ClimateWatch: OCT & SPRING – El Niño is a “hat on a hat” for NZ (Video + 18 Maps) | WeatherWatch - New Zealand's Weather Data & Alerts Authority

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ClimateWatch: OCT & SPRING – El Niño is a “hat on a hat” for NZ (Video + 18 Maps)

30/09/2023 3:00pm

> From the WeatherWatch archives

Originally published Friday PM — El Niño makes spring even more spring-like. As we go into October expect more westerly driven weather and more airflows coming from out of Australia’s desert at times. Also in the mix, colder airflows from the Southern Ocean.

Winter goes out with a blast – and that blast is the windy, unsettled, season of spring.

The spring combination including El Niño this year means windy days may be windier and warmer days hotter (mostly in eastern regions). But western and southern parts of both islands are typically cloudier, cooler and sometimes wetter in an El Niño Spring… this includes our largest city, Auckland.

El Niño is still building – and is not expected to peak until this coming January…meaning it will be peaking in summer and continuing on into Autumn next year. While NZ is in a location on earth that gets surprise rainmakers from both the tropics and the Southern Ocean, understanding that we’re only at the start of a climate driving event that lingers into Autumn of next year is a critical part of planning ahead.

It’s also important to note that El Niño isn’t a weather forecast – instead it helps drive our weather patterns across the entire Pacific Ocean over the coming months. For NZ, apart from us being very small in size land-wise, we’re also significantly influenced by weather from out of the Southern Ocean area too. This means it can be hard to be precise months in advance – but we can look at general patterns to get a better feel for what is developing or setting in across NZ weather-wise.

Our video and maps cover upcoming air pressure, temperatures, rainfall, trends and the latest sea surface temperatures around NZ, Australia and the Pacific Ocean over October and November – comparing those months with what historically has happened at this time of year over previous decades.

ClimateWatch is a monthly update tracking air pressure, temperatures, rainfall and what is driving our weather. It is not a climate change conversation. ClimateWatch is designed to help farmers, growers and those who work outdoors better plan ahead with most likely upcoming trends.

The Maps…

Top line shows Pacific Ocean: El Nino
Bottom line shows Indian Ocean: Indian Ocean Dipole (IOD)
Credit: BoM

**Week 1** kicks off on Sunday October 1 with a windy blast moving through. The map above shows the peak of that blast at the end of Saturday Sept 30. Generally speaking high pressure is tracking in a line north of NZ and low pressure over the Southern Ocean – which encourages windy westerlies for NZ and Tasmania.

**Week 2** shows high pressure dropping further south. Still a westerly flow over NZ but windiest weather moves further south of NZ.

**Week 3** shows a fairly normal El Nino set up-up for NZ, with high pressure to our north and west giving NZ fairly dry weather – but west to south west winds bring cooler air for western and southern areas and showers and weak cold fronts.

The maps above are just snap shots – in the days between changes will happen. This is not a weather forecast, but simply an outlook covering air pressure trends.

3 Maps above courtesy: Weatherzone and WeatherWatch.

Moana Project mapping – And for the first time this year there is green spreading all around NZ – indicating normal sea surface temperatures.

Pacific-wide Sea Surface Temperatures show El Nino measured at the equator where it is much warmer than usual (towards the Americas). However, it is still warmer than it should be around parts of NZ, the tropical north and eastern Australia… this has the ability to “break” the traditional dry-only El Nino pattern for our part of the world and **potentially** lift the chances of tropical, sub-tropical and mid-latitude low pressure zones bringing some rain. For that to happen, high pressure does need to break up – and the maps below show rainfall is limited over the next two weeks at least.

Western NZ has rain, especially the lower half of the South Island. A low in the first week of October will also bring rain to the south east of Australia.

Spring and El Nino westerlies encourage wetter weather in western NZ and drier in the east. Being spring it’s still going to be unsettled and colder at times with this wet weather.

Longer range over October and much of NZ leans drier – with northern areas more exposed to drier high pressure. Leaning drier doesn’t mean every day is dry – sometimes it can be frequently showery, but weekly totals start to drop below normal.
Longe range data via: IBM / WeatherWatch.

By November northern and eastern areas look to be leaner drier than usual – still rain coming into the south west, and some of that will go further up NZ. It’s likely by November we’ll know which parts of NZ are facing an especially dry summer. For now, spring still has silver linings rain-wise.
Longe range data via: IBM / WeatherWatch.

A healthy set-up nationwide soil moisture-wise going into October. Map credit: New Zealand taxpayers & the National Institute of Water and Atmospheric research.

Satellite data showing liquid moisture within the top 2 metres of the soil. Credit: US Government.

NZ leans 0.3 to 1c above normal nationwide. 0.3 around Southland and 1c more likely round Bay of Plenty, Hawke’s Bay and Gisborne. Australia leans over 2c above normal inland for some areas. Longe range data via: IBM / WeatherWatch.

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Comments

Before you add a new comment, take note this story was published on 30 Sep 2023.

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Peter Thomas Langer on 29/09/2023 12:55pm

it all depends how the tropics behave during el nino not all el ninos are dry not all la ninas are wet i have seen some dry la ninas

Reply

Marcus Adam on 29/09/2023 1:44am

Appreciate the very well presented and informative forecasting .
Also great to see Wairoa showing up on the weather maps !
I wonder why ?
cheers

Reply

WW Forecast Team on 29/09/2023 2:15am

Thank you very much for the feedback, it’s appreciated.
The maps auto-select locations and sometimes it picks smaller places (like Te Kuiti instead of Hamilton, or Geelong instead of Melbourne). But my Dad is from Wairoa, and my late grandparents – so I love seeing it! 🙂
Phil D

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