Deep Low: 7th Oct

[Vertigo]

Models show a deep low crossing the south island, with associated rainband extending through northland and BOP. Fast mover this one, shell be gone by the next day.

Valid: Sat 04 Oct to Tue 07 Oct
Issued: Thu 02 October 2008 at 0207 pm

SWO Threat Situation valid from Saturday 04-Oct-2008 to Tuesday 07-Oct-2008

Issued by MetService at 1:41pm Thursday 02nd October 2008

A cold front is forecast to cross the South Island on Saturday, bringing a period of heavy rain to the Southern Alps and West Coast, with a high confidence of rainfall accumulations reaching warning criteria. Strong northwesterlies are also likely in many eastern areas ahead of the front, and winds may reach severe gale for a time about exposed parts of Wairarapa, Wellington and Marlborough during Saturday and early Sunday.

The front is expected to become slow moving over the lower half of the North Island on Sunday, but should gradually weaken, with easing winds. There is a low to moderate risk of significant rainfall over the Tararua Ranges and Mt Taranaki from late Saturday into Sunday.

Another front is expected to cross the South Island late Monday or Tuesday, with an associated deep low passing just south of Foveaux Strait. This system is forecast to bring another period of heavy rain to the Southern Alps and West Coast, with warnable amounts of rain likely. It is also expected to bring a period of very strong northwesterlies to southern and central New Zealand, with a low to moderate risk of these winds reaching severe gale for a time as per the chart. The front should cross the North Island during Tuesday, bringing a period of heavy rain to western parts of the island. There is a moderate risk of rainfall amounts reaching warning criteria about the Tararua Ranges and Mt Taranaki during this time and possibly into the hilly country from inland Taranaki across to Mt Ruapehu.

Model run from Metservice...

[NZstorm]

There looks to be a big area of cold unstable air crossing the South Island Wednesday with this system.
Current modelling suggest a large area of negative LI's Wednesday afternoon. This type of situation would be more fruitful for storms in December but thunder/hail still likely I think for east coast South Island on Wed.

[NZstorm]

The major trough this week looks like it could be interesting, in an nutshell, heavy rain and gales over the west/central North Island Tuesday, squally thunderstorms/hail to the west and south of the South Island Wednesday, thunder/hail spreads into the to North Island Thursday and conditions get colder in the south of the South Island Thursday with snow to quite low levels (500m maybe a bit lower).

On Wednesdays weather, the strong westerly flow will likely keep shower activity offshore north of Dunedin. Thunder/hail south of Dunedin in a cold unstable air mass, particularly around coastal Southland.

[NZstorm]

Pic here of 500mb temps for Thursday.

[David]

Tuesday really is looking wild - look at the latest outlook!
Looks like a great day to go up to the Manukau Heads!

[Manukau heads obs]

Looks like a great day to go up to the Manukau Heads!

David, if you can get out this way at all, then we could have a weather meet tuesday afternoon up there, LOL

[David]

David, if you can get out this way at all, then we could have a weather meet tuesday afternoon up there, LOL

Haha that would be awesome, I'm still on holidays - but don't have a car!

[Storm Struck]

Abit cooler today after yesterdays 27C maximum, also some rain sometime in the early hours.
Its abit of a shame where the low is forecasting to track at the moment as to whether it drags up some nice pools with it or not, but i am sure something will happen here.
Maybe a chance on Wednesday afternoon/evening for thunderstorms with the cold SW change, the numbers are there for it just not quite the moisture even though convective development can enhance that.
Cheers
Jason.

[jamie]

Mr Miller said up to 200ml could fall in the Tararua Ranges and up to 150ml in the hilly country around Taranaki and Lake Taupo. from the NZ herald

[Vertigo]

looking a little less likely to produce what id really like, but itll still be fairly wet.

Valid to: 00:00 am 8 Oct 2008 NZDT
Issued at: 11:00 am 6 Oct 2008 NZDT

A band of heavy rain preceded by gale northwesterlies is expected to cross the North Island on Tuesday. But for much of the period, thunderstorms are not expected with this feature. There is some indication however that the front may become more unstable during the evening hours as it moves across Coromandel Peninsula and Bay of Plenty. So there is a low risk (possibly higher) that a few thunderstorms my trigger on the front as it moves across these areas, especially over the eastern Bay of Plenty/northern Gisborne ranges.

[mikestormchaser]

High risk MS are saying for thunderstorms in Canterbury tomorrow, whats your thoughts on this NZstorm??
NE against S would be ideal for a big thunderstorm tomorrow lets hope for that..I wouldn't worry to much bout moisture levels at the moment if the numbers are there.

[gllitz]

Hmmm...Meteograms are showing action possible for WED, not tomorrow...lifted index is about 0 or so (good for t'storms) CAPE is around 150 (which is LOW, but at least it is high-"ish" for Canty), but what I don't like is the w/nw winds and very low temps and even lower dew points...not good for convection, I thought...the M/S are saying the surface Easterly will clash with the westerly tomorrow and get things fired up...I just don't know and can't tell, as there seems to be a discrepency b/w models...pass...can't make a call on this...over to the storm experts on this one...

