General April Weather

[Nev]

Unlike the last 2 months, April was generally a little warmer than normal. It was also fairly wet on the west coasts, particularly for Westland/Fiordland and Marlbourgh, but relatively dry elsewhere, particularly in the east.

MetService April 2024 Brief Summary - El Nino rumbles on, but a deluge from the subtropics mid-month shakes up the weather maps

New Zealand saw an El Nino-like weather picture during the month of April, as it had done through March. It also felt a lot like typical mid-autumn for the majority of New Zealand, most of the time. Large high-pressure systems brought cool mornings followed by pleasant and calm afternoons, but occasional fronts streaming up the country from the Southern Ocean injected bouts of cool air, dustings of snow about the mountain peaks, and showery spells right across the country at times.

However, this doesn’t quite tell the full story…sandwiched between this normal autumnal weather we saw an atmospheric river, a feed of warmth and moisture from the subtropics, set up across the country heralding a raft of weather watches and warnings right across New Zealand. Very heavy rain moved onto the South Island West Coast between 9-12th April, where high level stations on The Divide saw between 500-800mm widely; swollen rivers and slips ensued, cutting off numerous roads in the region. Significant amounts of rainfall reached over the Southern Alps into the Otago and Canterbury headwaters and caused major impacts, damaging a railway bridge across the Rangitata River whilst Wanaka, Dunedin and Queenstown all clocked in a top five wettest April day.

Whilst the deluge was not welcome news everywhere, thirsty soils in parts of central New Zealand were relieved to see their first heavy rainfall in months, especially in Marlborough, Nelson and Wellington. Blenheim recorded 80.6mm of rain on Fri 12th, more than their typical April’s monthly total (58.1mm).

The warm spike associated with our subtropical airmass also meant that April came in relatively near normal country-wide, despite a cooler closing salvo.

Apr 2024 Climate Anomaly Maps ℅ NIWA.png

Preliminary stats for the main centres:

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Apr 2024 Average Temps, Rainfall, Sunshine and departures from 1981-2010 normals ℅ NIWA

Site                     T-max °C      T-min °C      T-mean °C     Rain mm      Sun hrs

Auckland, Mangere       20.5  +0.1    13.0  +0.4    16.7  +0.2     77   84%    178  105%
Tauranga Aero           20.6  +0.3    11.6   0.0    16.1  +0.2     53   40%   
Hamilton Aero *         19.6  -0.5     9.2  +0.3    14.4  -0.1     62   70%    187  115%
Wellington, Kelburn     17.2  +0.5    11.2  +0.2    14.2  +0.4    105   83%    172  110%
Christchurch Aero       18.4  +1.2     5.9  -0.8    12.1  +0.2     26   46%    182  115%
Dunedin, Musselburgh    16.2  +0.8     8.3  +0.1    12.3  +0.5     35   57%    137  104%
Greymouth Aero          17.4  +0.9    10.0  +0.6    13.7  +0.8    171   85%    141  100%

* Hamilton sunshine from Ruakura

Note the 3 cooler than they should be dodgy sites on NIWA's Temp Anomaly Map - Pukekohe in South Auckland, Waipawa in Hawke's Bay and Lower Retaruke in Manawatū-Whanganui. Pukekohe in particular has been gradually unreading since about last July and is now about 2°C below what it should be.