ClimateWatch for December & rest of Summer (Jan/Feb) +13 Maps & 15min Video

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ClimateWatch for December & rest of Summer (Jan/Feb) +13 Maps & 15min Video

2/12/2020 4:00am

> From the WeatherWatch archives

La Nina is a no show for the start of December in New Zealand with an aggressive spring-like westerly returning. Why? Because the Southern Ocean is stormier than usual and La Nina is only moderately strong.

In fact La Nina is likely to peak in December and January before easing into 2021. As WeatherWatch.co.nz has been exclusively saying for months now, this moderate strength La Nina, which is measured at the equator, may not have the impact news outlets and Government forecasters are headlining.

Instead, the first two weeks of December will be heavily dominated by strong westerlies, Southern Ocean storms and western rain. Northern NZ will be closer to high pressure – with a powerful belt of high pressure between NZ and the tropics basically stopping La Nina weather patterns in our part of the world.

But it doesn’t last this way.

By mid-December there are some signs of sub-tropical and tropical life and possibly a sub-tropical low bringing in rain to northern NZ.

Long range the data from IBM does suggest wetter weather will come in to northern NZ over December and January.

Temperatures – generally speaking – look to be at least 1 degree above normal for December and January and maybe 0.5 to 1 degree above normal for February.

Our next ClimateWatch VIDEO update will be issued at the end of January but we will have a ClimateWatch NEWS update on December 31 at WeatherWatch.co.nz and www.RuralWeather.co.nz.

THE MAPS:

Credit: Australia’s Bureau of Meteorology (BoM)

La Nina isn’t very strong this time around, peaking in December and easing further in January back to “Neutral” by April. Credit: Australia’s BoM

Soil Temps 10cm down: Basically NZ is into double digit soil temps everywhere with late teens and early 20s now further to the north. Credit / IBM

Tax funded soil moisture maps, by the National Institute of Water and Atmospheric Research (NIWA) — a 100% Government Owned Crown Research Institute.

FORECAST RAINFALL….

December’s rainfall in the first week of December COMPARED TO NORMAL.
Red = Drier than usual, White = Normal rainfall, Blue – Wetter than usual.

The large pale blue shading north of NZ is a sign of extra high pressure – and not what you’d expect to see in a La Nina set up.

Rainfall perhaps returning to northern NZ.

THE AIR PRESSURE SET UP…Tracking the highs and lows into most of December…

Red Boxes = High pressure areas. Blue Boxes = Low pressure zones (GFS)

Yet another storm in the Southern Ocean affecting NZ – but sub-tropical nor’westers possible in the upper North Island.

Perhaps a bit more La-Nina-like with a low in the upper North Island (not locked in this far out) and more lows forming to the north of Aussie. Highs from Aussie starting to track further south and into the South Island.

LONG RANGE FOR ALL OF SUMMER (DEC, JAN, FEB)

**Temperatures** – Leaning about 1 degree above normal, maybe more, nationwide for **Dec, Jan and Feb.**

**December’s** **Rainfall** **Departure from Normal**– showing the north is leaning wetter than usual (by maybe 50mm) while the south is the opposite, possibly below average by 50mm. This is looking more like La Nina and suggests that the spring-pattern that starts December, may not end December.

**Rainfal**l **– Departure from Normal – Dec, Jan, Feb:** First time this year we’ve seen blue in the upper North Island. This indicates La Nina rainmakers will push into the north of NZ over the summer months, helping to balance our water deficits.

ACCURACY
The accuracy in the three maps above from IBM/WW are is about 65%. This is the most accurate long range data for NZ, but it’s not perfect.

It’s a helpful guide to roughly see if rain may be returning or not. While La Nina isn’t overly powerful for NZ this year the warmer sea surface temperatures are with us. Once high pressure from northern NZ and north of NZ finally breaks up and clears there is a significantly increased chance of sub-tropical lows and rainmakers developing.

NEXT CLIMATE DRIVER UPDATES
– Our next ClimateWatch Video will be issued in two months time, in late January
– Our next ClimateWatch News update will be issued, with full maps, on December 31

Comments

Before you add a new comment, take note this story was published on 2 Dec 2020.

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Anna Ta on 4/12/2020 6:27am

Helpful forecast, thanks. Much appreciated.

It is surprising to see you surprised that summer will be one degree warmer than average – isn’t this consistent with models of anthropogenic climate change?

The “climate” forecast is extremely helpful, thanks for all your work

Reply

WW Forecast Team on 4/12/2020 6:11pm

Thanks for the comment and kind feedback :). We’re surprised because it doesn’t just automatically apply to the whole country each and every month (the extra 1 degree). NZ’s location on earth means we get some good injections of cooler air too which can somewhat regulate our temperatures. But yes, you’re right – probably should be so surprised really.
Cheers
Phil D

Reply

Bryan Norton on 1/12/2020 5:38pm

Thanks for the useful maps & insights.

Reply

WW Forecast Team on 1/12/2020 6:30pm

Cheers Bryan, thanks for the kind feedback.
Phil D

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Peter Thomas Langer on 1/12/2020 4:01am

yeah well if it was a real la nina the places below taupo would be in danger of drought

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