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.
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
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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?
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
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.
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.
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...
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.
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.
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.
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.
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
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.
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
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!
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.
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.
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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.
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...
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.
