MARCH ClimateWatch: La Nina peaks, shows signs of fading (+Video & 12 Maps)

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MARCH ClimateWatch: La Nina peaks, shows signs of fading (+Video & 12 Maps)

28/02/2022 11:53pm

> From the WeatherWatch archives

March 1 — Our ClimateWatch update for March and Autumn is now out! Big rainmakers are set to continue across eastern Australia in March while New Zealand looks at more powerful high pressure moving through.

It’s these Southern Ocean high pressure belts that have brought real variety to the South Island this summer, bringing showers, cloud and injections of cooler southerlies, but a more consistent dry pattern for northern NZ. North of this high pressure zone is a strong belt of easterly winds (between NZ and New Caledonia). It’s this large easterly flow that is feeding into eastern Australia and helping deliver a lot of heavy rain – and unfortunately more to come.

To summarise March for NZ – it looks to lean warmer than average by half a degree to 1 degree above normal. It’s also likely to lean drier than average – certainly for the first week but may well be drier than normal for the next few weeks ahead. There may be tropical rainmaker that tries to move in – but the high pressure zone over the NZ area will likely be the controlling/guiding factor for any rain this month.

WHERE ARE THE HIGHS AND LOWS PLACED THIS MARCH?
High pressure zones are still quite powerful but they do appear to get smaller and flatter as we go across this month. Likewise, low pressure zones don’t seem to be as dominant or widespread as they were in February. Still, a chance for tropical cyclones with us now being in what is historically the peak of the cyclone season for the South Pacific – but nothing major was showing up at the time we put this ClimateWatch update together.

The maps below are a snap shot on March 1 of how the month ahead may pan out. Things can still move around a bit, especially by Week 3, but it does show the likely pattern of highs and lows. To keep up to date with rainfall, temperatures, even barometric air pressure all hourly for your hyper-local part of NZ, please visit RuralWeather.co.nz.

**Today / March 1** – Low pressure lingers over New Caledonia and has the potential to even form into a Tropical Cyclone briefly this week out at sea. It’s also connected to the easterly flow driving in heavy rain to eastern Australia. Meanwhile, a powerful high pressure zone kicks off March’s first week in the New Zealand area.

**In Week two of March** that very powerful/huge high pressure zone crossing NZ lies south east of the Chatham Islands but still extends a ridge of high pressure across NZ’s two main islands. A tropical low (possibly an ex-cyclone) may be lying just north of NZ but will have a very tough job moving southwards into high pressure. Note: more low pressure and rainmakers continue along eastern Australia.

**Week 3 March –** As we get into the middle of the month and through Week 3 the high pressure zones become flatter and wider, which limits the “reach” they have (ie, they are less likely to pull down tropical air or dredge up cold Southern Ocean air giving us extreme and widespread temperature changes). It means the weather pattern may be quite lazy over parts of NZ and Australia with a few afternoon downpours inland, otherwise dry. A low in the Tasman Sea may drift into the western South Island with some heavy falls.

MARCH’S RAINFALL CHANCES:

This is a closer view of the previous rainfall map, showing NZ only. As you can see in the black boxes high pressure will keep central parts of NZ very dry. Unless an afternoon downpour develops where you are, some places through the upper South Island and even lower North Island may have minimal rainfall next two weeks ahead.

Best chances for rain may be from the north (although very borderline with the bulk of the rain falling at sea) and from a low in the Tasman Sea towards the middle of the month for the SW corner of the South Island.

LONG RANGE – RAIN ACROSS THE SEASON OF AUTUMN:

**RAIN**: IBM’s long range map suggests that Autumn may start dry but the North Island sees normal rainfall returning, while the lower South Island may be drier than usual (including rain forest Fiordland) due to consistent high pressure zones moving through. Long range guidance is just that – it’s a guide, not a set forecast.

LONG RANGE – TEMPERATURES ACROSS THE SEASON OF AUTUMN:

As we’ve seen most months over the past year, NZ leans 0.5 to 1.0C above normal for the next three months ahead (this includes any polar changes that may occur).

LA NINA:

This map shows current Sea Surface Temperatures in NZ – See more here: https://www.moanaproject.org/marine-heatwave-forecast

This animation shows the areas that above or below normal for this time of year at sea: https://www.moanaproject.org/marine-heatwave-forecast

SST (Sea Surface Temperature) Anomaly Map shows the eastern Pacific Ocean cooler at the equator (dark blue) and warmer than normal around NZ, the Tasman Sea and the western South Pacific. Classic La Nina set up. Map courtesy: NOAA

ClimateWatch is a free service produced monthly by WeatherWatch.co.nz & RuralWeather.co.nz with help from our business partners at IBM and our mates at Weatherzone.com.au.

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