NZ Weather Forum

Just pop this here for future reference, a long way to go but but interesting pictures, and to be fair the GFS has done a fairly good job of predictions for the ex TCs lately as far as a week out. But probably' just for fun at this stage

Argh, to be honest the forecast isnt even worth talking about at this stage. Mainstream media is alluding to NZ is going to be hit, even though the forecast is over 1 week prognostic which is notorious for being incorrect.

So many model watchers on FB saying its going to happen and then point the source of truth at 7 day+ prognostic GFS model run, yup that makes it credible, yeah right!
Incredibly frustrating! >_

Tornado Tim wrote:Argh, to be honest the forecast isnt even worth talking about at this stage. Mainstream media is alluding to NZ is going to be hit, even though the forecast is over 1 week prognostic which is notorious for being incorrect.

So many model watchers on FB saying its going to happen and then point the source of truth at 7 day+ prognostic GFS model run, yup that makes it credible, yeah right!
Incredibly frustrating! >_

Hence the qualifications in the post above. Models have struck it lucky with last two ex TCs, so lets out of interest follow progress on this in the coming days.

Not ideal, flying out to the states on May 13 ...

Tornado Tim wrote:Argh, to be honest the forecast isnt even worth talking about at this stage. Mainstream media is alluding to NZ is going to be hit, even though the forecast is over 1 week prognostic which is notorious for being incorrect.

So many model watchers on FB saying its going to happen and then point the source of truth at 7 day+ prognostic GFS model run, yup that makes it credible, yeah right!
Incredibly frustrating! >_

Yes it is annoying and it's going to keep happening
WW does the same sometimes like with Cyclone Winston last year. If we were to raise more awareness about proper use of the models the media wouldn't listen cause they want more clicks on there websites for more ad revenue right?

WW have backed tracked..their wording is now using like lots of uncertainty wheras a couple of days ago their words were like using likely...
I think they get a bit too excited with TC's and try to be the first to make a call...so they can then claim to have exclusively called it...I think they were lucky with the last cyclone, it did what the models predicted (mind you the models came into agreement quickly..but this time they have not, and that is where you need to use your judgement and not rely on just one mode..otherwise you just model watching..and anyone can do that

Manukau heads obs wrote:WW have backed tracked..their wording is now using like lots of uncertainty wheras a couple of days ago their words were like using likely...
I think they get a bit too excited with TC's and try to be the first to make a call...so they can then claim to have exclusively called it...I think they were lucky with the last cyclone, it did what the models predicted (mind you the models came into agreement quickly..but this time they have not, and that is where you need to use your judgement and not rely on just one mode..otherwise you just model watching..and anyone can do that

I reckon it's either cause the media makes an article saying NZ could be hit 5 - 7 days + out based on one model then a lot of people ask WW what's going to happen so WW makes a prediction on it. Or WW makes a prediction with a click bait title that'll do the rounds on facebook meaning more people will tune into WW for the coming days after the initial prediction so that way WW will get more traffic to its website. Aaarrrggg it can really frustrate me, sometimes I call WW and certain media (Stuff, NZHerald) 'the super over exaggerators'

some of the models have it back on the cards for it merging with a tasman low by the end of the week
(i.e proving a moisture feed for the tasman low and energising that...this I think is a likely scenario)

Manukau heads obs wrote:some of the models have it back on the cards for it merging with a tasman low by the end of the week
(i.e proving a moisture feed for the tasman low and energising that...this I think is a likely scenario)

Yes, the ex TC is a slight complication in the forecast this week. Have to see what the 00Z model runs come up with today.

I can remember the days when weather was only a story in the media when something abnormal occured. Now our local daily (HB Today) has a weather story every day, complete with umbrellas, or ducks, or kids, whatever, telling us what to expect in the next few days.

Manukau heads obs wrote:some of the models have it back on the cards for it merging with a tasman low by the end of the week
(i.e proving a moisture feed for the tasman low and energising that...this I think is a likely scenario)

Whoa, latest GFS is showing 140 mm here on Thursday... certainly something to watch!

Yes it is now something to watch
Some of the media/FB weather forecasters need to know the basic guide of using models.

1 - 2 days out: Make predictions, compare multiple model scenarios
3 days out: Something to watch more closely
4 - 5 days out: Just something to watch
6 - 7 + days out: Why am I looking here? lol

Latest GFS (1800-07-05-2017) shows a stormy scenario but.. it'll probably flip flop.

and the BOM model is showing it too
it looks stronger overnight if you ask me

Models certainly more variable in their trends spot this system than they were worth the last two

Upper North Island will get a good soaking from an upper level trough Thursday night/early Friday and then exTC Donna passing close to East Cape later Friday.

NZstorm wrote:Upper North Island will get a good soaking from an upper level trough Thursday night/early Friday and then exTC Donna passing close to East Cape later Friday.

It will be a warmer week after a cool week last week, AK temp range today 10-20C.
Cooler flow to affect the country at the end of week.

The latest ECMWF has the ex TC coming onto upper North Island!

yes, that is what the BOM (access) model has been showing for a while now..and has it deepening as it does so, combining with the tasman low
also there looks to be another cyclone developing near samoa
(when the conditions are ripe for one, you often get another)

the media are terrible
7am TV1 breakfast:
"TC donna is intensifying and heading towards New caledonia, where the cat 5 cyclone is expected to hover over new caledonia until thursday"

Why no separate 'TC Donna' page?
I wonder if this one is the 'wolf' after all the recent 'cry wolf' storms.... no one taking seriously it seems.

^ Done...

I've been watching the models. Seems as though they are coming into better alignment over the past 24 hours and the general trend today has been for the cyclone to pass closer and closer to nz with a couple models putting a direct hit in the cards.

Something to watch!

it looks like it has moved more east ?
although that might be just it being toppled over by the jet stream..i.e the LLCC is further west of the high cloud

the cloud sheet between the 2 low centers is developing more and more...could be come heavy falls of rain for the NI

Manukau heads obs wrote:it looks like it has moved more east ?

Yes, Ensemble Mean Analysis over CMC, GFS, ECMWF, UKMO models combined has a more Eastward progression over the past 24 hours.

UKMO has more North NZ Interaction with Donna than any other model, I would classify it as an outlier at this stage, however its ensemble member output is much more concise.

Atm all numerical atmospheric model are still having problems with discerning the track from 24-48 hour+ prognostic forecast with huge discrepancies between ensemble members.

Far too much discrepancy for a call at this stage, and it seems Metservice is also reserving judgement.

Anyway it seems the parts of North Island has at least a moderate to high chance of Heavy Rain, regardless wether it comes from the ex-TC or Low from the Tasman.

Donna got her head completly lopped off last night by the jet stream
and those cloud tops have been blown off to the east
and so the true center is likely still just east of Noumea, I suggest

of more interest is baroclinic zone that has developed off Brisbane, and that one to the south of the remains of the cyclone
i.e there is alot of rain clouds building and are going to provide energy for the tasman low...