[Grant]

Periods of heavy rain are due into Central parts during the start of December, looks possible for some convective activity during that time also.

Quote

On Monday, a trough and associated rainband are forecast to spread onto central New Zealand from over the Tasman Sea. The trough and rainband are expected to remain slow moving over the area until Wednesday. During this period, heavy rain is likely at times about the hills and ranges of the North Island from Waikato down to the Tararua range, and also about the ranges of Buller and northwest Nelson in the South Island. Confidence is high that rainfall accumulations will reach warning amounts about Mount Taranaki, The Tararua range and also the southern part of the Ruahine ranges; while for surrounding areas from Tongariro National Park down to Buller, confidence is moderate. A heavy rain watch is already in force for these areas. For the hills and ranges of Waikato and Taupo during the same period, the probability of heavy rain reaching warning criteria is low.There is also a low probability on Wednesday, that rainfall accumulations will reach warning amounts about the ranges of Gisborne and eastern Bay of Plenty.The trough should move north over the North Island later on Wednesday, while a ridge of high pressure is forecast to spread onto the South Island. On Thursday and Friday the ridge should persist over the South Island, while a northeasterly flow covers the North Island.
http://metservice.co...er-outlook.html

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[Grant]

It could be quite an interesting few hours, if anything materialises. Does anyone have up to date cape charts etc?

Quote

Valid to: 12:00am 2 Dec 2009 NZDT

Issued at: 12:32 pm 30 Nov 2009 NZDT

Over northern New Zealand conditions are expected to become very humid with rain at times. There is moderate risk of isolated thunderstorms from Northland to Taupo and western Bay of Plenty in the afternoon and evening with gusty winds.The risk is lower as far south as Wanganui and northern Manawatu and as far east as Gisborne and Hawkes Bay.

A low is expected to lie west of Buller by evening, bringing humid air onto northern and central parts of the South Island. One or two thunderstorms could trigger on a slow-moving front over Buller but the risk is low at this stage.

There may be sufficient breaks in the cloud from the McKenzie basin to inland Otago in the afternoon or early evening for isolated thunderstorms to form as an upper trough approaches. Likely slow storm motions means the risk of localised heavy rain. There is only a very low risk of any thunderstorms further north as far as the inland Kaikoura Range.

http://metservice.co...understorm.html

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•  756c-12543ac8f00-1254a1c8200-1254249e747.gif (11K)
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[Tornado Tim]

WOW, this is 2 days from Monday!
Cape of 750+ j/kg!!
My forecast is outlining the 3rd of December is being good.
 aus6.48hr.png (53.17K)
Number of downloads: 5

This post has been edited by Tornado Tim: 30 November 2009 - 09:03 PM

[David]

Grant, on 30 November 2009 - 08:38 PM, said:

It could be quite an interesting few hours, if anything materialises. Does anyone have up to date cape charts etc?

Although we will have nice high dewpoints in the north tomorrow, ideally we need some surface heating, i.e. sunshine!

Here's a CAPE forecast chart for the north tomorrow at 4pm NZ time.
 1stDecember4pmCape.gif (18.36K)
Number of downloads: 10

[David]

Here's the GFS CAPE forecast for the next few days for Auckland, shows CAPE to 900 at 4pm tomorrow, thats decent :icon_mrgreen: But its contradicting my previous GFS chart!! Hmmmmm....
 28391095_metgram.gif (22.94K)
Number of downloads: 2

This post has been edited by David: 30 November 2009 - 09:15 PM

[Grant]

Not ideal and looking at the GFS for tomorrow the chances of sunshine for you guys is pretty slim :icon_mrgreen:

[Tornado Tim]

David, on 30 November 2009 - 09:03 PM, said:

Although we will have nice high dewpoints in the north tomorrow, ideally we need some surface heating, i.e. sunshine!

Here's a CAPE forecast chart for the north tomorrow at 4pm NZ time.
1stDecember4pmCape.gif

Yup DTSH is the determining factor, its not looking unstable enough for my liking so I am playing tomorrow down for the moment.
Skew-T chart for tomorrow at 4PM NZDT.
 Screen shot 2009-11-30 at 10.07.45 PM.png (26.54K)
Number of downloads: 4

[David]

Metservice have upgraded the risk to high for some areas.

Quote

Conditions over much of the North Island and upper South Island should become more unstable during the afternoon, with humid air and rain or showers in most places.

The highest risk of thunderstorms is forecast on a convergence line expected to form in the afternoon from southern Northland, through Auckland to inland parts of Waikato and Bay of Plenty. Additionally, there is a moderate risk of isolated thunderstorms in the afternoon or evening from Northland down to Waikato, Taupo and western Bay of Plenty. Any storms that eventuate in these areas may bring localised heavy rain with rates up to 25mm/hr.

For the South Island, there is a moderate risk of isolated storms developing about the Mackenzie Basin and inland parts of Otago in the afternoon or evening bringing locally heavy rain. Later, during the evening and night hours, a low with a supporting upper trough should approach Buller and northwest Nelson with a moderate risk of thunderstorms there.

Adjacent areas to those described above, including much of the North Island from Kapiti northwards, have a low risk of thunderstorms as indicated on the chart.Elsewhere, no thunderstorms expected.

http://www.metservic...understorm.html

 stormoutlook1Dec.gif (12.75K)
Number of downloads: 11

[Tornado Tim]

David, on 30 November 2009 - 09:18 PM, said:

Metservice have upgraded the risk to high for some areas.


http://www.metservic...understorm.html

stormoutlook1Dec.gif

Hmmm,
I am still apprehensive about that forecast.
I think the upper air temps are too warm.
I know Matangi is in the "High Risk" area, but im not so sure it will pan out.
The determining factor is if we get sunshine on not.

