Warm humid wet spell

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NZstorm
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Warm humid wet spell

Unread post by NZstorm »

Looks like the whole country will get a dose of some humidity over the weekend into early next week with dewpoints upto 18C in the north and 15C in the deep south. All that moisture should lead to some big rainfall totals in the west of the country from Taranaki to Nelson to Fiordland. Thunderstorm potential looks limited due to particularly warm upper air but we'll see.
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Re: Warm humid wet spell

Unread post by Ryan Thomas »

Christchurch has some warm days ahead with that and a overnight minimum of 17 on Monday!
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Re: Warm humid wet spell

Unread post by spwill »

Min temps over the North should stay above 18C early next week with some high dewpoint air moving in. Shame the humid weather wont hang around as dry cool air moves onto NZ about tuesday.
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Re: Warm humid wet spell

Unread post by NZstorm »

The front on Monday is modeled to have some big wind shear numbers with it which suggests a tornado risk from Northland to Bay of Plenty. Instability still looks questionable though. Early days so one to watch.

Should we believe the CAPE numbers (800+j/kg) on the GFS for Southland Sunday afternoon?

Looks like a cold pool (500mb-30C) crosses the lower South Island Tuesday.
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Re: Warm humid wet spell

Unread post by mattyj46 »

NZstorm wrote:The front on Monday is modeled to have some big wind shear numbers with it which suggests a tornado risk from Northland to Bay of Plenty. Instability still looks questionable though. Early days so one to watch.

Should we believe the CAPE numbers (800+j/kg) on the GFS for Southland Sunday afternoon?
Looks like a cold pool (500mb-30C) crosses the lower South Island Tuesday.
Is that good for thunderstorms? (Sorry still learning about thunderstorms.)
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Re: Warm humid wet spell

Unread post by David »

I see metservice forecasting gale northeasterlies on Monday (damn I have an exam in the morning). Under this moist warm air, seems to be potential for some good rain totals for Auckland. Just what we need at the moment. Can't say I agree with the temperature reaching 23 degrees on wet windy Monday unless the sun shines. :?
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Re: Warm humid wet spell

Unread post by Myself »

Going out on a limb here, but I think we may see dewpoints in the region of 20C in the south on the weekend...
Certainly it will be more humid down there than they are used to.
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Re: Warm humid wet spell

Unread post by Vertigo »

mattyj46 wrote:
NZstorm wrote:The front on Monday is modeled to have some big wind shear numbers with it which suggests a tornado risk from Northland to Bay of Plenty. Instability still looks questionable though. Early days so one to watch.

Should we believe the CAPE numbers (800+j/kg) on the GFS for Southland Sunday afternoon?
Looks like a cold pool (500mb-30C) crosses the lower South Island Tuesday.
Is that good for thunderstorms? (Sorry still learning about thunderstorms.)
put it this way.. on the global scale, its not that high - the US (and eastern australia) regularly gets above 2000. but for new zealand, its quite a good value. cape is, effectively, the potential strength of potential thunderstorms for a given area.
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Re: Warm humid wet spell

Unread post by spwill »

Going out on a limb here, but I think we may see dewpoints in the region of 20C in the south on the weekend...
Certainly it will be more humid down there than they are used to
What about the fohn effect with the Northerly.

Hopefully 20C dewpoints reach Auckland, love tropical air.
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Re: Warm humid wet spell

Unread post by Storm Struck »

It sure is going to be a muggy 3-4 days ahead and quite alot of rain for the west coasts too.
Not sure whether the storms QLD has been having latly will move down as part of Mondays system or not, probly changes as it heads into New Zealands climate being further south.
Tuesday is the day i am watching out for with the change to cooler air with the SW change in the evening could bring some thunderstorm possibilities.
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Re: Warm humid wet spell

Unread post by Tornado Tim »

Why has met-service posted a thunderstorm outlook for the lower SI?
There is no cape there to produce anything it is on its resting level 400.
Lifted index is at 0 which means mostly stable.
Are they just going by the wind change alone to think it will produce a t-storm?
(images are 12 Hours ahead)
Looking at the sat images a quite significant cloud bank is coming in, and that warm front = lots and lots of humidity!
But no sun to lift the moisture up I don't think thunderstorms will eventuate.
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Re: Warm humid wet spell

Unread post by tich »

Should be raining over Chch now, according to 10pm radar, but central city is dry. (though cloudy with high cloud) Some problem with the radar? Anyway rain is forecast away from the western ranges today.
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Re: Warm humid wet spell

Unread post by Manukau heads obs »

probably picking up vertigo (i.e rain that is falling from high cloud but not making it to the ground
or picking up reflections due to waves in the atmosphere or similar
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Re: Warm humid wet spell

