Moist and unstable week starting Jan 27th

jamie · Unread post by **jamie** » Tue 26/01/2016 13:37

I think this period deserves its own thread.

With Ex TC Victor bringing in some very moist air and nothing to sweep the moist air away, we are left with humid and unstable air mass that look as though will be around for about a week. This should lead to daily afternoon showers and storms over parts of the North Island.

spwill · Unread post by **spwill** » Tue 26/01/2016 14:55

Wind flows look like they will allow seabreezes over coming days leading to convergence. Hopefully our weather is not too cloudy, more sunshine = more instability.

Tornado Tim · Unread post by **Tornado Tim** » Tue 26/01/2016 15:15

spwill wrote:Wind flows look like they will allow seabreezes over coming days leading to convergence. Hopefully our weather is not too cloudy, more sunshine = more instability.

Its forecast to be quite cloudy to overcast tomorrow, which will limit to a certain degree the SFC temps, we need a min of 24°C to get sufficient lift if convergence occurs.
Upper level dynamics are limited with this setup also with weak upper level flows, however a good section of the atmosphere is saturated in the afternoon, which means we should get good latent heat release.

So tomorrow its looking like pulsy convection thats going to be hard to identify due to the vast amount of forecasted cloud (due to the atmosphere being mostly saturated), with good potential for significant accumulations of Rain assoc with any showers/storms.

Regarding the Thunderstorm Outlook posted below, they should consider extending the Mod Severe Risk in towards the central Waikato as a number of Models have indicated large enough precipitable water values which would constitute a considerable risk for large accumulations of Rainfall under any resulting showers and storms tommorow.

Metservice wrote:A very warm moist airmass is expected to lie over the North Island tomorrow.Daytime heating and sea breeze convergence is expected to trigger very vigorous convection, especially over the central North Island and in the far north.

In the afternoon and evening there is a high risk of thunderstorms with heavy rain in Taupo, the south of Gisborne, Bay of Plenty, Rotorua and Waikato, the west of Waitomo, Taumarunui and Taihape and about the Hawkes Bay ranges as indicated on the chart. In this area there is also a moderate risk of Severe thunderstorms with localised torrential rain exceeding 40mm per hour. Torrential rain can cause surface and/or flash flooding about streams, gullies and urban areas, and make driving conditions extremely hazardous.

During the same period there is also a high risk of thunderstorms with heavy rain in the west of Northland as indicated on the chart. in this area there is a low risk of localised downpours with rainfall intensities of 25 to 40mm per hour.Rainfall of this intensity can cause surface and/or flash flooding about streams,gullies and urban areas, and make driving conditions extremely hazardous.

There is a moderate risk of thunderstorms with heavy rain over a broader area as indicated on the chart, including the west of Auckland and Waikato.

No other thunderstorms or significant convection expected over New Zealand Wednesday afternoon and evening.

jamie · Unread post by **jamie** » Tue 26/01/2016 21:45

The wording metservice are using is interesting. I don't recall them using the words 'vigorous convection' before.

40+mm/hr is fun to see. Hopefully I can find some of that tomorrow by chance while I'm out and about.

NZstorm · Unread post by **NZstorm** » Wed 27/01/2016 07:03

Latest 4pm surface wind chart showing the convergence. Waitomo/Northland will have good convergence.

Chart shows a prevailing easterly for Auckland. But a west coast sea breeze/outflow boundary could trigger come convection over far west Auckland.

jamie · Unread post by **jamie** » Wed 27/01/2016 07:09

There is a nice clear slot moving this way so I wonder if the sky will clear this afternoon?

ImageUploadedByTapatalk1453831761.423097.jpg

NZstorm · Unread post by **NZstorm** » Wed 27/01/2016 07:19

Thursday still looking unstable with the modeled convergence running from Northland/east Auckland/down to Bay of Plenty. Maybe Auckland will catch something of interest tomorrow, I suspect we will.

spwill · Unread post by **spwill** » Wed 27/01/2016 07:38

The amount of heating today will have an influence on where the seabreezes occur, however the day looks cloudy.

A very warm start to the day given the 21C dewpoint, current temperature 21C

Tornado Tim · Unread post by **Tornado Tim** » Wed 27/01/2016 08:29

This mornings updated Thunderstorm Outlook:

Metservice wrote: Issued at: 8:06am Wednesday 27 Jan 2016

Warm and humid conditions persist over the North Island, with wind convergences likely to trigger slow moving heavy showers over central and northern areas.There is a moderate to high risk of thunderstorms in the afternoon and early evening from Northland and Auckland to northern Taranaki, and across to inland Bay of Plenty and Hawkes Bay, producing localised heavy rain of 10 to 25mm/hr.Some of these thunderstorms may become SEVERE about central and western parts of Northland, and from the southwest of Waikato and Waitomo to the central North Island high country affecting Rotorua, Taupo, Gisborne, Hawkes Bay, Taihape,Wanganui and Taumarunui as indicated on the chart. These thunderstorms may produce localised downpours and torrential rainfall rates of 25 to 40mm/hr and possibly more, and a SEVERE THUNDERSTORM WATCH has been issued. Rainfall of this intensity can cause surface and flash flooding, slips and make driving conditions hazardous. A low risk of thunderstorms extends further south to the south of Taranaki,Wanganui, Manawatu and the Tararua District.

