Effects of windswell on buoy readings..

I just though this might interest a few people.

Below is a graph of the wave buoy measurements off Cape du Couedic in South Australia (7.5km offthe coast to the west of Kangaroo Island).

http://www.bom.gov.au/products/IDS65030.shtml

Just to set the scene, a strong W/SW groundswell arrived overnight and peaked during the morning with Significant wave heights steadying around 3.5m as peak wave periods settled between 16-18 seconds.

Now winds were light and mostly variable during this peak of swell and both the Mid and South Coasts around Adelaide had excellent waves this morning.

A strong cold front and SW change hit during the late morning, with Cape Borda (on the West Coast of KI) showing winds tending SW at 26kts with gusts of 36kts at 10:45am...

http://www.bom.gov.au/products/IDS60801/IDS60801.95805.shtml

If we look back at the buoy readings we can that just after this time the average wave periods took a dive and both significant and maximum wave heights started to rise.

So you can see that the windswell associated with the strong SW winds has bought down the average periods because there is a lot of low period swell in the water mixed in with the groundswell, and wave heights have jumped due to the windswell adding to the groundswell already in the water.

If the periods stayed the same or even rose as well as the significant and maximum wave heights you could guess that a new stronger groundswell was filling in, but using this data without wind observations, you can see that it's contaminated with windswell.

I just though that this was a good example of how to interpret wave buoy readings, especially if you don't have wind observations near by, as you can use just the buoys observations to interpret that a change is moving through the area, or the arrival of a new groundswell/windswell.

Cheers, Craig