Unread post by gllitz »

virga? :-P
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Re: Warm humid wet spell

Unread post by CHCH Weather Chaser »

Yes, the rain radar doesnt always give a completely true indication of what we should be getting. The intensity is true up in the atmosphere but as someone said it doesn't always hit the ground. The radar has cleared now looking at the 1045pm radar now. There may have been a few showers around sumner this morning, it looked to be just away from central city anyways.
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Re: Warm humid wet spell

Unread post by tich »

I since looked up and saw some high level virga. Most of the times I've seen virga in Chch is in southerly or southwesterly flows, and looks like a shower almost reaching the ground.
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Re: Warm humid wet spell

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Had to laugh before MS is forecasting drizzle on Monday for Christchurch with NE gales and 28C the high.
There is no way we would get drizzle with winds that strong, besides the maps i have been looking at suggest a significant spell of rain.
Yes the upper level is reflecting precipitation high up but obviousbly not falling to ground level.
Fresh gusty Northerly kicked in around 11pm last night and has been since, it will be interesting to feel the sun later on with the dew points gradually on the rise.
Low is down to 989hpa off NSW coast already, normally the lows form as they move across interesting.
Speaking of which just watching some of those severe storms QLD got last week incrediable winds watch this video right through.
http://www.youtube.com/watch?v=skrnDGl1LxQ
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Re: Warm humid wet spell

Unread post by Tornado Tim »

Some thunderstorms to the north of NZ.
I wish it was more south! :(
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Re: Warm humid wet spell

Unread post by Manukau heads obs »

ops, meant virga....was too early in the morning!
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Re: Warm humid wet spell

Unread post by Myself »

spwill wrote:
Going out on a limb here, but I think we may see dewpoints in the region of 20C in the south on the weekend...
Certainly it will be more humid down there than they are used to
What about the fohn effect with the Northerly.

Hopefully 20C dewpoints reach Auckland, love tropical air.
Still was under an enormous lump of warm, humid air in this pretty large warm sector and the south was the first to get it. I thought the drying by the foehn wind would be lessened by it being a straight northerly rather than northwesterly.
I was a fair bit off anyway, highest dewpoints I have seen is 16C in Alexandra and Invercargill.

This whole situation is very interesting to watch. Currently all of NZ is stuck in the warm sector and it looks like hanging around for quite a long time. We are so used to warm sectors passing over in a matter of hours, several days is certainly unusual. It's also giving time for even more warm and humid air to pass down in waves over the country during this period.
I think somewhere will definitely see 20C dewpoints on the North Island so you can get excited! But it will be tomorrow or Monday.
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Re: Warm humid wet spell

Unread post by Myself »

Tornado Tim wrote:Why has met-service posted a thunderstorm outlook for the lower SI?
There is no cape there to produce anything it is on its resting level 400.
Lifted index is at 0 which means mostly stable.
Are they just going by the wind change alone to think it will produce a t-storm?
(images are 12 Hours ahead)
Looking at the sat images a quite significant cloud bank is coming in, and that warm front = lots and lots of humidity!
But no sun to lift the moisture up I don't think thunderstorms will eventuate.
If you squint a bit at the Invercargill 00Z sounding, put the surface values to something like 23/16 then you do get some instability.
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Re: Warm humid wet spell

Unread post by Storm Struck »

Some rather impressive virga cumulus in the sky at the moment, looks almost like mamatus does except more flattend out.
A few scatterd spots of rain too putting a real humid damp smell in the air, and ive noticed some weak CU hanging about under this upper level to the W-SW at the moment too.
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Jason.
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Re: Warm humid wet spell

Unread post by David »

Looking quite interesting with Auckland in the high confidence warning area now too:
severeweatheroutlook221108.gif
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Re: Warm humid wet spell

Unread post by NZstorm »

Looking quite interesting with Auckland in the high confidence warning area now too:
Would be nice to get a decent soaking for the garden. These types of systems can become big rainfall events in the north if you can get the instability going in them but currently it doesn't look like its going to be unstable enough despite dewpoints of 18C on Monday. 500mb temps -9C! But we'll see. Upper level wind fields on Monday look impressive with 850mb 60kts modeled for Auckland.

Models are showing some thundery promise for later next week for northern NZ.
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Re: Warm humid wet spell

Unread post by NZstorm »

Jason, that is interesting footage on the link. You can see how roofs get torn of buildings with exceptionaly strong outflow winds like that. Those types of storms are common in USA in spring, often labeled HP (high precipitation) supercells.
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