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Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Wed 21/11/2018 17:11
by snowchaser01
Yet another low set to bring some potentially dramatic weather to NZ this weekend and the first half of next week.
Rain and strong winds to affect the North Island this weekend, before easterlies and rain for much of Canterbury on Sunday, Monday and Tuesday! Could be interesting. Thoughts everyone?
EDIT: Forgot to say, Metservice have mentioned the above in their Severe Weather Outlook this afternoon.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Wed 21/11/2018 20:56
by NZstorm
Eu has a subtropical moisture feed reaching east of the South Island on Monday. Looks like there will be a cut off low in the eastern Tasman.
Precipitable water chart for Monday.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Wed 21/11/2018 20:59
by Cyclone Tracy
Nice one Stormchaser, yes it’s an incredibly complex beast and has started to spin off South Australia driven by significant upper cold core cyclone. It's then going to spawn a second surface circulation off the NE coast of Tassie by tomorrow night, which then cuts off from the westerly flow while under going bombogenesis. UKMet showing near 970 hPa on Friday off the SE coast of OZ.
I’m going to wait a couple more runs before given an impact opinion but there could be a fujiwhara effect that comes into play as it comes into the Tasman.
IMO we are in the midst of a cut off low extravaganza due to what I have mentioned in a past post
https://www.weatherforum.nz/phpBB3/view ... 00#p177457 and MJO has just done a complete U turn on itself sending models wild
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Wed 21/11/2018 21:06
by snowchaser01
Cyclone Tracy wrote: ↑Wed 21/11/2018 20:59
Nice one Stormchaser, yes it’s an incredibly complex beast and has started to spin off South Australia driven by significant upper cold core cyclone. It's then going to spawn a second surface circulation off the NE coast of Tassie by tomorrow night, which then cuts off from the westerly flow while under going bombogenesis. UKMet showing near 970 hPa on Friday off the SE coast of OZ.
I’m going to wait a couple more runs before given an impact opinion but there could be a fujiwhara effect that comes into play as it comes into the Tasman.
IMO we are in the midst of a cut off low extravaganza due to what I have mentioned in a past post
https://www.weatherforum.nz/phpBB3/view ... 00#p177457 and MJO has just done a complete U turn on itself sending models wild
Certainly and interesting time, and a lot of unusual happenings going on. Even just the instability in the air down here today had an unusual feel to it, so early on in the day. I think this low in question has the potential to provide some very significant rain to the eastern SI?
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Wed 21/11/2018 21:27
by Bradley
snowchaser01 wrote: ↑Wed 21/11/2018 21:06
Cyclone Tracy wrote: ↑Wed 21/11/2018 20:59
Nice one Stormchaser, yes it’s an incredibly complex beast and has started to spin off South Australia driven by significant upper cold core cyclone. It's then going to spawn a second surface circulation off the NE coast of Tassie by tomorrow night, which then cuts off from the westerly flow while under going bombogenesis. UKMet showing near 970 hPa on Friday off the SE coast of OZ.
I’m going to wait a couple more runs before given an impact opinion but there could be a fujiwhara effect that comes into play as it comes into the Tasman.
IMO we are in the midst of a cut off low extravaganza due to what I have mentioned in a past post
https://www.weatherforum.nz/phpBB3/view ... 00#p177457 and MJO has just done a complete U turn on itself sending models wild
Certainly and interesting time, and a lot of unusual happenings going on. Even just the instability in the air down here today had an unusual feel to it, so early on in the day. I think this low in question has the potential to provide some very significant rain to the eastern SI?
Latest EC run going for 200mm for places like Sheffield for Sat-Thu and 100mm for Christchurch, already sodden ground = flooding for low lying areas of Christchurch
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Wed 21/11/2018 23:11
by Chris W
Keep the second half of next week in mind as well, it is a long way out but current modelling (GFS, Metvuw) has another low following on and looking to deliver a lot of rain to the eastern South Island.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 06:31
by snowchaser01
GFS had pulled back slightly yesterday, but this mornings run has increased again up to 100mm for the airport for the next 10 days. Not sure what model i trust more with these events... GFS or EC? EC currently saying near enough to double what GFS is.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 06:40
by Bradley
snowchaser01 wrote: ↑Thu 22/11/2018 06:31
GFS had pulled back slightly yesterday, but this mornings run has increased again up to 100mm for the airport for the next 10 days. Not sure what model i trust more with these events... GFS or EC? EC currently saying near enough to double what GFS is.
I’d usually say EC but the last few big rain events GFS has been more accurate 3-4 days out, EC seems to be struggling more with the current state of the atmosphere...
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 06:50
by snowchaser01
Bradley wrote: ↑Thu 22/11/2018 06:40
snowchaser01 wrote: ↑Thu 22/11/2018 06:31
GFS had pulled back slightly yesterday, but this mornings run has increased again up to 100mm for the airport for the next 10 days. Not sure what model i trust more with these events... GFS or EC? EC currently saying near enough to double what GFS is.
I’d usually say EC but the last few big rain events GFS has been more accurate 3-4 days out, EC seems to be struggling more with the current state of the atmosphere...
All these systems seem to be backing off slightly a few days out, well on GFS they do anyway. We shall see i guess.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 07:33
by NZstorm
Looking like elevated thunderstorms possible early Saturday over the upper North Island with warm front.
Then unstable over the weekend.
