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It’s the classic mix of polar air and warm sub-tropical air out in the Tasman Sea today that’s creating thunderstorms across much of the water and the low that’s causing these storms is moving our way.

The low is deepening today and while many of us across the country enjoy a sunny spring-like day it’s all set to go down hill – dramatically for some.

Head weather analyst Philip Duncan says Taranaki and Nelson are especially exposed to thunderstorms, some heavy tonight and during tomorrow.  “Where the cold air and warm air meet is where the roughest weather will be and that will be Taranaki and Nelson – with New Plymouth most exposed”.  Mr Duncan says downpours may be heavy enough to cause localised flash flooding in some streams and surface flooding across roads however he points out conditions won’t be widespread.  “We’re talking very heavy downpours here and there.  It’s the luck of the draw where these small but severe downpours will exactly take place”.

He says heavy downpours are likely across the west coast of both islands overnight tonight and during Tuesday.  “There could be some squall lines developing – that’s a line of very heavy showers than can deliver gale force winds that come out of no where. Often mistakenly called “mini tornadoes” these squalls simply create a “wall” of wind that can be localised and uplift roofs, fell trees and bring down power lines”.  Mr Duncan says coastal areas in the west are usually most exposed but usually only a handful of properties nationwide are severely affected.

However weak tornadoes – that don’t make it into the traditional measurement of twisters – are also possible.  “We measure tornadoes using the Fujita Scale…usually F1 to F5 (F5 being catastrophic damage).  The ones we typically get in these sorts of systems are often F0 – winds below hurricane speed but can still cause some damage”.

MetService has issued rain warnings for Mt Taranaki and West Coast regions – they can be found in the weather section at MetService is  also advising thunderstorms and “weak tornadoes” may affect some regions – their warnings can be found at 

For the latest lightning strikes please use the free Weather Watch Centre lightning radar on the right hand side of this page.


LJ on 11/08/2008 8:15pm

all back to normal! Raining heavily in the BOI this morning. The last 2 days have been stunning though. Luckily I didn’t plant out my wee seedlings as they would have been frozen solid!

Föehn on 11/08/2008 10:02am

Well, mowing the lawn really. It had got so long with all the wet days that saw the mower snoozing in the garden shed, (the machine that is, not the other half), that I almost needed a compass to find the clothesline. I didn’t quite manage to obliterate the black foot prints left behind by my walk across the frosty grass early on Sunday morning though.

So, now that I have my tomato seedlings under way, is southern Auckland likely to see any more frosts this winter?

WW Forecast Team on 11/08/2008 10:23am

Hmmm that’s a very good question.  Usually our frost season ends as fast as it starts in the City of Sails….I think with another southerly blowing up this weekend/early next week there is still the chance of frosts.  In places like Auckland frosts can be very damaging to plants at this time of year with spring buds/growth taking place.  My entire fence line of Black Taro was wiped out by Saturday’s -2 frost.   I’d say if we don’t get any frosts next week then the chances will start to become heavily stacked against any more frosts for Auckland northwards.

Brendan on 11/08/2008 6:43am

Hi there just asking… this year in Tauranga we having be having frosts… thats not new.. but this year some of them where like powder in the cars at work, not ice. Why is that….

Just asking


WW Forecast Team on 11/08/2008 6:53am

Hmmm…I’d assume it was probably frozen condensation.  Very tiny ice particles.  Same thing happens when drizzle freezes…it can be a very fine white powder – quite common in places that get snow regularly. But in your case I’d guess it was just dew/condensation inside the car.


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