Press Release – NIWA
Queen’s Birthday Weekend weather: an early winter warm-up
As we segue from autumn to winter this long holiday weekend, after the recent cold snap, it may feel more like we’re transitioning from winter to spring with the arrival of warmer air.
Let’s break things down a bit.
Strong high pressure will shift east (and actually get even stronger) of New Zealand and is forecast to be centred well east of the Dateline by Monday. Meanwhile, a trough of low pressure is forecast to move through the Tasman Sea and eventually dissipate over western New Zealand on Saturday. The two weather systems will work in unison to promote a warmer northeast to northwest wind flow. The air will flow fastest, i.e. windiest, in the Cook Strait (there’s a first!) as well as along and west of the Divide in the South Island. It’s no coincidence that the greatest threat for rain (and the greatest amounts) will occur in the same area where the moist north to northwest winds are strongest.
Notice the image below, a 24 hour rainfall forecast valid from midnight tonight to midnight Saturday, indicates that moderate to locally heavy rainfall is a good bet for much of the West Coast region, especially near and south of Greymouth. Also notice the expectation of light to moderate falls from Wellington to the Kapiti Coast. All of this results from rising motion created by the trough over the Tasman Sea and the lift induced by the briskly moving moisture-laden air hitting elevated terrain. Much farther north, over parts of Auckland and Northland, the flow will be more northeasterly, hence the eastern-facing coasts will stand the greatest chance for showers. Here, however, with the flow not nearly as strong (lower wind speed) and with greater distance from the Tasman trough, the lift, or rising air, is not nearly as great. Hence, much less rainfall.
On Sunday, the trough will continue to dissolve as it runs into much higher air pressure to the east. However, in doing so, that will be mean cloud will have the upper hand over the central and northern parts of the North Island as well as South Island areas along and west of the Divide. Along with the cloud will be the threat for scattered showers. Other areas of the country should enjoy milder and dry weather.
Looking ahead to Monday, the meteorological start of winter, low pressure is expected to take shape over the central Tasman Sea. In response, the decaying trough should be “kicked” or forced farther east so that southern and eastern sections of the North Island as well as eastern parts of the South Island will have more in the way of cloud along with the threat of a few showers. With good timing, and a bit of luck, the northern half of the North Island may have an opportunity for some sun before a new surge of cloud moves overhead in advance of the developing low over the Tasman. For the South Island, cloud and showers should have command for much of the day along and west of the Divide in response to the strengthening Tasman tempest.
As we head back to work and school on Tuesday, the storm in the Tasman is expected to intensify as it slowly moves east. This will mean a warm and likely wet start to the abbreviated work week, though it is too early to say exactly where the greatest threat for rain will be.
If you have plans this long weekend – perhaps you may be at one of the FIFA U-20 World Cup matches – here are more specific details for the main centres.
Saturday: Mostly sunny with increasing afternoon cloud. Light winds Max 16 Min 10
Sunday: Mostly cloudy with scattered showers throughout the day. Light winds Max 17 Min 13
Monday: More cloud than sun with scattered showers possible. Strengthening northerlies. Max 17 Min 14
Saturday: Mostly sunny with cloud increasing from mid-afternoon. Light winds Max 15 Min 6
Sunday: Mostly cloudy, slight chance of scattered showers. Light winds Max 16 Min 11
Monday: More cloud than sun with scattered showers possible. Strengthening northerlies. Max 16 Min 12
Saturday: Sun and cloud. Light winds. Max 15 Min 11
Sunday Mostly cloudy with chance of some scattered showers. Max 16 Min 12
Monday: Scattered showers throughout the day. Strengthening northerlies. Max 16 Min 13
Saturday: Cloudy with showers at times. Risk of a heavy shower. Moderate northwest wind 15-25 km/h. Max14 Min 9
Sunday: Sun and cloud with chance of scattered showers. Moderate northerly wind 20-35 km/h. Max 15 Min10
Monday: Mostly cloudy with a chance for late-day showers. Max 16 Min 12
Saturday: Sun and cloud. Light winds. Max 15 Min 4
Sunday: Sun and cloud. Light winds. Max 15 Min 5
Monday: Sun and cloud. Light winds. Max 16 Min 7
Saturday: Scattered morning showers giving way to a sunny afternoon. Max 12 Min 4
Sunday. Sun and cloud. Light winds. Max 13 Min 5
Monday: More cloud than sun, slight chance for a shower or two. Max 13 Min 8