im very new to this
the lows produce the swell right?
and the lower the L the larger the swell
e.g most lows are around 1020
so.. whats the best guide for knowing how big it will be at ur local?
A very breif rundown for you,
yes lows do produce swell, not always the case that the lower the low the larger the swell.
WIND is what makes the swell, Low pressure systems are responsible for this. The Law of thermodynamics is that air will move from a region of high pressure to a region of low pressure, Ie air rushes out of a region to fill the space left by a low pressure system hence why low pressure systems are accompanies by winds, A good way to remember this is next time you Fart understand that the pressure inside your bowels exceeded the pressure outside your sphincter therefore air rushed out in an attempt to re balance the pressure inside and outside
. same thing happens outside, sun heats up air- hot air is less dense therefore it rises- cooler air then rushes to fills in the space left by the rising warm air.
When you look at a weather map you will see all these funky lines, they are called isobars and represent the atmospheric pressure, generally the closer the bars are together the lower the pressure and more wind there will be. Air rmoves clockwise around a low pressure system and anticlockwise around a high pressure system. So when you look at the map follow the isobars around and you will be able to tell a number of things
the most important are
1) whether the wind will be offshore at you beach
2) wheether there has been a low pressure system off the coast that may have produced the swell.
check out the ocean if you see a low pressure system in your areas swell window then follow the isobars around and see if there is an extended rregion of strong winds blowing towards you beach. the size of the swell will be determined by a number of things
1)the wind strength
2)the wind direction
4)the duration of the weather event-how long are the winds blowing for
3)the fetch, or the size of the area that has these winds blowing over. ie a tight low pressure system may have strong winds blowing east over a short fetch which may possibly lead to a swell the same size as a low pressure sysstem that had lighter winds but blew for longer or over a longer distance.
So the best guide is to keep an eye on the charts and see how low the low is, how large the fetch is and how long the sytem will last. couple that with what local winds are doing at your beach and you will have an idea of what condidtions will be like. Depending on where you live these the ease of exactly predicting swell size is very differrent. for example where i live in south oz we get swells that are produced from weather systems SW of western australia so these swells take a long time to get to the Adelaide coast, along the way they degrade in size or can even be blown flat by opposing winds from weather systems closer to the coast. QLD seems to get much shorter range swells that are produced fairly close to the coasts and take less time to reach the coast and lose less size.
thats where swell models come into play, unless youve been watching the weather charts for a very long time and know the ins and outs of these weather systems your better off looking at swell models such as surfline or http://www.lajollasurf.org/gblpac.html
which will predict the swell for you. However knowing the above details i set out for you and using bouy data you can then double check the swell models closer to the expected arrival date and make sure the swell is around and the winds are favourable for your chosen destination.
hope this helps, happy forcasting