ClimateWatch: MARCH, Autumn & beyond (+15 Maps & extended video)

La Nina is likely near the end according to Australia’s Bureau of Meteorology (BoM), but tropical lows look likely to remain across the month of March and may still bring further rain into northern NZ and northern Australia in the coming weeks/months. It is the peak of the cyclone season after all.

However, the start of March is certainly kicking off drier in the North Island following two months of relentless storms, flooding and slips. The breather coming up will be noticeable and positive for many northern regions.

But long range, rain still looks to lean above average for the North Island and some parts of the South Island – as the lower South Island remains drier than usual.

We track big highs coming out of the Indian Ocean, south of Australia and into the NZ region, but we’re also seeing much more energy in the Southern Ocean (a classic sign of Autumn developing).

Finally, we take a look at expected rainfall in March – and the trends for Autumn compared to the trends expected at the end of winter and start of Spring later this year… this is when a possible El Nino may develop (which typically encourages more west to south west winds over NZ and more high pressure over the Tasman Sea). El Nino is certainly not locked in – but in our video we show you what the international scientific community is leaning towards with their thinking and forecasts for 2023.

ClimateWatch is brought to you by RuralWeather.co.nz (a premium WeatherWatch product) and our official business partnership with IBM.

THE MAPS….

LA NINA

Most international models in April are either neutral or showing signs of leaning towards El Nino.

BoM’s current Sea Surface Temperature anomaly map shows the excessive heat has gone from the Coral Sea and the equator has returned to normal. Note the marine heatwave around NZ and Tasmania (this is unrelated to La Nina).

The Moana Project showing there is a significant heatwave continuing around the South Island and parts of the North Island. This adds more fuel to localised downpours that linger in coastal areas and it can also help keep temperatures up a little, especially at night near the coasts. View more here: www.moanaproject.org/marine-heatwave-forecast

AIR PRESSURE... How is March shaping up high and low pressure-wise…

New Zealand is book-ended by two major storms. A powerful Severe Category 4 Tropical Cyclone near Vanuatu (JUDY) and a deep Southern Ocean storm near Antarctica (air pressure down into the 950hPa range). But a narrow area of high pressure is helping protect NZ from both of these storms (although a westerly flow in the lower South Island and some West Coast rain is likely from the Southern Ocean storm). Powerful high pressure exiting the Indian Ocean will track into NZ by Week 2, helping guide Cyclone Judy away from us.

The Southern Ocean is looking “Autumnal” with more storms and more windy weather coming into south eastern Australia and much of NZ. A sign of classic Autumn weather kicking in. However, the tropics are still active with plenty of low pressure zones, including one near Fiji.

Plenty of low pressure dropping south from the tropics to the east of NZ – but high pressure looks to move in. This may still change being two weeks out, so worth monitoring the potential for further tropical low pressure. Otherwise, this map should be encouraging for those who need a break from the rain with plenty of high pressure looking to come in from the west. The tropics will remain active for at least another two months, so just because La Nina is fading doesn’t mean we’re entirely out of the woods. March is the peak of the Cyclone Season in the South Pacific.

UPCOMING EXPECTED RAINFALL

The blues and greens around the North Island and north of NZ are at the bottom of the scale (1 to 15mm) over the next 15 days. Of course there may be some very localised downpours that push above those totals, but for the most part many North Islanders catch a bit of a break in the coming half month. Significant rain in the tropics though, with half a metre of rain expected up there in some locations. The West Coast of NZ also has the chance for over 300mm in the coming two weeks, due to more westerlies and Southern Ocean storms clipping NZ (ie, normal weather pattern for March).

A closer view. As always, to drill down deeper for the next 10 days use the rain graphs at RuralWeather.co.nz. They are powered by IBM and are the most accurate in New Zealand.

**MARCH –** Our exclusive IBM long range data suggests March may still lean wetter than average for the North Island and some of the South Island. This risk is highest in the north eastern corner of the North Island is due to the increased chance of a few thunderstorms/afternoon downpours, but also due to one of those tropical or sub-tropical lows heading southwards. The positive is that the first half of the month should be much closer to normal rainfall, possibly even below in some locations.

**MARCH, APRIL, MAY –** Little change from the March outlook.

**JULY – AUGUST – SEPTEMBER** – A new longer range product from IBM allows us to take a look at the expected rainfall in NZ for the end of winter and going into spring. It suggests the drier El Nino pattern may be settling in to NZ. This is not confirmed, but shows the current ‘best thinking’ on earth about where we’re likely to be heading over 2023.

Tax funded soil moisture map from the National Institute of Water and Atmospheric Research shows how wet the North Island is and how dry Greymouth to Westport is, and Southland. The West Coast is going to get plenty of rain in the next 2 weeks, but Southland has lower totals.

TEMPERATURES…

ClimateWatch is brought to you by RuralWeather.co.nz (a premium WeatherWatch product). We’re a small NZ company and proud to be an official IBM business partner.

Before you add a new comment, take note this story was published on 1 Mar 2023.

North Island

South Island

North Island

South Island