Unstable low over North Island Thurs 4th to Sat 6th

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NZstorm
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Unstable low over North Island Thurs 4th to Sat 6th

Unread post by NZstorm »

An upper trough with associated surface low with affect northern NZ next 3 days. Upper air is cool 500mb -21C with surface dps 13-14C, so unstable air.

Looking like thunder over Northland this afternoon with a front. Thunder possibilities over the North Island Friday/Saturday.

I am hoping for some surface heating Friday/Saturday to push up the instability numbers in the Auckland area.

500mb chart for Friday.
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by Nev »

I see MS have upgraded this arvo/evening's high-risk from about north of Orewa to Severe
MetService - Thunderstorm Outlook

Valid to: Midnight Thursday 4 Sep 2014
Issued at: 8:32am Thursday 4 Sep 2014

An active front northwest of the North Island containing thunderstorms is forecast to move over Northland this afternoon and evening to reach northern parts of Auckland and Coromandel Peninsula late tonight. Thunderstorms with this front have the potential to bring heavy rain with rates generally 10-25mm/hr.However, for eastern Northland and the far north of Auckland, there is a risk of SEVERE THUNDERSTORMS this afternoon and early evening producing localised downpours exceeding 25mm/hr. Additionally, there is a chance of one or two small tornadoes, especially about and near eastern coasts. A low risk of thunderstorms extends farther south to include the remainder of Auckland and Coromandel tonight.

Behind the front, an active trough is forecast to move over Northland tonight accompanied by heavy showers and a few thunderstorms. These storms may bring further bursts of heavy rain.

No thunderstorms expected over the remainder of the country, but a few showers on the central North Island ranges this afternoon could be heavy.
MetService Aug 4 T-Storm Outlook - Is. Aug 4.png
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by spwill »

Hopefully some surface heating Friday/Sat afternoons and not a cool cloudy rainy mess.
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by Nev »

And MS's Outlook for tomorrow morn…
MetService - Thunderstorm Outlook

Valid to: Noon Friday 5 Sep 2014
Issued at: 10:35am Thursday 4 Sep 2014

An active front near the Auckland region at midnight Thursday is forecast to move southwards over Coromandel Peninsula and Bay of Plenty during the morning to lie near Taupo by midday. Behind this front, a number of convective troughs are expected to rotate around a low over the Tasman Sea and onto the upper North Island.

There is a continued high risk of thunderstorms accompanying the front, affecting Coromandel Peninsula and Bay of Plenty before dawn. In these areas,localised heavy rain is likely with rates of 10-25mm/hr (or possibly more).Additionally, there is a chance of one or two small tornadoes, especially about and near the coast.

Behind the front over the upper North Island, there is a broad moderate risk of isolated thunderstorms as bands of heavy showers move onto the island from the northwest. These isolated storms may bring brief heavy rain. A lower risk of thunderstorms extends south to include Waitomo and Gisborne.

Elsewhere, no thunderstorms expected Friday morning.
MetService Aug 5 morn T-Storm Outlook - Is. Aug 4.png
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by CbFan »

Just had a stonker of a cell womble past Matauri Bay (at about 1500Hrs)
Dropped 20mm in as many minutes (and some scattered chunky hail) before heading off SW.
Couple of good sharp rumbles emerged from within, but no lightshow.
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by Manukau heads obs »

certainly lots of mama cloud here ahead of the front :)
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by NZstorm »

Thanks for the report cbfan.

Auckland managed a few spots of rain from the front. Clearing now.
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by David »

That front sure weakened dramatically!
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by treetop »

looking forward to intensifying shower activity over western BOP tonight. Usually get NE thunder after 10pm and before 6 am. Fingers crossed ,not a lot of wind with this one which will enhance any thermal activity as the moisture comes ashore and rises.
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by Manukau heads obs »

I see stuff.co.nz has the news headline about thunderstorms for auckland area this evening
problem is that is based on 9 hour forecasts and the front has weakened alot over the auckland area this evening...
unless it re intensifies....actaully that cell to the west of northland is lightning active now :)
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by Nev »

treetop wrote:looking forward to intensifying shower activity over western BOP tonight. Usually get NE thunder after 10pm and before 6 am. Fingers crossed ,not a lot of wind with this one which will enhance any thermal activity as the moisture comes ashore and rises.
MS now only have a moderate risk for BoP early tomorrow morn.
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by treetop »

not a lot of red on the radar, still a complex low,where is all the action ? Looks like I will have an uninterupted sleep then
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by Tornado Tim »

treetop wrote:not a lot of red on the radar, still a complex low,where is all the action ? Looks like I will have an uninterupted sleep then
Doesnt need to be red in order for Lightning to occur, echo's are no reflection of a storms overall electrification.

Quite Lightning active west of Northland atm as shown on NZAPStrike :)
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by spwill »

A line of heavy showers coming down the west side of Northland, lightning off shore
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by Manukau heads obs »

that CB to the west of northland might end up still active to the west of here by the morning :)
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by bmo »

Long rumbling thunder heard here.
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by Manukau heads obs »

very heavy rain at one stage here.
Warm night too :)
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by NZstorm »

Some brief very heavy showers here this morning too with 19mm recorded overnight.
My rainfall reading overnight was 29mm, not 19mm. 10mm reading error!
Last edited by NZstorm on Fri 05/09/2014 11:06, edited 1 time in total.
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by treetop »

nothing in Tauranga yet, would have expected heavy showers/storms by now from the NE rather than a band of rain coming in from the NW, odd considering the situation. Maybe as the low moves east and fills there will be more widespread storms ?
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by NZstorm »

Just a note on Saturdays weather.
We will still be under the influence of the upper trough so heavy showers/thunder still on the cards for Auckland/Northland.

500mb chart for Saturday midday.
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by David »

Had a brief downpour here as well around 4.45am, it woke me up. We got 12 mm since 4pm yesterday.
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by Nev »

Yes, nice little downpour this morn.
21.5mm here since late arvo, almost as much as Grey Lynn's 23.4mm.
At 2:52am Lincolnian wrote:Long rumbling thunder heard here.
Looks like you must have got the death throes of that offshore cell early this morn.
Btw, have you moved back to Kaukapakapa now?
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by spwill »

Isolated storms near Ak west coast and the outer Gulf in the early hrs.
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by Nev »

Sparking up east of Coromandel atm, so BoP might be in luck later

Akld also looking good this arvo in this morn's update for today…
MetService - Thunderstorm Outlook

Valid to: Midnight Friday 5 Sep 2014
Issued at: 8:38am Friday 5 Sep 2014

Unstable conditions are expected over the northern half of the North Island today, with convective showers for many areas. Some of these showers are likely to be heavy, with a moderate risk of isolated thunderstorms from about Taranaki and Taupo northwards (including parts of Gisborne and northern Hawkes Bay). The highest risk of thunderstorms is about Northland and Auckland this afternoon and early evening. Any thunderstorms that develop over the upper North Island are likely to produce localised heavy rain with rates of 10 to 25mm/hr and possibly small hail. There is also a low risk of one or two thunderstorms slightly further south this afternoon and evening, as indicated on the chart.

No thunderstorms expected elsewhere.
MetService Aug 5 T-Storm Outlook Map - Is. Aug 5.png
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Re: Unstable low over North Island Thurs 4th to Sat 6th

Unread post by NZstorm »

Sun breaking through cloud layer, temp 18C dp 15C. Can see T/cu out to SE.
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