New Zealand Weather

[J07]

Spring is slowly on its way. A low to the east is relinquishing its grip, over the next few days an anticyclone centred at 40S will push eastwards, initially directing a showery, cool blast across eastern regions. It will then settle to our east and intensify, predicted to have a central pressure of 1046hPa, then directing light northerlies upon us, strengthening into early next week.

It looks like a dry, warm and sunny period will start once the showers have passed. With day length increasing fairly rapidly and the sun strength in accordance, this will be great conditions for drying out the ground. Many areas have had big rains over the last 6 weeks. Some parts of Canterbury got 6 months rainfall in a month. Wellington is pushing for its wettest 6 months on record.

The attached image shows rain for Te Awamatu in the Waikato, and how it has gone from drought in summertime to getting sodden in mid/late winter.

Over the last two days, 20C has been reached and sea breezes have been picking up in certain areas. Also significant thundery activity on sea breeze convergences and passing troughs.

A sure sign that more springlike times are approaching.

On the sun front, as we move into the last weekend of winter (for convenience....though I prefer using equinoxes/solstices to define my seasons) the UVI will be over 4 under clear skies in the north. By the time September 21st rolls around, it will be a matter of course to dab on the sunscreen and watch yourself outside. A routine that sadly (or maybe not) will persist until mid April.

A warm and gusty first day of Spring is promised.....typical conditions for that time of the year in these parts. However, there is little doubt that cold outbreaks will occur right into November, and beyond if it's a bad year.

But one thing the fickle climate cannot change - the longer days and the scorching sun. Bring them on, I rather think I've had a gutsful of "winter" for the time being!

[Kiwi]

Spring... then summer..... I'm jealous. :o

Where are you Jo?? I remember many a summer day lazing on the beach at Mt Maunganui, and then after we moved, up at Waipu.

It's just constant dreary autumn here!! :o

[J07]

Spring... then summer..... I'm jealous. B)

Where are you Jo?? I remember many a summer day lazing on the beach at Mt Maunganui, and then after we moved, up at Waipu.

It's just constant dreary autumn here!!

Well certainly not as exotic as those places.....or as warm.......Wellington.

I guess at least there's the mountains!

[Kiwi]

Well certainly not as exotic as those places.....or as warm.......Wellington. B)

I guess at least there's the mountains!

Wind, earthquakes.......

potentially quite exciting!?

and both the Rimutakas and Tararua range are no doubt very scenic ... though I've not been there myself

[J07]

Wind, earthquakes.......

potentially quite exciting!?

and both the Rimutakas and Tararua range are no doubt very scenic ... though I've not been there myself

Yeah, I look at them every morning, beautiful really. The Tararuas at the moment have quite the depth of snow above about 1300m. Avalanche warnings in force there....the first for 80 years!

Rimutakas get the odd dusting but it rarely looks the same because they are bush clad pretty much to the tops (about 1000m).

[J07]

From weatherzone, synoptic prog for this coming Friday.

Something distinctly "summery" about that. Look at the progression of the mid-latitude high pressure belt, all centred around 40S, classic summer pattern.

However, looking more closely you can tell it ain't summer! Namely, no monsoon trough, no heat lows on Australia and the fact that there's actually rain possible for Perth!

Sunny here on this "final day of winter", a max of 15C likely. First day of Spring tomorrow, looks to be sunny, dry with gusty northerlies and a high of 14C.

[J07]

AN AMAZING HALF A METRE OF RAIN LIKELY IN THREE DAYS

MetService forecasters advise that heavy rain on the ranges on the South Island West Coast ranges could total in excess of 500 mm this week.

"An active front with intense northwesterly winds is expected to linger over the South Island for several days", commented MetService Weather Ambassador, Bob McDavitt. "The movement of this front is blocked by an intense anticyclone lying to the east of New Zealand. This anticyclone is extremely unusual - today, the barometric pressure reading at Chatham Islands reached an all time high of 1044 hectoPascals."

