Tasman Low - April 26-28

[Tornado Tim]

Right time for a new thread (Another thread should be made up later on if the forecasted anatartic low looks more likely.)

The Tasman low is developing quite nicely according to MODIS satilites and has showed some very good looking CB's out there.

The latest AQUA satellite pass wasnt too long ago so I have overlaid it with WWLN Lightning data on top.
This low that is shown is expected to Weaken and a new low is expected to develop further south bringing frontal activity to Western areas of both Islands.

GFS has been fairly consistent on the front becoming quite active just before hitting the west coast of the South Island due to forecasted colder and unstable air at 500mb ( just below -20°C at this stage).
SFC Sea temps remain quite warm at around 18° to 19°C, combine this with moisture feeding in from the Northern Tasman and the cold front doing the lifting and forcing on air.

Frontal storm activity seems a bit weak in the western areas of the North Island, however I wouldn't rule anything out at this stage. Coromandel Peninsular could get a rumble of thunder or two from the passing of the front.

[NZstorm]

Frontal storm activity seems a bit weak in the western areas of the North Island, however I wouldn't rule anything out at this stage.

The jet stream will be spreading onto the upper North island Friday so fronts should get some extra support from that.

[NZstorm]

Looks like the front will be crossing the North Island early tomorrow but the stronger forcing will be south of Auckland.

We want to see these systems with colder upper air.

[Michael]

Lets face it just another front.No lightning.Nothing exciting but more leaves in the days of SW flow that follows thats it.Even the rain in the fronts have diminished.

[spwill]

.Even the rain in the fronts have diminished.

May is usually the month of change here, wet season not far away

[Tornado Tim]

The Metservice Thunderstorm Outlook looks good

An active cold front with a band of rain is expected to cross the country on Friday. Heavy rainfall warnings have been posted for the northwest Nelson ranges and the ranges of Westland south of Otira. Thunderstorms are also expected to accompany the cold front as it moves through western areas.

There is a high risk of thunderstorms from western Waikato to Taranaki including far northwestern Nelson from about dawn which are expected to support brief heavy rain and wind gusts of 90-110km/hr. Within this area, there is a moderate risk that A FEW OF THESE THUNDERSTORMS MAY BECOME SEVERE as they move in off the sea bringing with them potentially damaging wind gusts over 110km/hr and the risk of a small tornado.

In a wider area in the west from Northland to Coromandel Peninsula, down to Manawatu, about the outer Marlborough Sounds, over much of Nelson and Buller,and south to about Hokitika, there is a moderate risk of thunderstorms on the front during the morning supporting brief heavy rain, wind gusts of 90-110km/hr and still the possibility of a weak tornado in coastal areas.

Thunderstorms are also possible in southern Westland and northern Fiordland during the morning. The risk drops away further to the east of all these areas as depicted on the map.

Elsewhere, no thunderstorms or significant convection expected.

New Storms are currently developing below the upper jet atm, looks like a nice squally storm setup for western areas.

Wouldnt mind watching the storms coming into the coast but it looks like it will come in at night.

[NZ Thunderstorm Soc]

I'm off to Singapore tomorrow. Should be thunderstorms there as that is the norm for that part of the world but best of luck for thunderstorms for this WE here in NZ.

[Michael]

Photos please too never been there.Enjoy!

I'm off to Singapore tomorrow. Should be thunderstorms there as that is the norm for that part of the world but best of luck for thunderstorms for this WE here in NZ.

[ben g]

oh yeah! the last few weeks have been great, went sailing for 3 days over the weekend and had 3 days of sun! but recently i have been going logging onto interweb then realizing there is no weather/nothing to look at. boring.
huge stack stack of old rimu framing on front lawn needs to be burned, neighbors are starting to look at me funny.

[Tornado Tim]

Front looks quite weak, this always happens. We havnt had a strong cold front in a long time.
There is development on the front but I doubt now that any decent storm activity will occur.

[David]

Just had a very heavy shower here, giving 5.6mm within 15mins

[NZstorm]

Too warm aloft. 500mb temps -14C in late April is not a good number for thunderstorms.

We need to wait for those cold upper level sytems to get into the Tasman for the winter thunderstorm season to kick off.

[Tornado Tim]

Too warm aloft. 500mb temps -14C in late April is not a good number for thunderstorms.

Yes, GFS however wasnt good at picking up the warm air aloft, it had numbers down to -20°C which resulted in higher CAPE and forcing on the front.

A fairly good amount of rain from it through, 7.4mm, however it wasnt heavy, more scrappy than anything else.

[Michael]

Feels like summer here,lots of blue sky and light winds.

[spwill]

Feels like summer here,lots of blue sky and light winds.

It has been a warm day with the dewpoint temperature around 16-17C, temperature up to 22 -23 C.

[Michael]

Well enjoy it while we can for tomorrow will be the exact opposite then replayed again on monday and tuesday after a reprieve on sunday.

Where does BOM get their models from? GFS and ecwmf,show a large anticyclone,bom has it in the tasman all week.

[NZstorm]

GFS however wasnt good at picking up the warm air aloft,

GFS had been modeling 500mb temps -14C for Auckland. About -15C to -16C for Taranaki.
I'm referring to the upper level temps with the front.

Where does BOM get their models from?

UKmet.

[Richard]

luckily the 100kph winds forcasted from this system haven't eventuated...yet.

[NZstorm]

TV1 said the max in Auckland today was 26C. That must be an error.

[Tornado Tim]

TV1 said the max in Auckland today was 26C. That must be an error.

so has TV3, I agree with you, it seems like an error to me.

[Dale]

The front lacked punch. 4am this morning it was raining steadily as I was on the way into work.. 9am it fair opened up and poured down for a while (I work down near the Taramakau Bridge for those who know the area) .. but it still wasn't quite the rainfall expected or talked about. The ranges probably did well as it was where the warning was for I guess. Thunderstorms did not eventuate. It was beginning to look interesting late this arvo but as said at the beginning.. it lacked a bit of ooomph. 35mm since midnight is still nothing to sneeze at I suppose, we have had a fairly prolonged dry period.

[Nev]

Not surprisingly, it appears it was Akld Aero that recorded the 25.9C sometime between 9am and noon yesterday (NE to NW wind change). Ardmore (and Grey Lynn) managed a respectable 23C and 22C for Whenuapai and Whangaparaoa. So it's possible I guess, but Metars suggest temps would've had to spike by about 4C within the hour. Also, going by some of the missing data this week, it looks like the Airport may have had some issues with its temp and humidity readings?

[Manukau heads obs]

a NE wind is a warm wind for the airport, with the whole of the auckland isthmus to warm the air up....

[Michael]

About 1030 yesterday amazing high cloud came across and felt tropical at the time,the ground dried up real quick then.Unfortunately had no camera at the time.

[Nev]

Just comparing yesterday's latest data for Akld Aero with NIWA's Mangere site. I seems Akld Aero's 25.9C was recorded during the hour to noon, when temps apparently ranged from 20.7C to 25.9, before dropping back to 22.3C. Winds had turned NW/WNW a couple of hours earlier. Mangere shows a similar peak at that time, but only with a range of 22.5C to 24.2C.

P.S. Bit of everything here in the last 48 hrs - 7.5mm of mostly drizzle plus the odd light shower, but a fair amount of sunshine as well - 22.2C was my high yesterday.