By Philip Duncan, WeatherWatch
Our forecast for April’s weather pattern was one of “chaos” and that sure seems to be the case with thunderstorms, downpours, damaging squalls and even a tornado or two.
On top of that, much of New Zealand has had a lot of exceptionally mild airflows, especially over the North Island. Temperatures have been well above normal and this week is no different as high pressure parks itself out to our east and encourages airflow from the subtropics to spread down.
Overnight lows in some parts of the South Island this week will be in the double digits. For example in Alexandra, Central Otago, normally the middle of April would be seeing regular frosts showing up – but the overnight lows there this week will be between 10degC and 13degC and daytime highs in the low 20s.
Other parts of NZ may well have highs in the mid-20s due to the mild airflow. Southerners haven’t had as much warm weather as Northerners have had lately, but this week will put almost every region on the same page up until about Friday, when the next colder Southern Ocean change starts to arrive.
While this week feels like La Niña, we’re not in a La Niña anymore. With this month being one of chaos, as much as this week is a warmer-than-average sub-tropical week, next week is shaping up to be the opposite.
Northerly to northeasterly airflows will shift west to southwesterly and by the middle of next week much of NZ will be under a classic windier sou’wester, which looks to go nationwide.
This set-up will encourage rain to lean in to places where you’d expect – Fiordland, south Westland and the western side of the North Island. Those in the east are likely to have drier conditions and lower rainfall totals.
The chaos goes well beyond NZ’s weather. To give you an example of the Jekyll and Hyde hot tap/cold tap set-up we have in April, just look to NZ’s north and south. This week the tropics to our north are the most active they’ve been since February when Cyclone Gabrielle formed. Modelling indicates a tropical storm or cyclone is possible this week – but one update shows Queensland being hit, the next update more the Cook Islands (that’s a big difference!). Either way it shows tropical life to the north of NZ this week worth monitoring.
Next week, we may well have two storms in the Southern Ocean that brush over NZ bringing colder, windier, weather more typical with mid-autumn as we slide towards winter.
• Warmer than average this week across most, if not all, of New Zealand
• A storm in the tropics is possible. At the time of writing it posed no threat to NZ
• A change this weekend to westerlies
• Next week looks colder and windier across NZ due to Southern Ocean lows and snow on the ranges