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Low for North Island Tues/Wednesday

Posted: Sun 21/12/2008 10:16
by NZstorm
A small low is forecast to develop near New Caledonia today and will move quickly south and pass near East Cape early Wednesday. Looking like some rain for many northern and eastern regions of the North Island Tuesday/early Wednesday. The low doesn't look like much to get excited about though with no instability forecast apart from maybe in Gisborne. And the humid warm advection will pass east of the country. Forecast rainfall for Auckland is 20mm. According to GFS winds look like reaching gale force about exposed eastern areas from Northland to East Cape. The UKmet has the low passing just a bit further east with lass rain/wind for the NI. We will see what happens.

Re: Low for North Island Tues/Wednesday

Posted: Sun 21/12/2008 11:06
by Tornado Tim
NZStorm wrote:The low doesn't look like much to get excited about though with no instability forecast apart from maybe in Gisborne.
Funny that because i just got this and it says that Auckland has got some instability coming around on Tuesday at 1800 hours, However it does not look like much.

Re: Low for North Island Tues/Wednesday

Posted: Sun 21/12/2008 14:25
by Michael
The map for Tuesday 1pm has the best prospect then Xmas day.....back to you know what.This was uploaded from the Metsercice rain tracker.

Re: Low for North Island Tues/Wednesday

Posted: Sun 21/12/2008 19:30
by NZstorm
Yes the 00Z GFS is now a bit more agressive with the moisture with 17-18C dps getting onto the North Island with possible destablisation Wednesday. Certainly seems to be a little bit of thunderstorm risk for us with this system now. But the UKmet keeps the very moist air just out to our east. For the instability it all comes down to those dewpoints, whether they come our way or not. No doubt we will see more changes in the details of this system in the coming model runs.

Re: Low for North Island Tues/Wednesday

Posted: Sun 21/12/2008 22:26
by Vertigo
looking very nice. will probably lose its convective activity before it gets here tho.

Re: Low for North Island Tues/Wednesday

Posted: Mon 22/12/2008 07:33
by NZstorm
will probably lose its convective activity before it gets here tho.
Possibly, instability in this type of system can be fickle. GFS suggests the low will bring a bit of a thunderstorm risk into the north late Tuesday and this will spread south Wednesday. Afternoon heating Wednesday afternoon will favour further cb development over the west of the NI.

Chart here of modelled lifted index values for 12Z Tuesday (1am Wednesday). I have included 500mb winds which suggest good wind shear with this system.

Re: Low for North Island Tues/Wednesday

Posted: Mon 22/12/2008 18:00
by Manukau heads obs
just back from being over in the coromandel over the weekend
bit of a heat shower over waiuku this aftenoon against the sea breeze :)
will be good to get the rain from this low from the north!

Re: Low for North Island Tues/Wednesday

Posted: Mon 22/12/2008 18:05
by Tornado Tim
Looking at the GFS tomorrow looks quite promising for Auckland to get thunderstorms.
DP:15
Cape is good and lifted index is good also with -2 to -3 values.
Hopefully it pans out for you guys up north from me.

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 07:11
by NZstorm
The system will pass off just to the east of us now by the looks. I hope we still get some rain here in Auckland but with a S/SE we could miss out.

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 07:47
by spwill
Looks like another sub tropical Low will be moving down later in the month. Bad news for holiday makers but atleast it's another rain opprotunity for farmers.

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 08:35
by Nev
Yes, ideally we'd be very happy if our tanks were topped up before Xmas - here's hoping!

MetService have a Gale warning in force for the Hauraki Gulf later this morn. Was relatively calm and sunny here earlier, but, about 100 km NE of Akld, winds at 7am were already at 67 km/h.

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 08:59
by Manukau heads obs
still looking like some usefull rain me thinks for the auckland area are a coming :)

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 09:47
by Tornado Tim
Northern Waikato has got some Altocumulus Castellanus.
If this South Easterly continues, Waikato might get a thunderstorm later on.
The GFS does not think so..... it seems to think all the instability has shifted past the coromandel area.
We will see.

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 09:56
by Vertigo
an interesting spin-up west of cape reinga this morning, associated with the ex-tropical low moving east of us. looks like a small cyclone in its startup stages, but much too shallow.

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 17:51
by Nev
Was 21°C here just after midday - down to about 15°C now. Light rain from about 4pm. The highest of the E'erly winds predicted for the Hauraki Gulf earlier today seem to be staying well offshore...

Mean Winds at 4pm:
Waitemata Harbour - 44 km/h
Tiritiri Lighthouse - 61 k/h
Colville Channel - 82 km/h
Mokohinau Islands - 85 km/h

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 19:02
by David
Rain arrived here around 5pm but is very intermittent - up to 5mm so far from quick heavier bursts mainly. Interestingly the SE has completely died off and there is now a southerly with only 14C? :?

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 19:47
by Vertigo
large dollop of red on the latest auckland rain radar! brian, did you catch that? looks close to you.
also noticing some electrical activity around this system.

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 19:54
by spwill
There was a brief Thunderstorm out in the Hauraki Gulf between Waiheke and Coromandel .
Up to 22C today with a sunny morning. Rain now, heavy at times, 14C.

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 20:41
by Manukau heads obs
we have had some good rain here so far....11mm now :)
looks like there was some lee trough amplificaiton going on there Vertigo

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 23:14
by Nev
Interesting - must've missed those strikes. Over 19mm here so far, Kerikeri nearly up to 60mm and both Whangarei and the Coromandel's Pinnacles over 30mm.

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 23:36
by NZstorm
27mm at Grey Lynn so far this evening. This system certainly did amplify. You can see that unstable air/cbs out to the east of Northland on sat pic.

Re: Low for North Island Tues/Wednesday

Posted: Tue 23/12/2008 23:45
by CHCH Weather Chaser
Looks very neat the Auckland radar, has done for a few hours now. Looks like it is fairly slow moving as well! Some good rain totals to be made by the looks of it. Possibly another one coming next Tuesday as some models are picking. Very strong winds here at the moment in Christchurch, fine with a NE gusting up to 65km/h.

Re: Low for North Island Tues/Wednesday

Posted: Wed 24/12/2008 05:47
by Manukau heads obs
50mm here now, to 5:45 am, and still raining nicely
great xmas present for the farmers in the district!

Re: Low for North Island Tues/Wednesday

Posted: Wed 24/12/2008 06:46
by Vertigo
just a question.. the latest 1am skew-t diagram for whenuapai shows pretty much constant 100% humidity all the way up to 500mb, and even further up its not much lower than 80%.. is this contributing to the heavy rainfall we are seeing from this system? never quite seen a diagram like this. its like the air is wringing water from itself.

Re: Low for North Island Tues/Wednesday

Posted: Wed 24/12/2008 07:23
by NZstorm
Yes, thats an impressive sounding. The precipitable water is 36mm which is a very high number for a sounding with surface dewpoint of just 12C! All that moisture in the middle of the sounding is where the rain obviously is coming from.

The GFS yesterday was forecasting 65mm for Auckland and Massey recorded 62mm! Grey Lynn got 42mm.