Originally published Friday Sept 1 — As we do each month we take a look at the general air pressure trends and climate drivers moving in and around New Zealand, Australia, the South Pacific and the Southern Ocean.
As we head through September New Zealanders should notice an uptick in high pressure and longer dry spells. Rainfall totals should be slightly lower for many places – although may still be close to normal for some too. Despite a drier trend emerging, we’re still seeing a number of cold fronts interacting with NZ bringing some chances of rain.
Temperatures look to lean warmer than average across NZ over September and Spring by half a degree to a full degree.
September is known for being chaotic but there is some order to the chaos this month with high pressure mostly north of the Roaring Forties (Whanganui northwards) and low pressure dominating the Southern Ocean. Between the belt of highs and lows is often a westerly flow – which is likely to interact with the South Island and lower North Island more.
An El Niño “Alert” remains in place – meaning an El Niño announcement is looking more likely in the coming month.
Latest statement from the Bureau of Meteorology (BoM):
The Bureau’s El Niño Alert continues, with El Niño development likely during spring. When El Niño Alert criteria have been met in the past, an El Niño event has developed around 70% of the time.
Sea surface temperatures (SSTs) in the tropical Pacific are exceeding El Niño thresholds and have continued to warm slightly over the last fortnight. Climate models indicate further warming of the central to eastern Pacific is likely, with SSTs remaining above El Niño thresholds until at least early 2024.
The 90-day Southern Oscillation Index (SOI) is presently just below El Niño thresholds, while trade winds and Pacific cloudiness have not yet demonstrated sustained El Niño patterns. Overall, atmospheric indicators suggest the Pacific Ocean and atmosphere are not yet consistently reinforcing each other, as occurs during El Niño events.
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why should the el nino behave like a normal one the la nina didnt there was more rain in the east and south than there should of been the la nina was all over the place we only had one year out of 3 but gisborne and HB had the full monty and other odd places
At a local level, in Hawkes Bay, I have noticed a return of the old El Niño pattern where forecast rain a week out subsequently pushes out over that week with the amount of forecast rain and it’s percentage chance falling away to nothing – only six weeks ago we were well above soil field capacity and now the limiting factor to grass growth is perversely a lack of moisture – I have no doubt El Niño has arrived!