[NZstorm]

Southerly change looks to be through Christchurch by midday and the upper level support by way of an upper short wave doesn't come in until late afternoon/early evening. So I don't see thunderstorms in coastal Canterbury tomorrow but could well be a thunderstorm or two in the NW ranges late afternoon.

Yes Wednesday looks better, particularly for Dunedn to Invercargill.

Unstable air crosses the North Island Thursday according to GFS with a coolish dry surface SW. Looks to still be the chance of thunder/hail over Waikato/Auckland/Northland from this but will need to wait until nearer the day I guess to be sure.

[Storm Struck]

Well it does look reasonable for tomorrow.
After early morning rain which should clear for some day time heating is one factor.
The other is the most likly more NE flow pushing inland to meet the W-NW winds near the Foothills and combining with the cooler SW change later on.
It should be an interesting day i would think.
Wednesday doesnt have enough moisture and is too dry under a more Westerly flow.
Will the SW change at midday be an influence from the rain crossing to the south NZstorm? because if it is the SW may die off and allow a NE to kick in which is very simular to what happend last Wednesday.
Cheers
Jason.

[NZstorm]

the SW may die off and allow a NE to kick in which is very simular to what happend last Wednesday.
Cheers

If it was summer a late afternoon NE would be more likely. Looks like the flow will remain WSW through afternoon.

As for Wednesday, yes a dry westerly will likely prevail in Canterbury.

[Willoughby]

There is a heck of a lot of moisture in the northwest flow!

Pretty dank day here today with constant drizzle, turned heavy at times too.

[jamie]

Well auckland rain radar is down...be honest, who is actually suprised?

[Manukau heads obs]

cloud base lifted today, which is good, as yesterday the coastal hills were in the clouds...not good for strong wind chasing this sarvo

the wave depression traveling down the front is visible on the sat picture...thats whats going to ramp up the winds this afternoon...which have gone northerly now...the strongest winds will occur at the Manukau heads when the NNW wind develops down the west coast here, an hour or 2 before the cold front ....as a sudden pressure release....should be good if all goes to plan

[Manukau heads obs]

wind picking up alot here now, and getting real gusty too
looks like its going to be a hum dinger this afternoon alright!

[Michael]

ZB said NW to 35 knots changing SW 30.Its like a mill pond at my place now but then we can double it when it goes SW.Swings and roundabouts I guess.

[Shepherds Valley WX]

Morning lads,

Bit of a blow here in Upper Hutt this morning, my station set a new wind gust record (only NE 48.3 kmh) but we are in a very sheltered valley. At the top of the Blue Mountains, I would suggest that its really strong as the old pine trees I can see up there are howling in the gale! I also see that Wellington Airport has suspended some flights .... so it must be a reasonable "breeze"down there as well.... I wonder how things are up Kapiti/Levin way with all the rain forecast for the Tararuas? Not much spillover this side with 22mm since midnight.

Be interested to hear how other Wellington stations are going?

Great fun watching Weather Display this morning.... some good gusts coming through with horizontal rain, most likely missing the rain guages!

UPDATE 1111am : Just recorded wind gusts on both of my anemometers of over 100km/h! Wind really pumping in to our valley now as it has moved around slightly to a true NW and is hitting us full on... at first I thought anemometer fault, but I have now recorded the gusts on two seperate 1-wire sensors....am starting to get nervous about pine trees above us!

[Storm Struck]

1.5mm of rain here this morning has moved off with the sun making an effort to come out, already SW although it has eased off quite abit now which makes me wonder if the NE will sneak in this afternoon.
MS still seems to think a high risk, yes if the coastal breeze gets going but otherwise i am not so sure.
14.8C and slowly rising, looks like some of the rain got heavy off BP in the early hours, and also started raining out that way first which was possibly the weaker front connecting.
Should be an interesting day for much of NZ.
Cheers
Jason.

[Shepherds Valley WX]

Heavy rain here now and a gust just recorded in excess of 130 k/mh, my station has a clear line of site from the West to the the NE horizon and the wind is just hammering us....our elevation on the north facing hills above Silverstream Upper Hutt is around 130m according to the GPS....

This report on the NZ Herald site just updated shows the Rimutaka Hill Rd has been closed:

Rimutaka Hill is also closed until at least 12pm "due to excessive winds", Inspector Marty Parker said.

Radio Network weather analyst Philip Duncan said there was a report of a wind gusts of 160km/h hitting Mt Kaukau in the capital.

Earlier, he reported gusts of 102km/h downtown in Wellington. Further north, the Manukau Heads are experiencing gusts of 83km/h.

MetService forecaster Ian Miller said the Rimutaka hills have already experienced winds of 140km/h and "it probably hasn't peaked yet'.

He said winds could reach 160km/h and cause problems for campervans, motorcycles and high sided trucks.

[Shepherds Valley WX]

Update 1158am - have lost both anemometers on station. 1-wire sensor still intact but damaged and has taken down the rest of the 1-wire sensor network so will have to switch over to the Lacrosse wind sensor which is still hanging in there!

[David]

Wow that is huge wind gusts!! I just looked at your site and yes looks like the wind sensors are gone
The island bay site is also recording gusts to 132km/h