In southern Westland, a prolonged period of heavy rain between Tuesday and Thursday may produce in excess of 500 mm in the mountains. A good proportion of this rain may spill over onto the eastern flanks of the Southern Alps, meaning those who are planning to camp near Canterbury and Otago rivers and collect whitebait will find quickly rising river levels.

Besides the rain on the West Coast, people in Canterbury, Otago, and Southland are also advised that windy northwesterlies are likely to reach a strength that may damage trees, power lines and insecure structures at times today in some exposed inland places.

Whilst a high pressure centre of 1048hPa (forecast to hit 1049hPa) may be fairly routine to the east of the UK in winter, this one is over the ocean and has no surface effects contributing, it's purely a synoptic beast, and what a beast it is.

As you can see, UVI 5 isopleth is pushing southwards a fair bit already. In a few weeks time, sunscreen will be routine unfortunately.

[J07]

Well it has been a frustratingly grey week. All thanks to....yes, you guessed it- Australia! A low spawned off their east coast, barrelled along in the subtropical jet stream then lost any upper air support, stacked, stalled and basically left trouser leged us off for days on end. There has been thundery activity up north at least.....and it has been warm, with high teens commonplace and 22C reached one day.

However, I'm tired of it....and so is the system, it's leaving us in peace at last. A bit of mess to clear up tomorrow then ridging from Saturday as a high pushes in from the northwest, keeping us dry, warm and sunny until next Thursday.

And with significant improvements in the strength of the sun, it should be a cracking time!

As can be seen from the attached- Paraparam (Wellington) recorded UVI = 4.5 yesterday, slightly higher than predicted. The UVI5 isopleth should be over us soon enough, so saturday - wednesday should be good days for building up an early Spring tan before the sun does its trick and starts frying everything in its path come late October!

As much as I look forward to summer, I do not like the 5 months of dangerously high UV levels which make it impossible to enjoy the sun in the same way as I used to back in Europe.

[J07]

This week has "settled" into a blocked pattern of high pressure across the North Island and gale northwesterlies slamming into the south of the South Island. The orientation of the high has nicely set this up.

The NW winds have got down to the surface at times and seen temperatures rocket and humidities plummet, with RHs of 15% seen in some places.

I mentioned on the weekend that we may see 25C this week but did not really expect it. However, today it was pulled off. That is the warmest temperature, I believe, since April.

A change to southerly conditions will occur tomorrow, so daily highs will drop by as much as 15C. But this pattern looks like it may repeat itself with a dry weekend ahead with another trough coming in behind it, bringing those warm NW'ers.....

In terms of sun strength....

Clear sky UV indices now reach 5 over the entire North Island.

UVI of 6 are coming into Northland, and also onto the higher ground on the North Island (above 2000m it seems).

So it's fairly similar to the UK in high summer.

The equinox is this weekend, so only a few days to go before the days are longer than the nights, and the sun gets hotter and hotter. Just hope the weather behaves itself now that Spring has come for sure! (Unlikely!).

[J07]

Such a classic Springtime pattern we're under at the moment. High pressure just to our North, changing orientation to direct Westerlies or Northwesterlies over the country. The east of the country is going to dry out like mad this week with the warm and dry foehn winds. The incoming troughs won't give anything to those east of a decent range.

Todays high was 23C, but only 15C here. Typically windy for early Spring, a gust of 73mph recorded in the city.

[J07]

There have been very strong northwesterly winds all day today. They occured due to a blocking high to our north and ahead of a cold front pushing over the country. The terrain of the country has accentuated the gales, with the north and south of the South Island bearing the brunt of air being forced around the Southern Alps. This sort of situation always puts Wellington in the firing line. We've had 70mph gusts all day in the city itself, but fortunately it is a place designed to handle high winds (and earthquakes too). You don't tend to see tree branches felled, and the power is never cut out. There are a lot of trees but despite their ferocious roaring they withstand the winds quite well usually.

