Deep Subtropical low 4th/5th January

[Cyclone Tracy]

All the big models are on board now. They believe a mothership upper low is going join forces with a surface low to spawn a 200+ mm water bomb over the North Island at the end of this week if it comes off. Latest EC is modelling an aggressive 987 hPa cyclonic Tasman gyre with a 40 to 50mm Precip water. Bay of Plenty looks wet but this will wobble around on each model run. Decent flow on effects to be felt across most of NZ. Time will tell I suppose...

[tgsnoopy]

All the big models are on board now. They believe a mothership upper low is going join forces with a surface low to spawn a 200+ mm water bomb over the North Island at the end of this week if it comes off. Latest EC is modelling an aggressive 987 hPa cyclonic Tasman gyre with a 40 to 50mm Precip water. Bay of Plenty looks wet but this will wobble around on each model run. Decent flow on effects to be felt across most of NZ. Time will tell I suppose...

I hope it's wrong, don't need any 20mm/hr+ events here until post some changes I intend to make (which can't happen until trade suppliers resume 2018 normal business hours). Enough of the flooding, can do without it.

[midgrove]

All the big models are on board now. They believe a mothership upper low is going join forces with a surface low to spawn a 200+ mm water bomb over the North Island at the end of this week if it comes off. Latest EC is modelling an aggressive 987 hPa cyclonic Tasman gyre with a 40 to 50mm Precip water. Bay of Plenty looks wet but this will wobble around on each model run. Decent flow on effects to be felt across most of NZ. Time will tell I suppose...

Where do these maps come from?

[Cyclone Tracy]

GFS and EC just keep upgrading.... Both having a cyclonic cut off surface low attacking the north island in the 970's hPas now. These simmering surface sea temperatures are going to create a warm advection machine. The time bomb has been ticking for a while now. I'd say the MetService severe weather dept would have sweaty palms after the 12z model runs.

Anyone camping on the north island, I'd start packing up the tent within the next 48 hours

@midgrove, maps are from an ECMWF related subscription I have. Not freely available.

[NZstorm]

Certainly an interesting low on gfs with a warm core resembling a tropical storm.

[Dean.]

Tonights run will be interesting...I may cancel local camping plans and head south this weekend.

[David]

Metservice forecast for Auckland looking grim mid-late week - says heavy rain and northeast gales Thursday night.

[Tornado Tim]

There is good model consensus on this warm cored low, which in itself being so far south in latitude being warm cored is unusual.
What concerns me most, is this is only the beginning of the warmup, the sea lags behind by around 3-4 months to reach peak, and already parts of the northern Tasman sea are close to beyond breaching 25*C according to satellite obs.
The extent of the warm water finger extends to a significant portion to the south which is very much helped by the east Australian current.

I would very much expect that the Tasman Sea esp on the western end toward Australia is going to become a potent brewing ground for these lows to develop.

[spwill]

I see EC has the low in a couple of days time moving across NZ more quickly now and away to the SE, GFS still has lingering low system.

[NZstorm]

I see EC has the low in a couple of days time moving across NZ more quickly now and away to the SE, GFS still has lingering low system.

I think the EC is likely correct with the subtropical low making a prompt exit. And EC brings in a big ridge for next week, so settled weather returns for the second week of January.

[David]

Hopefully the low doesn't exit too quickly, really need a good soaking. I see GFS rain estimates for Auckland are now around 50mm, down from 100mm. Hopefully doesn't drop too much further

[NZstorm]

A low will develop east of Queensland today and drift southeast toward NZ and deepen. The ECMWF has its centre near New Plymouth 6am Friday 977hpa.

The exact movement of the low will determine wind patterns but severe gales and big wing gusts look likely in exposed parts of the North Island.

Not a good weather system to be camping in as tree branches can come down.

[Richard]

Ive edited the other thread so as to separate it from this thread. I suppose this incoming low has no connection to the current period of convection.

[midgrove]

I have already seen one media report on the upcoming "weather bomb front" - whatever that is!. Strangely New Zealand is mentioned as a country where this term is misused the most, a sad reflection on our media.

[NZstorm]

Ive edited the other thread so as to separate it from this thread. I suppose this incoming low has no connection to the current period of convection.

Yes, its an entirely separate event and justifies its own discussion thread. We rarely get lows of this magnitude in summer.

[David]

Surprised there are no severe weather watches or marine warnings issued by Metservice yet

[treetopkk]

weather bombs were quite regular 10-20 yrs ago.[ie rapidly deepening depressions moving SE crossing middle NZ] been nothing since, ex cyclones have crossed NE of the country. Changing weather patterns ? is there much jet stream influence on this one ?

[NZstorm]

is there much jet stream influence on this one ?

Subtropical jet is behind the deepening. 120kts at 200mb.

[Cyclone Tracy]

Some good convective development in the last hour off the Queensland coast.

Access R high res 18z has a stronger significant hit across most of the NI. Now modelled at 970 hPa. GFS 18z is getting deeper as well. Full blown RI extra tropical cyclone if they are correct. MetService alarm bells not too far away now I would think.

[Cyclone Tracy]

2 surface circulations over 34 knots have now formed off Queensland with lightning on the north eastern flank of the circulation at 24S E158. Marine vessel movements on the east side of the upper North Island has increased quite a bit in the last 6 hours.

[Cyclone Tracy]

Equatorial like levels feeding into the atmospheric river. Currently 50 to 70mm.
http://tropic.ssec.wisc.edu/real-time/m ... anim=html5

[Cyclone Tracy]

00Z runs for the record. The main models have now come into alignment with Access R on strength and close to placement. Access R 969, GFS, 971 and EC 969hPa....

[NZstorm]

The frontal boundary moving down the from the north tonight has some low topped convection with it. That will be a favoured zone for localised severe gusts.

[cbm]

If ECMWF is right, this wind is going to funnel from the firth of Thames and hit parts of Waikato and King Country that rarely see strong winds.

wind.JPG

[Cyclone Tracy]

Cape Reinga now down to 1003 hPa. Rapid Cyclogenesis about to commence on a synoptic scale. Marine wind obs now 45 knots on the eastern flank. Warm fronts currently moving down into the upper NI with temps reaching into the -50c's on the cloud tops. It's show time