ClimateWatch: MAY & how June, July are shaping up (+Video & 13 Maps)

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ClimateWatch: MAY & how June, July are shaping up (+Video & 13 Maps)

1/05/2023 3:36am

We’re officially in an El Nino ‘Watch’ as conditions continue to build across the equatorial Pacific in favour of this climate driver. While La Nina brings humid nor’easters to NZ, El Nino tends to bring the opposite – cooler and drier sou’westers.

We’re currently in a “Neutral” phase (although it does still feel like La Nina in New Zealand due to the sub-tropical winds in the first week or so of May – and the last couple weeks of April).

“Neutral” means more chaos and no set pattern to drive our weather here in New Zealand. Over the months ahead it looks as though El Nino will build and this should start to slow down the number of sub-tropical rainmakers NZ gets. It is worth noting that NZ’s small size means one big low or high can upset any long range forecasts, but generally speaking May looks unsettled and chaotic to begin.

June and July may start to be a bit more westerly driven, rather than nor’east driven (much of our weather has been north to north east driven over the past month).

Colder air is definitely growing south of NZ and Australia’s south eastern corner is getting plenty of tastes of this. NZ, for now, is on the warmer side of the Tasman Sea (weather-wise) so we’re not getting the same wintry southerlies. That cold air is just south of NZ so be prepared at anytime for it to pounce on us! But, for the start of May at least, our weather remains milder thanks to sub-tropical airflows and northerly quarter winds.

The Maps…

CLIMATE DRIVER

El Nino Watch now in force – meaning El Nino is likely building. Credit: BoM

BoM’s model of all models showing the conditions for El Nino becoming stronger as we head into late winter/early spring.

All global models (except NZ, due to Niwa’s commercialism) show a clear trend … El Nino later this year looks to be much stronger than the La Nina was at the start of the year. Credit: BoM

AIR PRESSURE IN MAY…

WEEK 1 – Kicks off just like April did, with plenty of high pressure around NZ but also low pressure bringing sub-tropical winds. The first week of May will be much warmer than usual, wetter and windier thanks mostly to the very powerful (and tall – ie, north/south) high pressure zone to NZ’s east. It’s this powerful high, in tandem with the weaker Tasman Sea low, which are bringing the wind, rain and sub-tropical warmth to NZ for the first full week of May.

WEEK 2 – By the Monday in Week 2 the low pressure zone from Week 1 will still be moving through , coupled with extra low pressure coming from the Tasman Sea area. It doesn’t look as dramatic as week 1, but still the possibility for warmer than average weather, downpours and maybe thunder.

**WEEK 3** – You can feel the breath of relief looking at the huge settling high pressure zone. This high may bring an extended settled spell (provided no Southern Ocean storms come up and try to tear it in half). For now it looks to bring a much more settled period into the second half of the month compared to the first half. Modelling via: GFS.

UPCOMING RAIN…

Most of this rain will fall in the first 8 days of May.

Long range data from IBM/WeatherWatch.co.nz shows May’s heavy rain may be balanced out by a drier June and July. Of course, it only takes one stubborn high or low to break a long range forecast in a country as small as New Zealand, but the longe range best thinking shows an uptick in drier weather for NZ once we get into winter (compared to average). We’ll have more details in our June update, but for now May looks to start of wetter than average in the north and west of NZ, then a drier pattern kicks in going into winter. Being in a “neutral” zone right now it’s harder to be more precise going out long range with no ‘predictable’ pattern likely to dominate (as opposed to La Nina and El Nino which tend to make more repetitive weather set-ups).

NIWA’s soil map is delayed by them for 24 hours for their own commercial reasons, so this map doesn’t take into account rain that fell on May 1. (Niwa is a Government Agency but is very commercial these days). This soil moisture map should look a lot “bluer” in the North Island and western South Island by the second week of May, but the eastern and southern South Island may not change much, or will get drier.

No surprises here – NZ continues to lean warmer than average going into winter 2023. In April many places were over 2 degrees above normal overall, which is quite a lot. Next three months ahead looks 0.5 to 1C above normal for most NZ regions.

If you want to go for a swim in the sea, conditions are still quite pleasant in the North Island. Much cooler around Dunedin though!
Credit: Moana Project

Marine/coastal parts of NZ still remain warmer than average. Data courtesy / Moana Project.

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Greg on 1/05/2023 8:50pm

Philip & crew, you are a sane ‘voice in the wilderness’ of climate cacology, ie. NIWA & other govt Cyclone Season den!ers – you are the only meteorologists to correctly refer to ex-cyclone Hale and ex-cyclone Gabrielle, both of which were downgraded two days before arriving in NZ waters, while RNZ etc still continue their bs dis/mis-information.

Cheers, keep it up, Greg.

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WW Forecast Team on 3/05/2023 6:59am

Hi Greg,
Thank you very much, really appreciate the kind support for our small team!
Cheers WW Team

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Andy on 1/05/2023 7:07am

What great article.

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WW Forecast Team on 3/05/2023 7:00am

Many thanks, Andy 🙂
– WW

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