ClimateWatch: APRIL is looking “chaotic”, but fairly normal (+Video & 13 Maps)

La Nina is gone and now we’re in a NEUTRAL period. That basically means Autumn is Autumn, without any major climate driver changing things.

Over the coming month New Zealand and Australia are both likely to receive a mixture of big highs and low pressure zones, providing that classic mid-Autumn-set-up where we have dry/warm/settled weather for a time, then a burst of wind/cold/rain and snow on the ranges. Put simply, it’s summer slowly fading and hints of winter now arriving.

Rainfall looks to be normal or even below normal generally speaking. This may be due to some slow and large highs tracking over the country. But normal rainfall means most places will get wet weather at some point and we do see a number of lows from the south, west, north and east (yes, all around us) which may bring wet weather at some point. As always, there is the chance of localised flooding – but the general forecast suggests rain-bands will be broken up (even within regions).

With La Nina gone the tropics do look quieter – but the sub-tropics (basically the zone north of NZ but south of New Caledonia and Fiji) – looks to be active with a few lows which could brush northern NZ and even eastern regions down to the South Island.

Temperatures look closer to normal than they’ve been in months – but the scales do still tip slightly warmer than average for all regions. (Doesn’t mean every day is warm, but it means frosts and cold days or cold nights may be reduced compared to previous decades).

In true Autumn style for NZ there is real variety and a messiness to the upcoming pattern, which sees plenty of dry and settled days mixed in with “oh yeah, summer is definitely now over” type weather!

CLIMATE…

La Nina is gone – now we’re in NEUTRAL, but there is an El Nino WATCH in place…basically this means “the data aligns with a likely El Nino event later this year”. El Nino is the opposite to La Nina and for New Zealand it means more west to south west winds and likely more high pressure zones in the Tasman Sea. El Nino events are often windier and drier for many regions compared to La Nina, with cooler sea surface temperatures here. (BoM graphic)

A moderate chance of El Nino forming by late winter or early Spring (BoM graphic).

The model of all international models (excluding NIWA which is too commercialised to share NZ public data) shows a clear trend into the El Nino phase later this year. It’s not yet locked in – confidence according to Australia’s Bureau of Meteorology (BoM) is “moderate”.

We trust BoM for Climate guidance as BoM still operates as a truly public-good service, like all other modern nations – unlike NZ’s *NIWA*, which has now sadly become aggressively commercial, despite being a public agency. That is why we cannot include NIWA data in our ClimateWatch updates.

Current Sea Surface Temperatures: www.moanaproject.org/marine-heatwave-forecast

Current Sea Surface Temperature ANOMALY map – basically, how much warmer or cooler than average for this time of year are our beaches and marine areas: http://www.moanaproject.org/marine-heatwave-forecast

HOW APRIL IS SHAPING UP AIR PRESSURE-WISE (ie, where are the highs and lows)…

The first week of April sees the colder southerly of late March fading and incoming high pressure. Still a few showers this week – and rain on the West Coast – but generally high pressure moving in.

Low pressure is forming over Easter Weekend north and west of NZ and by Monday April 10 it will be starting to engulf NZ with areas of rain and showers – but milder for many too. The next big powerful high is coming in from the Indian Ocean to Western Australia but won’t likely impact NZ until the end of April.

By Week 3 that next big high pressure zone from Australia (which in Week 2 was over the Indian Ocean) moves closer to NZ. However, before it arrives a low pressure zone from the Sub-tropics may well drop past to NZ’s east … or, it may more directly hit the North Island. ClimateWatch is more about the trends than it is a specific forecast – so we go back to our word to describe April as “chaotic”… still the risk of localised flooding, but there’s a lot of variety with our highs and lows this month. Generally speaking, most of the excessive rain at this stage looks to be at sea, so NZ’s rainfall looks to be around normal (again, generally speaking).

RAINFALL…

The 7 days from April 3 to April 10 look to be drier than average for most places, or closer to normal.

Long range and NZ leans normal to slightly drier than normal for most regions – but the coastal sides of Canterbury and Marlborough are perhaps a little wetter (but, this map will also take into account rain that has fallen over the past few days with the colder southerly from late March and very early April).

If you look at the Key/Legend, you’ll notice the wet and dry are close to normal (ie, we’re not seeing extreme red or blue, we’re seeing yellows/golds and light greens which are all around the normal mark). Localised flooding is always possible beyond this map, if a low moves closer or if a downpour forms somewhere and stalls – so always keep up to date with weekly forecasts and MetService warnings and watches if rainfall matters to you.

Current Soil Moisture conditions. NIWA is 100% tax owned Crown/Government Agency.

TEMPERATURES…

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