The seasonal cooling off the NW coast

A lot of debate going on around the traps about the Indian Ocean, currently cooler water than normal sits off our NW coast.

When the Indian Ocean Dipole is in a negative mode, waters are warmer than usual there and provide very high rainfall for most of the country as moisture pours into the interior and feeds into the westerly belt.

Two years ago this happened, and we had rains of such a biblical nature that half the country was awash and had severe floods. Also, La Nina was pumping moisture west from the QLD side, making it a double whammy.

Heres the current picture.

Notice the blue over the top end, usually this is a positive phase of the IOD and water temps are 2 degrees cooler than usual. However, if you look at the IOD verification, its been almost neutral all winter, and now its moving slightly positive.

And you can see it’s barely positive in the forecast for the next 6 months as well. Note also, the IOD is not relevant after Spring, during summer the monsoon will run the show and the Indian Ocean will warm regardless. The IOD is important during the winter and Spring for inland rainfall.

So my theory is the cooling is seasonal, as the interior dries out with all the cold air from the south.

Heres a good graph showing why.

This is forecast for next weekend, after the front on Wednesday passes through. Behind the passage of the front the air will be very cold.

Have a look how the winds take all this cold air up through the guts of the country and then swings to the NW and out into the Indian, keeping the surface temps of the water cooler than normal. All the way to Indonesia as well.

This pattern will begin to break down over the next 6 weeks, the waters will get warm again and the flow will shift to a NW wind rather than a cold SE wind from the interior. This will begin the onslaught of moisture to begin the process of big rain events over the country.



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