What is swell period and why does it matter? 

To mark Safer Boating Week, we thought we'd dive in and help boaties work out what sea conditions to expect when they see both sea state and swell mentioned in our coastal and recreational marine forecasts. To get you in the mood, let's talk about various states of discomfort that can be found on a boat. 

Many Auckland boaties head north for the summer break, up to the Bay of Islands and sometimes beyond, to the Cavalli Islands and Whangaroa Harbour. The prevailing southwest winds should mean a run up the coast. Right? Wrong. You need to know about the Northland lee trough.

The MetService team produces both coastal and recreational marine forecasts. Part of these forecasts includes the state of the sea and the swell. But what is the difference?

Firstly, it is important to understand how a wave is described. Figure one shows the different characteristics of a wave.