Issues are on the hilltops. The only road from Wellington to the Wairarapa, which many people commute along daily, is under police advise to not be used. This is due to 90mph gusts that have been afflicting the summit (600m ASL all day).

Now after the cold front, the winds change and ease, but also there is a sharp contrast between different air masses. In the image attached you can see that Timaru is very warm, at 9PM, and also very dry. Whereas Oamaru is 11C cooler and damp. Timaru is under a different airmass (ahead of the cold front), but more importantly there is clear foehn warming and drying in place, which makes the rapid southerly change even more dramatic.

Todays high confirmed as 27C in Timaru. The warmest temperature NZ has seen since April 15th. Roll on Spring!

By the end of this month, we will be seeing clear sky UV indices of 6. Northland is already well into 7 territory. That is not particularly high, but is getting into the range where you have to start being careful, especially if it's a cool and sunny day.

[J07]

I hate to sound like a Whinging Pom, but I do not want the sun to get any stronger than it is right now. It feels like a small child has a magnifying glass directing the sun at me. Come on clouds!

[J07]

Last weekend was pretty warm, with the first 20C of the season at Wellington's official station (up on a hill), although the valley suburbs had seen 20C back in September.

This weekend was quite reasonable. Yesterday go to 19C, we were one of the warmest places in NZ. Sunny also, with a southerly change coming through at 3PM and a few showers. These things are losing their kick though, it was a pretty dry change.

Today, under a colder air mass we only got to 14C, but with the sun out all afternoon it felt pretty hard going.

Today's NZ high of 21C in Kaitaia.

Interestingly, the UV index recorded at Wellington yesterday was 7.5, which was a bit higher than predicted.

Certainly there's a troublesome kick to the sun now and makes it easy to burn if you miss a patch for sunscreen.

Looks like a Tasman Sea depression is going to spin up on Thursday (not seen one of those for a while) which will give a decent dump of rain to Northland and Bay of Plenty I'd imagine. It's fast moving though and a high will move in for the holiday weekend, although definite reminders that it is Spring, NOT summer! As the anticyclone track is still either just to the north of NZ or over Northland, allowing for Southern Ocean troughs to effect the South Island in particular and putting Wellington back into a windy regime.

[Thundery wintry showers]

One point of interest with regards terminology. In Britain we talk of "southerly plumes" and "northerly blasts" or "northerly outbreaks". I see that in NZ southerlies are usually referred to as "southerly changes" (not "charges"- that was a misreading error!). Is this because of the dramatic change in weather that usually ensues when the southerly sets in?

[J07]

One point of interest with regards terminology. In Britain we talk of "southerly plumes" and "northerly blasts" or "northerly outbreaks". I see that in NZ southerlies are usually referred to as "southerly changes" (not "charges"- that was a misreading error!). Is this because of the dramatic change in weather that usually ensues when the southerly sets in?

I think they're also called Southerly Busters (mostly in Australia).

I can only imagine they ended up with these names because of the general speed with which they encroach, combined with the large temperature and dewpoints changes that result. It's most apparent on the east coast of the South Island because their typical pattern is for a northwesterly flow into a southerly change as the front passes. They also get their highest temperatures just ahead of the cold front because the isobars will be more tightly packed and winds the most gusty. Sometimes Christchurch will have a northwesterly a few hundred metres up (and a few km inland), but a northeasterly at the surface. This creates already a big temperature contrast without even an airmass change.

eg in summer, a northeasterly may give Christchurch something like 20C. An inland suburb may be getting hit with a northwesterly and could be at 32C, a few hundred metres on the hills above Christchurch it may also be northwesterly and about 26C. If the pressure gradient increases as the cold front approaches, the northwesterly may reach the surface in Christchurch, temperature may exceed 30C, and then not too long after (depends on speed of the front) it will change southerly and you may end up with 17C.

The changes sometimes happen very abruptly. 5C in 2 minutes was one example last November, or they may be slower. I know in winter people from these areas always have a feeling that if it's very warm, say 17-20C, they are worried it will snow the next day. That happened a few times this winter (see attached) but I think June 2006 was a serious example of it.

