What is La Nina and why is it being talked about at the moment?
There is a lot of talk at the moment about La Nina and for good reason - all the major climate models agreeing that Eastern Australia is currently within a La Nina period and that it will persist until at least early next year. Key criteria for a La Nina to be declared are:
Sea surface temperatures within the eastern Pacific Ocean are 0.8 degrees cooler than average
Trade winds have been stronger than average in the western or central Pacific during any three of the past four months
Southern Oscillation Index (SOI), a measure of the difference in pressure between Tahiti and Darwin, is +7 or higher
Majority of climate models show sustained cooling of at least 0.8C below average in the eastern pacific until the end of the year
It’s not just Eastern Australia, with our friends in Western Australia seeing the Indian Ocean Dipole (IOD) going negative. We will need to wait and see what exactly transpires, but forecasts are suggesting above average rainfall across much of Australia during spring. Summer rainfall is also expected to be above average across eastern Australia during La Niña.
Without getting too technical, it seems the current climate outlook is for a wet few months ahead – where, when and how much rain is difficult to predict, but it will come… Keep an eye out for our next post which will look at what does this mean for construction sites and some guidance on wet weather preparation.
Image source: BoM Chance of Above Median Rainfall – November to February (3 month outlook)