Daniel Corbett, resident forecaster and meteorologist for 1News, explains what to expect as we head into the new season.
As we move into spring this week all the talk around the globe is about the growing El Niño. It still has the potential to be very strong and impactful. Some will call it super but after we look back at the significant and potentially devasting weather it could bring around the globe, “super” might not be the best adjective.
So, what is talk about and how is it really going our affect our plans through spring?
Once again, it all starts with sea temperatures, not around New Zealand, but a long way away in the eastern Pacific. The past several months has seen seas in the eastern equatorial Pacific warm rapidly - almost as if you put the neighbourhood swimming pool heater on max heat and then left it on for several months.
Some of these seas in the eastern Pacific are 3-5 Celsius warmer than normal. Heading off the current scales of measurement!
This is the opposite of where we were back in 2022-23 when the seas were much cooler. Back then we had significant rain makers affecting the north of the country.
The easiest way to understand how the change in sea temperature can impact the weather is to think of the rising steam from a hot bathtub. Think of the steam as increasing rising air or vertical motion in the atmosphere that can help to more readily grow clouds and storms.
So, in other words, the warmer seas become more favourable for rising motion, more lift and then lower pressure. It is the opposite with cold seas - the air moves down and high pressure grows.
Not like 2022-23
In El Niño events, low pressure increases in the central and eastern Pacific creating more rain and storms here. In La Niña, the Low pressure was north of New Zealand back in 2022-23 - hence all the rainmakers.
This spring and summer could be quite different.
A quick look at the sea temperature anomaly map shows a lot of red lately (warmer than normal seas) much more than blue areas (cooler seas) these days.
The El Niño has been growing over the past several months but has yet to really affect our weather because in our winter the cold and active storms from the Southern Ocean kept us busy.
Now that we are in spring, we start to experience the global seasonal shift as the tilt of the earth helps bring about the shift in the direct sun position back into the southern hemisphere.
Our days get longer and the ribbon of wind that spreads around the globe at higher level in the atmosphere, the jetstream, shifts south. This starts to reduce the impact from the Southern Ocean's active weather and instead the drivers come in from further north where El Niño is bubbling to life in a big way.
What it means for our spring weather
Well spring will start much like any other with the typical rollercoaster ride of weather. One day will be wet and windy, the next day could be fine. Sprinkle in the odd colder surge as the last bits of deep Southern Ocean air try and make in roads across the country.
The thing to notice as the weeks press on will be the areas of high pressure - the spells of fine weather. They will start to grow from the northwest and become more prevalent through late October and November to our north.
The passing fronts will start to thin a bit and general wind flow will be more from the west. We will start to see more of the typical El Niño westerlies. That means a general westerly wind with passing fronts dropping most of their rain in western parts of the country. Less so further east.
The winds could be quite gusty at times as fronts pass by, especially in those prone places like Cook Strait - watch out, Wellington.
This, with the help of our well know foehn effect, will help push the mercury well into the 20s in the coming months. This will also start to dry things out in the east. The ground and soil moisture is at a good point right now, but several weeks of warm dry winds can quickly change that.
Farmers will no doubt be monitoring their moisture levels for potential issues going into the summer. Drought could even become an issue in some areas.
One wild card to be aware of, we always have them these days with the long-term planetary warming, is sudden extreme weather from slow moving or cut-off lows.
These can sit for a half day or so and squeeze out the copious amounts of moisture in the atmosphere in a short period of time, leading to extreme rainfall events. While these can happen almost anywhere, it's worth noting the east where they could have an impact on the potential drying trend of the next several months.
So, in a nutshell, enjoy the spring - it could be a warm one for some, breezy for others.
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