NZ Weather Forum

Looking like warm NW conditions across the country with a front somewhere, possibly upper South Island.

Means salads better than hot winter food in such hot weather

Yes, generally dry/warm Xmas day for NZ, Rain for the WestCoast from a weakening Front, trend post Xmas is for dry warm weather, main rain threat mostly to the far SW of NZ.

WW forecast now out: http://www.weatherwatch.co.nz/content/y ... y-forecast

But I have issues with it, like what on earth are they looking at to get this idea?! Neither the GFS, the UKMO nor the ECMWF have a "deep low forming in the Tasman Sea around Monday and affecting New Zealand on Wednesday and Thursday".
The pattern looks to be a Tasman Sea high that moves off to our east and becomes stationary there. All models are hinting at this, and no sign of a deep Tasman Sea low. There is a shallow trough forming in the north Tasman that gets weakened even more by the strong upper ridging before having a significant impact on NZ, and a low in the southern Ocean, but nothing deep anywhere.

So where does this come from?

It means the forecasts look way off already:

Auckland Looking cloudy but dry with sou' west breezes and temps in the low 20s. - Actually it looks like northeasterly.

Hamilton Not too much wind and quite overcast with around 23/24 degrees expected. - Hamilton doesn't get much wind anyway so this doesn't say much.

Tauranga Long sunny spells and a breezy westerly is likely. Top temperature is around 23. - Westerly? No, onshore northerly if anything.

Wellington Northerly winds picking up but some sunshine with passing clouds. Low 20s. - Wellington is northerly almost always, so hard to argue with this one!

Christchurch A dry morning, risk of a shower later. Nor' easters. 23 or 24 is possible. - The lee trough looks offshore, so northwest is more likely.

Dunedin A few showers are possibly with an easterly breeze. Temps around 20/21. - Looks like northeast for them and westerly for Invercargill.

Of course it's all up in the air because it's a long way out, but the point is these forecasts do not coincide with current model guidance.

http://www.weatherzone.com.au/models/

but I would not trust this far out of a tasman low and showery NE winds changing SW
maybe if it was a la nina

I go for N or NE winds over the NI at least on xmas day

Manukau heads observer wrote:http://www.weatherzone.com.au/models/

but I would not trust this far out of a tasman low and showery NE winds changing SW
maybe if it was a la nina

I go for N or NE winds over the NI at least on xmas day

That's an old run. The latest run is not like that, and the ECMWF and UKMO never went with it. So I suppose the forecasts are consistent if by "latest computer models" they mean "an old run of one model"!

I think weak upper level tough for the NI from tuesday, NE moisture feed = showers mostly for upper NI and over the high country ( afternoons) hopefully clearing by Xmas day. I see the recent ECMWF run has a decent upper level feature west of the NI on the 26th, see if it is still there in tonights run

yes, there could be a weak easterly surge or at least trade wind type showers

I like Rain on Xmas day it gives the mood like 1996.

It's not on the newest ECMWF or GFS. An important part of long range forecasting is checking the consistency of a model, not just grabbing the newest run and "running with it" regardless of how crazy it may be. The GFS 12Z run was at odds with itself and other global models.

I don't tend to take models too seriously beyond 72hrs. Obviously they can go through big changes.

going on past experiences,
a new high with a SE then easterly change after a cold front will mean showers/rain areas to come back on the easterly for the auckland/northland area
the key will be a steady SSW wind (pressure wind) with a fast rising barometer after the cold front, to hearald in the new high

Hope the 1st scenario Brian,overcast either calm or a really good NE with frontal rain on Xmas day,its easier than the heat,the heat can come for new year.

Last night's ECMWF and MetVUW's GFS plots look remarkably similar for midday on Xmas day.

I also think that while more inland areas of the eastern SI may the get NW'er's, more coastal centres like Chch may still be subject to more typical NE'ers?

Thought it might be worth recording those plots here to compare with conditions on the actual day.

We go on data provided partially by GFS and more detailed, accurate data, from our contacts at the Weather Channel - who provide an incredibly scientific and accurate grid-style formula of forecasting across NZ.

We never promote our long range forecasts as being highly accurate - basically they are a commentary on what the computers are saying - and we always suggest checking back closer to the time for the "truly accurate" picture. It's not just the people in this forum who care about long range forecasts and discussion of potential systems... we get bombarded by emails from the public wanting to know what Christmas Day will be like weeks in advance.

You're right - they do change - but I'm sure forecasters wouldn't produce these long range maps/data at all if they were completely worthless.

That low, in the Tasman, was showing up in our northern weather stations data for a couple of days, then co-incided with the GFS run. Still looking very unstable next week off the Aussie coast but certainly the high looks dominate now.

By the way - just sharing this info with the forum. I know we have a mixture of supporters and ...well...non supporters in here!

Myself wrote:It's not on the newest ECMWF or GFS. An important part of long range forecasting is checking the consistency of a model, not just grabbing the newest run and "running with it" regardless of how crazy it may be. The GFS 12Z run was at odds with itself and other global models.

You're crazy for suggesting that we would even do that - we would never use a single model and "run with it". We compare all model runs with computer data and usually over a 48 hour period.

Looking good for much of the country, except maybe the West Coast.

The high for xmas day was 27 yesterday, now 24 say Metservice. Blue skies going for 31. Quite different. Hopefully the latter.

GFS model has backed off the 850 temps a bit.
Probably still go for high 20s for inland Canty.

For the Canterbury region I'm going for a fairly cloudy day with odd bright spells ,humid at times towards the afternoon,possible drizzle on the coasts and inland ranges and northern parts during the afternoon turning to light rain later mainly about Kaikoura Ranges in the North.Temps a high of 26c with a light North Easterly turning North Westerly during the afternoon.

Karshvardidgâh wrote:For the Canterbury region I'm going for a fairly cloudy day with odd bright spells ,humid at times towards the afternoon,possible drizzle on the coasts and inland ranges and northern parts during the afternoon turning to light rain later mainly about Kaikoura Ranges in the North.Temps a high of 26c with a light North Easterly turning North Westerly during the afternoon.

Upper level NW winds from early in the day will insure that there will be no low cloud or any drizzle on the coasts, especially inland which should revive an early wind from the NW,temps inland will lower because of this wind.
I'm picking the MS should have stuck with original high of 27C for CHCH,even though the NW may not get there till later in the day

Well i do think its going to be in the high 20s Today (Christmas day) bring it on! and MERRY CHRISTMAS to everyone on the forum hope you all have a fantastic day and drink heaps, eat lots
If there was a thunderstorm chance this afternoon id still be out chasing it with any others! just not around lunch
Have a good one guys!

valley fog here this morning.....like our own xmas snow
not a cloud in the sky !

Yes, amazing blue dome xmas morning here, light southerly breeze at the moment and almost 18 degrees already, going to be a warm one

I reckon its got to be the nicest xmas day weather I can remember