Deep low (XTC) June 11-13

[Cyclone Tracy]

A tropical disturbance has transitioned to a subtropical depression with a low level circulation centre currently positioned 700 km north of NZ. UKmet model was first to pick up the weakness in the ridge with all models now projecting an impact somewhere on the NI with flow on affects for parts of the SI.

Depending on development in the next 24 hours, it seems likely that the system will become an extratropical cyclone as it approaches the NI with wind gusts over 60 knots accompanied by significant rainfall totals on the SW and SE quadrants of the XTC. Currently the subtropical jet has been fractured by the upper cold pulse but will assist rapid development within 24 hours. MS have only just published the severe scale of the system, so several watches and warnings are now in place for the NI. Impacts on the SI will be better known within 24 hours

Here are the latest models projections from the 12z and 18z runs on the 10.30am sat pic on where the low may head towards the NI.

[NZ Thunderstorm Soc]

Not poor old Tologa Bay again

[Cyclone Tracy]

Yes, Tologa Bay maybe quite wet again....

Atmospheric river starting to organise across multiple layers. http://tropic.ssec.wisc.edu/real-time/m ... anim=html5

A little bit of wiggling on the models as you would expect. Parts of Canterbury also firming to be very wet as it tracks south. Significant winds before it crosses the NI coastline on the southern side. Media nice and quiet

[Ash]

Watching with interest.

[NZstorm]

Both UKmet and EU have the low moving into western BOP tomorrow morn.

UKmet has the 850mb jet at 70knots over western Bay of Plenty 12Z tonight, could translate into severe gales on the surface.

[Cyclone Tracy]

Plenty of moisture now in the mid levels. BOP around Tauranga is looking to be the crossing point as mentioned by NZstorm.

Rainfall depends on low movement. Around here UK and MS are going 60 to 80mm but it's game of pin the tail on the donkey really. Love how these systems still make the models struggle.....GFS moved the low 200 km east from the 06z to the 12z run

Here are the 12z latest runs with IR sat pic at 6.30am.

[Ash]

Looks wet.

[Cyclone Tracy]

Tauranga airport currently on 1017 hPa, centre of the low around 995 hPa and falling. 22 hPa pressure gradient within 400 km. This is going to squeeze hard into the ridge. Anyone on the eastern side of BOP, get the candles ready for this evening.

[spwill]

With the low center passing east of here not expecting much here in the east /southeast flow.

[Razor]

MS projecting moderately decent falls 30-40mm (by Christchurch standards) for us. That could be interesting on what is a pretty waterlogged region- we are already close to our annual average rainfall and not even mid year yet.

Watching with interest, especially the 3am high tide on Wednesday

[Richard]

A fall of 40mm+ will put this area also into 'waterlogged' territory

[TonyT]

A fall of 40mm+ will put this area also into 'waterlogged' territory

You may well get more than 40mm Richard.

[Richard]

Yes, its the type of weather system that may dump double the amounts along the hill ranges than on the plains.

[Cyclone Tracy]

She’s an asymmetrical ugly looking XTC now. Centre around 991 hPa looks to be slightly south west of where GFS, ICON and Access R 18z runs put her at this time. Seems like she might be S wobbling like an unbalanced washing machine which will mean she doesn’t have a straight line to the NI. A familiar comma head is now appearing on the IR sat pic with the associated mid level cloud. The pressure squeeze may intensify outer rain bands soon.

[Cyclone Tracy]

Latest Access R run taking the low through Tauranga , then the middle of the NI into the Cook strait with developing convergence zone down into the eastern side of the Upper SI. That may cause a few issues if it verifies.

[Razor]

Kaikoura might want to ready itself...

[spwill]

Max 11-12 C here today, mod rain here now.

[NZ Thunderstorm Soc]

Kaikoura might want to ready itself...

Yes. We don't want to loose the rail and road link again

[jamie]

MetService heavy rain watch includes me. Really hoping we don’t get more than 25mm but MS saying over 100mm is possible.


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[David]

Max 11-12 C here today, mod rain here now.

Yeah felt like a true winter's day. Possibly some heavier rain moving in from the east in the next few hours.

[melja]

8mm here today so already wet so don't need more. Was very wet with a fear amount of rain around the kaikoura hills area when I was up there today, not much in kaikoura town tho.

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[David]

Raining quite persistently here this evening, up to 13mm so far.

[Cyclone Tracy]

17mm here so far, southerly has picked up in the last 15 min.

Rapidly increasing water vapour levels being detected at mid to high level in the troposphere over the Bay of Plenty, the XTC is starting to mature and move in a SW direction into the BOP. Keeping a close eye on the radar on the western side of the XTC for developing rain bands heading towards the Coromandel and Auckland regions based off those upper levels of moisture.

edit: MS have upgraded watch to warning for Area: Coromandel Peninsula
Valid: 18 hours from 9:00pm Monday to 3:00pm Tuesday
Forecast: Expect 90 to 110mm to accumulate. Peak intensities 15 to 25mm per hour.
Changes: Watch upgraded to a Warning.
Issued by MetService at 9:15pm Monday 11-Jun-2018

[David]

A wet night here. Now up to 36mm since 2pm yesterday.

[Cyclone Tracy]

25mm here, XTC has slowed more than models thought within the BOP and showing good convective development near its core, strengthening the outer rain bands which have pushed into Auckland. Centre is around 984 hPa with the nearest ob on White Island currently on 992 hPa. Circulation looking good on radar now.