There are similarities with the pattern in, say, Melbourne. I still think that place has some of the most variable weather around. Common temperature changes there in a few hours are greater than what much of the UK will experience over a period of a few weeks under normal conditions.

Whereas the wind ahead of the front in New Zealand is foehn warmed and dried, in Australia it is just hot and dry without anything extra needed, because it comes off the interior. So in something of an extreme example, Melbourne may well hit the high 30s, then with the southerly change a few hours later could find themselves on 15C.

In both countries, of course, the temperatures don't follow the time of day. This year's highest July temperature in New Zealand was a 22C (with dewpoints of -9C) recorded at 2AM (IIRC). Likewise, in summer, Melbourne may find itself with 30C at midnight if the centre of a high moves to their east and directs that hot air over them.

The northwesterly has its lovers and haters. They imaginatively called it the Nor'wester. Probably the greatest problem is that it's so gusty. Mean wind speeds can be very low, but gusts up to 100km/h are not particularly uncommon in exposed parts of Canterbury. Then the wind does not bring any relief to the heat, because it is bringing the heat itself. It's hot and dry, and I suppose if you put yourself inside a tumble drier it would be similar. Also in dry summers it tends to blow topsoil out to sea, which is a nuisance.

In a typical NZ summer, the nationwide extreme for the season will be something between 33C and 37C, it will be on the east coast of the South Island, and recorded with some sort of Northwesterly.

[Thundery wintry showers]

Thanks for that- so it sounds like although NZ on the whole has a smaller annual temperature range than Britain, it's possible to get larger temperature changes over short periods thanks to those sudden southerlies. It's hard to imagine anywhere going from summer temperatures to snow in the space of less than 24 hours in this country, let alone 12C drop in 1 hour!

I imagine that many weather enthusiasts in New Zealand will probably get as excited about these southerly changes as many Brits on N-W get about winter northerlies & easterlies and summer "Spanish plume" events then.

[J07]

Thanks for that- so it sounds like although NZ on the whole has a smaller annual temperature range than Britain, it's possible to get larger temperature changes over short periods thanks to those sudden southerlies. It's hard to imagine anywhere going from summer temperatures to snow in the space of less than 24 hours in this country, let alone 12C drop in 1 hour!

I imagine that many weather enthusiasts in New Zealand will probably get as excited about these southerly changes as many Brits on N-W get about winter northerlies & easterlies and summer "Spanish plume" events then.

On the whole, it's hard to sum it up.

Auckland is the most populous city, it has a very small annual temperature range because it's on an isthmus. One of the few cities in the world to have harbours on both sides. That also means if you live there you are within 30 minutes drive (traffic dependent) of wild west coast beaches and golden sand east coast beaches. But, enough of the tourism, that's all Auckland has going for it. Haha. They probably would get to about 28C max in summer, and about 2C in winter. So a small temperature range, yes. Most people living there would not want warmer summers, it's really pretty muggy and particularly uncomfortable on a daily basis from January to March.

Wellington, well our climate is harder to categorise because it's so hilly. But for the "official" station, 2008 had a max of 29.2C and a min of 1.6C. These will not change this year unless we have a highly extreme December heatwave (pretty unlikely) or a prodigiously cold night (that is just not going to happen). In terms of all-time extremes- the minimum is only -2C (recorded back in the 1920s) and the maximum 33C.

The coldest daily high ever recorded at this official station was 5C. So, it's a very mild climate. I've experienced several weeks (accumulated) of days colder than that in some winters in the UK!

However, take a place like Alexandra (Central Otago, South Island). Their average daily highs are 24C in February and 7C in July. In an average year, you would expect them to reach 35C and fall to -10C, that's a pretty significant range and would not be considered exceptional.

Contrast it with Kaitaia, New Zealand's most northerly and warmest town. Average highs are 25C in February and 16C in July. That's a pretty small range. They are unlikely to exceed 30C in a summer, and probably never fall below 0C.

