This El Niño Is Not Like The Others
The weather report: Storms, heavy downpours, cooler weather.
The weather forecast: Storms, heavy downpours, cooler weather.
After a hot and dry start to spring, the south-east of the country has since settled back into a cooler, wetter pattern, while at the same time the west has baked under record heat.
It's not quite the El Niño we were expecting.
For East Coasters, it's a lesson that not all El Niño's equate to howling north-easters, and relentless inland heat.
In fact, of the two, La Niña has a greater and more predictable influence across the country. This is due to the close proximity of La Nina's main driver. Namely, warmer than normal sea surface temperatures. The warm water pools to the north of the country, resulting in cool and moist easterly winds, increased rainfall, and more swell activity from the east.
The warm water also produces lower pressure which then shifts the sub-tropical high-pressure belt further south during summer and autumn.
During El Niño, the driving forces operate at arm's length from Australia; the warm water signal sitting way out in the central and eastern Pacific. This is why El Niño's don't always play a major predictable factor in the weather and swell climate for the country. Conversely, it's why El Niño is more prominent in America.
Generally speaking though, during El Niño rising air in the central/eastern Pacific travels back to the west and descends across the Indonesian region, leading to suppressed tropical activity and less moisture for the country. Cooler waters developing off Indonesia also enhance this moisture deficit, bringing drier, warmer weather to Australia.
But when we take a look at the current sea surface temperatures around Australia we can see why this El Niño is wetter than expected.
Apart from the Coral Sea, sea surface temperatures are higher than normal for this time of year (warm anomalies), and we've even got marine heatwave conditions forming in the Tasman Sea.
The Indian Ocean Dipole - which caused cooler water off Indonesia - was a strong event yet it focussed a little further west and not immediately off eastern Indonesia. This has seen water temps rise immediately north-west of the country.
To show how this El Niño differs from others, let's compare the current sea surface temperature anomalies to the last time we had a combination of strong El Niño and positive IOD. That was the 1997/1998 event.
First, I’ve plotted the sea surface temperature anomalies for October 1997, and below that the sea surface temperature anomalies for October 2023.
What stands out is the amount of extra heat in the oceans between each event, spaced two and a half decades apart.. The classic warm El Niño tongue through the Pacific Ocean is clearly evident in both images, yet in the second it doesn't stand out as much; there are many regions of warm water.
So far, the 2023 El Niño signal isn’t as strong as it was in 1997, and to make this clearer, the third image below is the difference between 1997 and 2023.
The warm temperature signature throughout the western North and South Pacific is significant, as is the warm pool sitting directly offshore around the north-west and south-east of Australia. You can also see the warm pool through the central and eastern Pacific is weaker (not as warm) this year compared to the 1997 event.
The warm sea surface temperatures surrounding Australia are the sources for a more saturated atmosphere, hence the persistent troughiness and instability across the southern states.
This is preventing high pressure from setting up camp in the Tasman Sea. The result so far has been pulses of fun, close-range swell without any persistent, embedded north-east wind.
Not a classic El Niño by any means and it looks to persist into the coming summer months.
On a final note, the North Pacific season is still looking healthy, with the warm anomailes sitting east of Japan fuelling any storms that spawn in the region.