A front lies slow moving over the northwest of the South Island,with a low risk of a few thunderstorms for northern Westland and Buller in the afternoon.

No thunderstorms expected over the remainder of New Zealand.

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And Resulting Thunderstorm Watch:

Metservice wrote: Issued by MetService at 08:12 am Wednesday 27 January 2016
Valid until 10:00 pm Wednesday 27 January 2016
This watch affects people in the following weather forecast districts:
Northland
Waikato
Waitomo
Taumarunui
Bay of Plenty
Rotorua
Taupo
Gisborne
Hawkes Bay
Taihape
Wanganui

A combination of humid subtropical air, and afternoon and early evening wind convergences, are likely to trigger heavy showers and thunderstorms about the central North Island and parts of Northland during Wednesday. These are forecast from Waitomo and southwestern Waikato, across to Taupo, Taihape and the Hawkes Bay Ranges. Note, central and western parts of Northland are also included in this Watch. There is a moderate risk of these thunderstorms becoming SEVERE, producing localised downpours and torrential rain of 25 to 40mm/hr and possibly more. Rainfall of this intensity can cause flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips. Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain.

Note: A Severe Thunderstorm Watch means conditions are favourable for severe thunderstorms in and close to the watch area. People in these areas should be on the lookout for threatening weather conditions and listen for possible Severe Thunderstorm Warnings. Thunderstorm activity should ease later Wednesday evening.

Issued by: Hordur Thordarson

This watch will be updated by: 09:00 pm Wednesday 27 January 2016

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Tornado Tim · Unread post by **Tornado Tim** » Wed 27/01/2016 08:34

Im working in the Raglan office today, but will leave if/when stuff starts to kick off.........
Jamie, Brian, Ricky, Steven and Simon, what are you guys up to today?

Tornado Tim · Unread post by **Tornado Tim** » Wed 27/01/2016 09:03

Man stuff already starting to go up already and its 9AM!

spwill · Unread post by **spwill** » Wed 27/01/2016 09:31

Tornado Tim wrote:Im working in the Raglan office today, but will leave if/when stuff starts to kick off.........
Jamie, Brian, Ricky, Steven and Simon, what are you guys up to today?

As usual I watch things from here and if something interesting occurs or looks like occurring then I head out.

I see Manakau City already on 24C

shovelopikis · Unread post by **shovelopikis** » Wed 27/01/2016 09:40

23.5c taupo area.

Tornado Tim · Unread post by **Tornado Tim** » Wed 27/01/2016 10:32

First storms have fired!

jamie · Unread post by **jamie** » Wed 27/01/2016 10:51

It's a good thing there is no rain over Waikato yet. The longer it holds off the better

David · Unread post by **David** » Wed 27/01/2016 11:09

22C dewpoint here currently, sure is moist out there!

spwill · Unread post by **spwill** » Wed 27/01/2016 12:42

Looking thundery east of Taupo.

Muggy here now, Greylynn showing 27C, dewpoint over 22C

David · Unread post by **David** » Wed 27/01/2016 13:17

Tropical in Howick today, currently 28C with dewpoint at 23C! Not often the dewpoint gets that high

NZstorm · Unread post by **NZstorm** » Wed 27/01/2016 13:35

spwill wrote:Looking thundery east of Taupo.

Lightning showing up west of Taupo through to Taranaki.

Some t/cu around Auckland.

spwill · Unread post by **spwill** » Wed 27/01/2016 14:57

TStorm activity over Northland now.
Some heat showers in the Auckland area

David · Unread post by **David** » Wed 27/01/2016 15:37

Auckland Airport on 16mm in the past hour

NZstorm · Unread post by **NZstorm** » Wed 27/01/2016 15:46

Heavy shower here at Mt Roskill.

spwill · Unread post by **spwill** » Wed 27/01/2016 16:43

I'm near Pukekohe, have heard thunder here, heavy showers around.

NZstorm · Unread post by **NZstorm** » Wed 27/01/2016 16:56

Distant thunder to south. I am in Grey Lynn.

Sandi · Unread post by **Sandi** » Wed 27/01/2016 16:58

Lightning and very loud thunder in manukau

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