I could mention Raoul Island, since technically it's part of New Zealand, but no one lives there so it doesn't really count! It has average highs of something like 27C in February and 19C in July or August.

As for sudden temperature changes, I posted in a thread the other day whilst watching South Australia change from a hot northerly to a cool southwesterly. The change was incredible:

12:00 : 38C with dewpoint of -32C (that's a RH of 1%)

12:19 : 29C with dewpoint of 7C

13:00 : 24C with dewpoint of 12C

Now both those first two temperatures are hot to me and you. But that is really a huge airmass change in a very short space of time.

I really think Aussie gets the more dramatic changes, simply because they can source much hotter air than NZ even with foehn winds (IIRC, nowhere in NZ has exceeded 40C since the 1970s).

Back to Alexandra....

Their high on Saturday was 12C, with a southerly, pretty chilly.

Their high today (Monday) was 30C, with a foehn northwesterly.

Yes I'd say that would be fairly unlikely in the UK, though not impossible.

It's also notable because it's the first time this season that somewhere in NZ has hit 30C (first time since March!). I was somewhat hoping it would happen this month (sometimes it does, sometimes it doesn't) so that is good.

Southerly changes provoke interest from enthusiasts in particular on the east coast of the South Island in winter, for obvious reasons.

They also create interest across the North Island because of their ability to kick up thunderstorms.

I think we don't tend to get summertime "Northerly plumes" all that often. We would need a low to stall to our west. Lows in the Tasman Sea are not terribly common in summer (the area is highly favourable for anticyclogenesis). We do get this stuff happen often in winter though. It just results in conditions along the lines of highs of, say, 18C in the north with dewpoints of about 16C and leaden grey skies.

We would get the equivalent if a slow moving mid latitude high (common in summer) passes over us and gets very slow moving to our east, directing very warm northerlies across the country ahead of a possible Southern Ocean trough, or an ex-tropical cyclone.

This does happen a fair bit, but it's really, for us, the slow anticyclone to the east that is most crucial. It's pretty horrible weather, I don't think anyone really likes it. It happened in January this year, as ex TC Funa approached, the high to the east drew down warm humid air and we ended up with disgusting conditions. Wellington was gusting to over 100mph on the hilltops, whilst the temperature in the city got to 29C with dewpoints of about 19C. Dewpoints in some northern areas reached 24C briefly. The worst TT/Td combination I saw was Gisborne which was sitting on 28/22, which is pushing tropical conditions. Yuck.

What the hell am I talking about?

Nice day today, sunny, calm, high of 18C. The sun continues in its unpleasant burniness. A UV index of 8. Oh, how I do *not* crave the days of UVI 14 in summer!

Solar angle at noon was 62 degrees today, the same as in the south UK on the summer solstice. Likewise, the sun angle at noon in the south UK today was (or will be!) 25 degrees, the same as Wellington on the winter solstice.

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

Wow -32 dewpoint and a RH of 1%, thats pretty incredible!

[J07]

Today, Timaru saw 29C with dewpoints of -1C. Giving a relative humidity of 14%. Not quite as exciting as 1% but still a pretty dry heat!

[J07]

Interesting day for Kaikoura.

They had the countrywide high of 26C today. At 3PM they were sitting nicely at 23C with 30% RH. Northwesterlies were pretty strong and hot there with gusts up to 65mph bringing in the dry heat.

At 6PM the southerly change had gone through, they fell to 10C with 95% RH. This is not a particulary rapid change by NZ standards (Christchurch had a 12C drop in one hour) but it was one of the windiest. They got a gust, from the south, of 75mph!

Imagine that! All day long you have a strong, hot wind keeping things uncomfortably warm and dry, then you get the southerly change and are assaulted by even stronger gusts bringing in cold, damp conditions.

Sadly, in Wellington we have no foehn winds, so it's a choice today of warm and damp or cold and damp. The front cannot be far off....

Actually it's hitting right now. The wind is blowing Westerly, which never occurs in Wellington except for very brief interludes when it's changing from North to South.

