Tides and atmospheric pressure

So I've been watching the difference between predicted and actual tide as happening in south west WA. We have had a series of Low pressure systems moving through, noticed a 40% increase in actual to predicted the other day. Understand the cause of difference due to atmospheric pressure. Does anyone know the pressure at which the tide forecast is based on. Mean of pressures across the year? Maybe I can use this info to help me predict the difference between actual and predicted and get some more waves. Reckon I've got a fix on ideal tide for several of my fav spots.

cheers
PK