surfingwomens

This was actually directed to the forecasts on www.wavewatch.com but I thought I would post it here too.Hi,I new to surf forecasting and I'm trying to get a better handle on wave period. From my reading I have found out that any swell with a period longer than 13 seconds is considered sizable. However when I review your surf forecasts for period the scale starts at 15 seconds. If you can help me