Can someone give me a description of the three swell groups and what they mean in relation to each other? Some days there may be one to three swell groups at any given time of the day. What is best etc?
Click the "Swell" button and the "Swell Table" button. You will see the following explanation of the swell table data: The six rows represent different swell groups. The swell group colors match those on the SWELLS timeline graph above. There are 3 rows of data in each swell group: swell height(top), swell period(middle), and swell direction(bottom). Click the Day links at the top to view hourly swell data for the specific day.
Swells are generated by weather phenomena, and have a height, period (time between peaks), and a direction given in degrees. There are usually multiple swells (swell groups) that are heading toward the area referred to by the particular table. By looking at the table you can get all this information and also determine the dominate swells for your area.
This is my take. I am not an oceanographer, nor did I stay at a holiday inn express last night, so other SI members please enhance / correct. I hope it helps.
At any given moment, there is wave energy coming from the entire 360 degree spectrum. Through statistical analysis, the swell groups coming from specific events can categorized to give you a better way to understand the wave energy picture. In general, you will only need to know the 1 or 2 swells with the most energy, and disregard minor background energy.
On the East Coast, most of the time, only the primary swell group is of concern, as storm systems push off the coast and head east. However, if you have a coastal storm, and then, say a tropical storm, then you will have 2 primary events producing swell energy. Perhaps a tropical swell from the ESE at 4ft @ 14 seconds, and a coastal storm producing a S swell at 6ft @ 8 seconds. So, being able to separate these 2 swells from the entire spectrum is very helpful in understanding the scenario at any given moment.
On the West Coast, they often have multiple significant swells, since their wave energy is often produced many thousands of miles away in both the Northern and Southern Hemispheres.
Many thanks, that's just what I was looking for as a beginner scuba diver w/i 10miles of the shore. Looking for low waves and long periods, but was somewhat confused by there being up to three somewhat conflicting swells. A great site.