NZ Summer Weather Outlook

17 12 2010

Wondering what the weather is going to do this Summer and want to optimise your kitesurfing/paddling holiday? Bob McDavitt the Metservice weather ambassador just emailed me some fantastic information in a way that makes sense for me. Hope this makes sense for you as well.  Thanks Bob!

This is a La Nina summer.  To understand the varying impact of La Nina on winds around New Zealand, let us first look at the three normal weather zones in our part of the world.  First, to the north we have the tropics with trade winds that mostly blow from the east. Second, to the south and in the “roaring 40s” we have a zone of disturbed westerly winds and the low-pressure systems of the Southern Ocean.  Third, in between, we have the latitude zone which we see cells of high-pressure take as they migrate from west to east across our weather map- let us call this the “sub tropical ridge”.

These weather zones tend to follow the sun.   The strong cool westerlies dominate our winter and spring when the sun is overhead in the northern hemisphere, and then recede to the south when the sun is seen to get higher in our sky during our summer.  Click on the animation above and watch how the orange belt, which marks the subtropical ridge, shifts from the Australian Bight / NZ latitude belt in summer, to the Australian Desert/north of NZ zone in winter.  This annual solar-driven cycle is so dependable we use it to name our seasons and we track time in years.
The second strongest weather cycle is called the El Nino-Southern Oscillation cycle (ENSO) At present it is in it’s La Nina phase and this occurs when the sea temperatures along the eastern equatorial Pacific Ocean go through an episode of being cooler than normal.  This can last for a year or so and the current event has already been going for six months and should last at least until autumn.

La Nina deflects the normal weather zones southwards around New Zealand.   The subtropical ridge shifted southwards across New Zealand during late spring, much earlier than normal this year, and that helps explains the dry period since Labour weekend and the late November “heat wave”.  This zone is likely to stay in the south until March so that the anticyclones may take a path along 45 South, as shown by the pink arrow in the weather map.  Individual highs may linger around southern New Zealand and the Chatham Islands, producing extended periods of dry sunny weather with light winds around the southwest of the South Island.

Watch the highs on the weather maps and  – when one of them peals off to east of Chathams Island, as shown above, note that northern New Zealand then becomes vulnerable to anything that more form in the tropics to the north.  If a low-pressure system forms north of New Zealand at this time then winds around it may combine with winds around the high like the wheels of an eggbeater, and focus their fury onto a localised area.  This weather map can produce a day or two of wind driven rain and heavy surf, and eastern places between Kerikeri and Gisborne are the most likely targets.

During the coming summer the windscape is, in general (but NOT all the time) likely to favor more than normal wind from between north and east- mainly affecting places northern and eastern parts of the North Island.  With the subtropical ridge lingering over the South Island that is the place where there may be extended periods of sunny dry weather with light winds.

The subtropical ridge should make its way north again around Easter.

Our seasonal weather outlook is also on our rural page ,
at http://www.metservice.com/rural/seasonal-forecast-north-island

Bob McDavitt
MetService Weather Ambassador
Meteorological Service of New Zealand Limited

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Cook Strait Crossing Story- Ali

8 12 2008

Donate to the Westpac Rescue Helicopter at: http://www.fundraiseonline.co.nz/kitethestrait/

Yep we both made it, albeit about 8 nm apart. I’d borrowed Kevs board which was way better than mine would have been but still not quite a floaty as Louis big barge. I struggled a bit in the light winds and couldn’t point as far upwind as Louis so eventually ended up south of Tory Channel, Louis hit the mainland exactly as planned at Perano Head about 4 nm north of Tory
Channel.

Once out of the bay at Makara (total nightmare in light wind dead onshore and lots of kelp) we got good wind for about 40 mins then it dropped to zero and we hung out with kites in the water , the wind came back but it was only about 10 -12 kts , we both had to work the kites but Louis was a bit more efficient and managed to stay on the planned heading. I worked my way slowly south into the shipping lanes regularly hitting 5 knots.

We were about to pull the pin on my trip and the boat was on the way to get me when the wind came back and I got going again. After the ok from the coast guard and quick scurry across the mouth off Tory Channel. I ended up about 500 yrds of the coast up against some big cliffs. The wind started getting funky and I had the strongest gusts of the trip and a couple of lofts then it all died about 100 yards out and I swam to shore.

Meanwhile Louis was in good pressure further north and trying to tack up wind to give him a chance at a quick touch , turn and trip back to Makara. Eventually he touched land at Perano Head and keen for more headed back towards the North Island.

I was way too far south to contemplate the return trip and the cliff landing hadn’t been nice to my gear so the boat came down and picked me up.

Louis was ripping in steady 18 -20 on the way back and we struggled to make ground on him, its way harder work doing 15kts in a 20ft boat in rough seas than it is doing 20kts on a kite.

With the magic of VHF, Spot and Telecom we tracked Louis down 2 hours later – he was about 7nm northwest of Makara. We knew it was 10kts lighter on the Wellington side so he had taken a wide northern circle looking to approach Makara downwind as the wind dropped of. He was making very hard yards of it in about 8 kts of wind when we found him. He persevered for another 1 1/2 hours relaunching every 20 minutes but eventually the kite could not stay in the sky so we pulled the pin 3 nm northwest of Makara.

It was quite cool at times bobbing away by yourself in the middle of the strait waiting (praying) for enough wind to relaunch, but next time I think we will wait for a gruntier forecast.

Ali

Thanks to Dion and Willi for the photos.
http://www.flickr.com/photos/yakers/sets/72157610947914159/

Note: I came across this previous attempt which came close to our experience.