General October Weather

[Cyclone Tracy]

For those who like models and GFS, NOAA yesterday approved the implementation of the GFS upgrade to roll out into production on 25th Jan 2019. Internally it is known as GFS Version 15. In the background it will significantly upgrade infrastructure and physics. To the end user it will bring a better resolution to weather systems that have sharp edges i.e thunderstorms and cold fronts.

[NZstorm]

But there storm cells north of me around Kaikoura

Yes. Bob said there were obvious looking instability, yesterday, to the north from when he went up to his usual viewing spot up on the Port Hills.

On Monday the atmosphere was conditionally unstable. That means surface conditions such as DTH and convergence would need to occur to get a storm.

Tuesday there was less conditional instability but there was better forcing in the way of a southerly buster. Cold 700mb temperatures are often a good clue for convection possibilities.

[NZ Thunderstorm Soc]

Today's set up had the advantage of a strongly forced cold front. Those with local knowledge could see the thunder risk.

Yes, with that I would say, judging by yesterday's performance, a low risk would be applicable for tomorrow night and Sunday night.

[Richard]

NW wind returned during the middle of the day, should keep it warmer overnight hopefully

[NZ Thunderstorm Soc]

Looking dark and bleak Timaru way from here. not thunderstormic tho'

[Richard]

Bright and sunny here with a rather breezy NW wind, but sounds like the cloud is on the way .

[melja]

Stunning day and just hit 23C in Rangiora

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[Razor]

Nudged 25 here at 2pm

[NZ Thunderstorm Soc]

Thick high cloud down here this afternoon, with the bleak cloud down Timaru way moving out to see. Got a few spits from this. Not cold though.

[NZ Thunderstorm Soc]

Some shots of the cloud late this afternoon, here.

[Razor]

GFS suggesting some action weather from mid next week onwards, a couple of Tasman sea lows crossing and stalling? But given the number of misses vs hits lately I'm not holding my breath

[David]

Wonderful Spring day here - sunny skies, fresh 7C start followed by a lovely warm 20C afternoon.

[NZ Thunderstorm Soc]

GFS suggesting some action weather from mid next week onwards, a couple of Tasman sea lows crossing and stalling?

Good

[Richard]

yes starting to look like it might possibly be with a bit of luck be a decent rainmaker.. maybe.

[NZstorm]

According to airport data Kaitaia and Auckland got the high today of 21C.

[spwill]

Cloudier for Ak today but tomorrow looks sunny.

A low system crossing NZ later in the week is something to watch, looks like possible snow for the South Island hill country

[NZstorm]

GFS 850mb temperature anomaly Wednesday 12Z. Yes, at this stage can't rule out some snow on hills for Southland/Otago mid week. May or may not happen depending on overlap between precip/cold air.

The warm air coming onto northern NZ later in week should give us a thunderstorm day.

[Nev]

Came across this video of a funnel cloud in Te Awamutu, presumably on Thursday…

https://www.newshub.co.nz/home/new-zeal ... amutu.html

[NZ Thunderstorm Soc]

Came across this video of a funnel cloud in Te Awamutu, presumably on Thursday…

Yes, I saw that but I thought the item was a bit boring, so I didn't post it, as it had that awful "looking through the curtains", video shot, that comes from Facebook, of the funnel cloud.
Tornados are not rare in NZ. They happen quite often in low and upper low pressure systems that move west to east across NZ, mostly in western and NE areas.

[Richard]

Got love the way they dramatized it too - tornado tearing across the sky. and epic

[Nev]

Agree about the farcical reporting - just thought the video might be of interest.

John, it's the TV companies that add the so called 'curtains' to cell-phone videos shot in portrait format rather than landscape format, presumably as it's more palatable than just having black spaces on either side of your TV (or computer screen).

As for (reported) tornadoes being relatively rare in NZ, the key word is 'relatively', i.e. compared to a lot of other countries - the US by far topping the list with an average of over 1,000 tornadoes reported per year. However, it's claimed that the UK, which has an average of over 30 tornadoes reported each year, has more per square km than the US.

As for what causes tornadoes in NZ, you might find this an interesting read:
https://www.niwa.co.nz/natural-hazards/ ... aland-faqs

[spwill]

The Auckland region being well populated would have a better chance of tornadoes/funnel clouds being noticed/ reported but it has been quiet here last few years.

[Richard]

That's really interesting Nev about the UK getting more per square km than the US. But then think of how many never get noticed/reported on the West Coast of the South Island due to the low population and the low cloud bases that often accompany storms along that coastline.

[NZstorm]

On the topic of Tornadoes, current EU model output suggest an F1 tornado on the cards for the upper NI end of the week.

[NZ Thunderstorm Soc]

EC hinted at a Blocking high in the Tasman Sea next week.
Might be interesting for SW/southerlies changes up the coast of Canterbury to see how useless they may be?