[Grant]

I think its very much reliant on the surface heating and going on yesterdays charts, there will be a need for the cloud cover to thin out a bit.

[ATO2]

Grant, on 01 December 2009 - 08:28 AM, said:

I think its very much reliant on the surface heating and going on yesterdays charts, there will be a need for the cloud cover to thin out a bit.

Well, I was just looking over this thread. We did get 50mm+ out of it and no thunder, so those met service predictions were OK except it seems to have been a day earlier.

This post has been edited by ATO2: 01 December 2009 - 08:36 AM

[Grant]

Interesting possibilities for North Island over the next 24 hours with regards to the thunderstorm outlook.

Quote

An active convergence line lies from just north of Great Barrier Island to near Leigh and is expected to move slowly southwards today to lie over the northern tip of Coromandel Peninsula and Auckland city this evening.
Thunderstorms are expected to develop on this line by late morning. They should
intensify during the afternoon as temperatures cool aloft in reponse to an
approaching upper low in the Tasman Sea. Thunderstorms are expected over
southern parts of Northland in a separate seabreeze convergence line though
these should clear this evening. Thunderstorms should spread to most parts of
Auckland and northern areas of Coromandel Peninsula.
Some of these thunderstorms in Auckland city, northern parts of Auckland, the
islands of the Hauraki Gulf and the northern tip of Coromandel Peninsula may be
severe with sustained downpours of 25 to 35mm per hour possible.

http://metservice.co...erstorm-outlook

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•  sat1.png (9.99K)
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[Grant]

A severe thunderstorm watch has now been issued for the 4th December 2009, by Metservice. Details at http://www.nzweather...-december-2009/

[Derek]

If they are tracking south east, they will probably just miss our place... we may not have power when we get home though...

[David]

Starting to look like it won't happen. Still no heavy rain here...

[Grant]

Could be interesting if any of these predictions come to fruition for the 5th December. Certainly a chance of late convection with current conditions.

Quote

Valid to: 12:00am Sunday 6 December 2009
Issued at: 8:32am Saturday 5 December 2009


Thunderstorms along the Coromandel Peninsula earlier this morning have now gone,and no more are expected. The heavy rain warning is still in force, but the rain is now tailing off.

There is a moderate risk that thunderstorms will pop up this afternoon and evening about the ranges of Marlborough south of the Wairau River, also about the Canterbury foothills and parts of central Otago. These thunderstorms are likely to be slow moving, and could produce localised rainfall rates of 15 to 25mm per hour. There could also be some small hail.

A lower risk of thunderstorms extends across to the northern Marlborough ranges,also to the southern Nelson ranges and into inland Southland.

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•  thunder.gif (10.06K)
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[Tornado Tim]

Depending on the conditions we may get a taste of this:
 Linghtning Image.jpg (249.15K)
Number of downloads: 3
The tasman is very active this evening :)

[Grant]

Yes the NZ Weather Storm Tracker is picking it up nicely tonight

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[Grant]

A couple of things to note with regards to the situation over the next 24 hours into the 9th December 2009. MetService has a thunderstorm warning issued - see http://www.nzweather...-december-2009/ but also there is a planned power outage for my area between 08:00 and 18:00 on the 9th December, which will mean the storm tracker at http://www.nzweather.net/storm.html will be offline. :icon_wink:

Valid to: 12:00pm Wednesday 9 December 2009
Issued at: 9:40am Tuesday 8 December 2009

A front is expected to lie over the southern South Island on Wednesday morning,while a moist unstable northwesterly flow affects the west coast of the South Island.

Heavy rain and embedded thunderstorms can be expected about Westland and the Southern Alps during the morning, with a lower risk of storms about Fiordland earlier in the morning, and Buller late morning. Some of these thunderstorms will probably be severe with rainfall rates exceding 25mm/hr. This could lead to some high rainfall accumulations, and a Heavy Rain Warning is force for Westland, Fiordland and the headwaters of Canterbury and Otago.

Valid to: 12:00am Thursday 10 December 2009
Issued at: 9:37am Tuesday 8 December 2009

Further rain and thunderstorms can be expected about Westland and Buller during Wednesday afternoon and evening, with the thunderstorm activity moving slowly northwards during the day. Further severe storms are likely in Westland during the afternoon with rainfall rates exceding 25mm/hr, but the rainfall rates should ease a little over Westland in the evening.

In the east of the South Island, a southerly wind change will move northwards through Otago late morning and afternoon, and through South Canterbury in the late afternoon and evening. It is possible a few thunderstorms may develop on this wind change, but at this stage this risk of storms is considered low. If any storms do develop, they are more likely inland.

http://metservice.co...erstorm-outlook

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•  t1.gif (9.46K)
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[Tornado Tim]

Grant, on 08 December 2009 - 06:05 PM, said:

but also there is a planned power outage for my area between 08:00 and 18:00 on the 9th December, which will mean the storm tracker at http://www.nzweather.net/storm.html will be offline. :icon_cool:

Thats a real shame you have the PCI version..... The Boltek LD250 can run without mains power.
That reminds me I will have to get a UPS for my webserver before it goes online.