Total rainfall from UKmet model for next 6 days
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 08:41
by Cyclone Tracy
Upper low is now over SE OZ and is calling all of the shots. Initial surface low to be consumed by a bombing cyclonic Tasman gyre later today. Will look pretty impressive on tomorrow mornings sat pic.
IMO, you can't look past the weekend at the moment, as circulation, cut off position, steering and forward speed of the extratropical cyclone is only a vague mathematical guess. Models will currently serve up junk from 96 hours onward. Mid latitude cyclones are one part of weather, that all models have yet to grasp with high accuracy before they circulate.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 08:56
by spwill
This current model pattern is something you expect to see in May, not November when highs and westerlies usually dominate the Tasman and NZ.
We move from cool unstable to warm unstable by Saturday.
It has been on the dry side this November for northern NZ but that is about to change. MS Whangaparaoa only showing 17.6 mm so far for November.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 11:06
by melja
A good test for the highway around kaikoura by the looks, don't want any significant damage this close to Xmas as it's almost a bearable drive at this point.
Sent from my Redmi Note 4 using Tapatalk
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 12:29
by Richard
GFS have insane numbers for the next week, over 300mm for here, been a long time since there's been any major flooding, oh well, need a new supply of mortar sand in the river
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 12:30
by snowchaser01
Cyclone Tracy wrote: ↑Thu 22/11/2018 08:41
Upper low is now over SE OZ and is calling all of the shots. Initial surface low to be consumed by a bombing cyclonic Tasman gyre later today. Will look pretty impressive on tomorrow mornings sat pic.
IMO, you can't look past the weekend at the moment, as circulation, cut off position, steering and forward speed of the extratropical cyclone is only a vague mathematical guess. Models will currently serve up junk from 96 hours onward. Mid latitude cyclones are one part of weather, that all models have yet to grasp with high accuracy before they circulate.
I agree with you re the models currently. They seem to be all over the place. Latest Metvuw (gfs) has easterly rain in Canterbury on Saturday, Sunday and heavy on Monday and Tuesday... and possibly Wednesday. Concerning to say the least. 200mm atleast against the foothills on current data.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 13:21
by Tornado Tim
A very interesting pattern emerging in the models with this next upcoming system, NW to Northerly attached with a rather elongated trough of low pressure in the Tasman could infact be dragging in the cooler air after the tropical feed comes in before hand.
If that forecast eventuates, then the Upper half of the North Island should become Thunderstorm central for a few days early to mid next week.
Will have to see how the models develop the prognostic
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 15:35
by snowchaser01
For future reference MetService mentions a high confidence of heavy rain for Otago all the way up to far North Canterbury on Sunday and Monday.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 17:56
by snowchaser01
HOLY HECK!! This is the latest gfs data for CHCH airport over the next 10days. 172mm?! That would surely cause problems.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 18:09
by Bradley
snowchaser01 wrote: ↑Thu 22/11/2018 17:56
HOLY HECK!! This is the latest gfs data for CHCH airport over the next 10days. 172mm?! That would surely cause problems.
Not so much the first wave but the second wave starting next Friday if it eventuates would cause some problems for certain!
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 18:18
by snowchaser01
Bradley wrote: ↑Thu 22/11/2018 18:09
snowchaser01 wrote: ↑Thu 22/11/2018 17:56
HOLY HECK!! This is the latest gfs data for CHCH airport over the next 10days. 172mm?! That would surely cause problems.
Not so much the first wave but the second wave starting next Friday if it eventuates would cause some problems for certain!
Agreed, however it only takes 40-50mm to start causing problems in chch. IF you start nearing 100mm then the heathcote starts to struggle. I remember 2014(?) 3 massive rain events in a few months of 100mm plus in ChCh, it was not good at all.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Thu 22/11/2018 21:29
by Cyclone Tracy
Both EC and GFS on the 00Z are loading up 2 upper tropospheric cyclonic vortexes (UTCV) over the Tasman on Saturday morning. Starting to look like a Fujiwhara effect set up around NZ next week.
I’ve also spotted another coupling of the Stratosphere and Tropopause that supports another cut off UTCV right behind it. This one might have a butterfly effect on the tropics for mid to late December South Pacific Tropical cyclone.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Fri 23/11/2018 07:38
by NZstorm
Looking like some decent thunderstorm activity possible for the upper North Island this weekend. Two troughs coming through, one tomorrow morning but the most unstable trough looks to be Saturday night/Sunday morning. Some of the models like UKmet have over 100mm rainfall for parts of Auckland/Northland. Its a case of watch and see what eventuates.
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Fri 23/11/2018 10:15
by Bradley
Both EC and GFS have back right off for rainfall totals for mid Canterbury with Christchurch only going for 40mm for the whole event now, seems to be the story of the last few big events with the models dying away leading up to the event for mid Canterbury...
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Fri 23/11/2018 11:10
by Richard
Yes, looking more northern North Canterbury and kaikoura coast at this stage
Re: Deep Low to Impact NZ... AGAIN (24th to 28th Nov)
Posted: Fri 23/11/2018 11:34
by snowchaser01
In all honesty though, the models have been up and down like a yo-yo for the last week or so. Struggling to keep up with the atmospheric conditions currently. Less than 24hrs ago, they were picking more than 4x what they are currently saying for ChCh. Don't be surprised it it swings back on tonights run.