Temperature just fell 1C in 1 minute.

We got the second highest wind gust in the country today with 92 mph. It was pretty windy today, and I even saw some debris about.

.....

Southerly change continues.....

7:37PM - WNW, 13.2C

7:42PM - SW, 11.0C

Nice, 2.2C drop in 5 minutes.

Temperature change is now more gradual, but wind has gone from NW to S in just 9 minutes.

Rain falling at instantaneous rates of 6mm/hr but it won't be sustained.

[Thundery wintry showers]

Possible late snow for the South Island? I see from the GFS outputs that NZ is set to be affected by a very long-draw southerly in a few days' time, coming from the Antarctic Peninsula (mostly via a cyclonic SW flow).

[J07]

We did quite nicely today with 17C, light winds and fine weather. Nationwide high was 24C in Alexandra.

A small high pressure centre was almost directly to our east, one of the few setups where Wellington doesn't get any wind, and also something that is much more common in summer than winter, particularly La Nina summers.

Possible late snow for the South Island? I see from the GFS outputs that NZ is set to be affected by a very long-draw southerly in a few days' time, coming from the Antarctic Peninsula (mostly via a cyclonic SW flow).

Wednesday? It looks to be quite southwesterly, which should restrict snowfalls for the east of the South Island, but Southland and Central Otago look like getting snow surely out of this. Likewise, the higher ground of Westland and Fiordland.

It also will be interesting happenings on the North Island because following the front I'd expect it to be a pretty unstable cyclonic flow with plenty of open cell cumulus, organising itself into troughs and giving some possible thundery activity up there.

I'm watching it fairly closely because if it stays southwesterly then Wellington may get the fabled "fine weather, light winds" combination.

Seems like next weekend there's hints of a low moving in from the west with a fairly slow moving high pushing out east. This could drag down some quite warm and humid air as it slides away. Possible heavy rain falls for northern areas.....

[J07]

Watching this cold snap with some interest.

Could be a disaster for fruit and grape growers in the south. Central Otago hit 25C today........and snow is forecast for them tomorrow.

Looks like being cool for the North Island. Temperatures in the north and east will get into the 20s tomorrow, but only the high teens from then on. It will also be a pretty showery airmass.

Looks as though we'll have a high sitting over the country on Saturday, but that will move off to the east as Sunday progresses. There seems to be uncertainty about what will happen with the low spinning up in the Tasman Sea following on from this. It is increasingly looking like a non-event, however I am not very convinced by the somewhat bizarre SW->NE track it seems to rather spuriously acquire shortly after landfall.

Beyond that, looks as though a fairly broad summer-like region of high pressure is favoured to park over the country aswell as the Chatham Islands and Tasman Sea. However, too far out to be sure about this, and doubtless there will be some troughiness in there that the models don't see yet.

[J07]

Under a pretty tight Southwest gradient today....

Auckland saw classical SW showery conditions, it's never all that pleasant up there in such weather!

Wellington lucked out big time. Blue skies, the odd passing Cu, and gusty northwesterlies couldn't stop the temperature getting up to 17C, which is average for the time of year. The sun also was quite hot.

Dewpoints noticeably lower than the day before (about the only effect the passing cold front had on us) which may help us to a chilly night.

Down south, snow in Invercargill and Central Otago. The frost tonight is of great concern to anyone involved in horticulture.

The warmest places today: Napier, Hastings and Gisborne got to 21C, about average for the time of year.

The coldest places today: Queenstown and Gore got to only 6C, significantly below average.

SW flow looks like continuing until the weekend.

The high progged to be moving in early next week looks particularly broad and stubborn.

Funnily enough, 6th November 2007 also saw shoddy, cold, showery conditions for much of the country. Then Spring was ditched mid-month and summer didn't let up until the middle of April.

It would be nice to have something like that again!

[Selina]

Tornado in Christchurch:

http://www.stuff.co.nz/thepress/4751220a6009.html

No footage but did some damage.