins to fill in it will overpower the wind swell and give the buoy enough push to give a more accurate reading. Or, at least that is how I understand it.
So, when the buoys are giving false readings in this situation, it will ultimately cause a forecast for on-shore wave height to also be inaccurate.