ClimateWatch: Mixture of pattern & chaos in DEC & SUMMER outlook (Video + 13 Maps)

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ClimateWatch: Mixture of pattern & chaos in DEC & SUMMER outlook (Video + 13 Maps)

3/12/2023 6:50am

Originally Published Nov 29 — El Nino peaks in December and January, just in time for the hottest part of summer. Our final ClimateWatch for 2023 focuses on pattern and chaos.

We can see more high pressure belts and drier areas setting in…but the chaos factor (mostly fuelled by warmer than average air and sea temperatures in many places away from NZ) means we have more chances of rain than we usually would in an El Nino Summer.

For most this is a positive.

Long range data isn’t perfect at all – but the data we use is the most accurate on earth. It’s helpful at painting a general big picture of highs and lows and where they are trending and what that means for rainfall and temperatures. For NZ we’re small in the big scheme of things – we can always buck the international trend. But our latest data backs up what we saw earlier this year – that spring would be more spring-like and Summer has higher chances of drying out for the eastern and inland parts of NZ, in particular the North Island and upper South Island.

For the most part NZ leans drier in the North Island once we get to January…but December may still see a few rainmakers into the wet east (southerlies do that, so too do easterlies).

Generally speaking it’s a positive forecast for NZ’s growers and farmers…but worth noting the main concern for dry weather looks to be building over the next 3 months around the North Island and upper South Island.

We’ll continue to monitor this and if anything big changes in December we’ll let you know with a news story and big headline. We’re about giving you the best data we have at the time – but we’re not magic and can’t lock in 2024’s weather. We provide these long range forecasts out of demand, rather than us having the silver bullet answer. So we use the most accurate forecast data on earth plus then put our finger on the pulse of local weather patterns (chaos factor) and try to build that Big Picture for you from that.

Have a great start to summer – our next ClimateWatch Video will be in 8 weeks time (Jan 31/Feb 1) and our news content doesn’t stop over summer on both our websites.

RuralWeather.co.nz / WeatherWatch.co.nz

THE MAPS…

AIR PRESSURE IN DECEMBER

**WEEK 1** kicks off with high pressure over NZ but a low from Australia coming in… this low will fall apart over NZ in the first weekend of December bringing heavy West Coast rain (100mm+) and showers to the western and upper North Island. It’s possible this system will also bring some rain into eastern Bay of Plenty and East Cape in the first week of December.

**WEEK 2** (Dec 8) kicks off with a low south east of Dunedin, this may initially encourage westerlies but they may turn southerly (and this can bring in some wet weather again to eastern NZ). A tropical low near Vanuatu is trying to form into a cyclone. A narrow but significant block of ‘El Nino high pressure’ to NZ’s north looks, for now anyway, to protect NZ.

**WEEK 3** (Dec 15 going towards the last week of Dec) A mixture of pattern and chaos. The pattern? The stream of high pressure zones in red moving from west to east. The chaos? The low pressure zones in blue over central Australia bringing thunderstorms and downpours, the tropical depression north of Fiji which may become a storm if it wasn’t for the nearby blocks of El Nino High Pressure – and there’s also a low around the Cook Islands.

EL NINO…

Global pattern peaks in Dec/Jan. Credit: BoM

Nothing to see here! For the first time in 2023 there is NO marine heatwave anywhere in Aotearoa New Zealand.

Soil Moisture Map from the NZ Taxpayer shows something most wouldn’t expect in El Nino – the eastern North Island is saturated. There will still be more wet weather in the eastern North Island this December – but we do expect those rainfall totals to start to drop and larger dry areas to increasingly form.

THE BIG PICTURE…

RAINFALL

February is peak heat usually – but can also be more humid. This may be the case for Australia with thunderstorms and widespread showers. For NZ it may be a case of more westerlies (this far out it’s a bit hard to nail the specific causes for the rain/dry).
*Data Exclusive to WeatherWatch/IBM.*

**3 MONTH – RAINFALL – DEPARTURE FROM NORMAL (DEC, JAN, FEB)**
*Data Exclusive to WeatherWatch/IBM.*

**3 MONTH – RAINFALL – DEPARTURE FROM NORMAL (JAN, FEB, MAR)**
*Data Exclusive to WeatherWatch/IBM.*

**3 MONTH – TEMPERATURES – DEPARTURE FROM NORMAL (DEC, JAN, FEB)**. Showing the big picture as NZ is always in the yellow (leaning 0.5 to 1.5c warmer than usual). This global picture shows the data isn’t broken, with parts of the world leaning cooler. But it also highlights how, compared to the previous 30 or 40 years, many places are experiencing an uptick in general temperatures by 0.5 to 2 degrees. *Data Exclusive to WeatherWatch/IBM.*

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