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ClimateWatch: November‘s outlook

WeatherWatch.co.nz head forecaster Philip Duncan.

New Zealand is drawing closer to the peak summer months, and WeatherWatch.co.nz we are getting closer to "La Nina likely influencing out weather patterns a little more".

WeatherWatch.co.nz says a "moderate" La Nina looks likely to impact the South Pacific and Australian weather patterns in the months ahead and November gets a taste of this with easterlies dominating and weekly rainmakers moving through the NZ area.

The South Island is looking more spring like with a few cooler southerlies in the mix but also plenty of big highs keeping eastern areas drier than usual.

WeatherWatch.co.nz says NZ's location on earth means that while we are influenced by La Nina we're also half way to Antarctica from the tropics, so the Southern Ocean storms and westerly flows can still impact NZ and this sometimes pushes La Nina weather patterns aside from time to time.

LA NINA
Scientists at Australia's Bureau of Meteorology (BoM) say there is a 70% chance of La Nina forming this summer. La Nina is when sea surface temperatures (SST) are warmer than average in the western Pacific's tropical zones. Warmer sea surfaces encourage more humidity, cloud and rainmakers into the NZ area from the north.

SST for November 1 shows La Nina developing with colder than average sea surface temperatures in the eastern Pacific (blue) compared to the warmer than average conditions in the western Pacific/NZ area (yellow/orange/red).
Credit: BoM. An "Alert" means La Nina hasn't yet formed but is likely to.
The model of models from BoM - Shows La Nina is borderline but likely to form as we head into January, then likely to ease by the time we get to Autumn.

WEATHER PATTERNS FOR NOVEMBER:

Powerful highs continue to track west to east - exiting the Indian Ocean, tracking over Australia, then the Tasman Sea and parts of NZ. We also see lows between the highs - bringing a brief window for wet weather to NZ. The Southern Ocean looks very normal for November.
Not a great deal of difference from Week 1
Week 3 looks similar to Week 1, with yet another low moving in to northern NZ. It's still a long way out, and one single low like this can stall over NZ and completely reverse long term forecasts! In saying that, the long range data suggests these lows get bulldozed away by high pressure, limiting rainfall totals in the NZ area. Another big high looks likely to come into NZ from the west for Week 4.


UPCOMING RAINFALL:

WEEK 1: RAINFALL - Departure from Normal.
Red = Drier than average. White = About normal rainfall. Blue = Wetter than usual.
Forecast Rainfall for first 16 days of November:
Very dry for the eastern South Island with perhaps as little as 1 to 5mm over the coming 16 days.
Meanwhile, the north eastern North Island could have 50 to 100mm in that same time period.
The most accurate rainfall totals for you locally can be found at www.RuralWeather.co.nz or check the hyper-local daily totals at WeatherWatch.co.nz
Green = Normal rainfall or possibly slightly above normal
White = Average
Yellow/Orange = Leaning a little drier than average
This is looking like a 'moderate' La Nina is impacting NZ over the next 3 months with slightly increased rainfall (or normal rainfall) in the areas in green. It also shows that easterly lean that matches with a La Nina set up.
 
Green = Normal rainfall or possibly slightly above normal
White = Average
Yellow/Orange = Leaning a little drier than average
Map to also include Australia showing they lean wetter this summer, except for the western half of Tasmania.
 
Green = Normal rainfall or possibly slightly above normal
White = Average
Yellow/Orange = Leaning a little drier than average
NOVEMBER
North Island leans 0.5 degrees above normal.
South Island leans 0.8 degrees above normal.
Over the next 3 months NZ leans 0.6 to 1 degree above normal.
Cloud cover and more wet weather in Aussie will pull down their temperatures by as much as -0.7 through inland NSW.

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