It’s a fine day. Isn’t it?

What do we mean when we say the weather is “fine”?

The word fine is often used to convey the positive attributes of something. It is synonymous with good, well, enjoyable.

How are you? I’m fine!
How was the movie? It was fine.
This is a fine bottle of wine.

When we write weather forecasts we define the term fine to mean that the sun casts sharp shadows. If cloud is thick enough to stop the sun from casting sharp shadows then, even if it doesn’t rain, we don’t think that’s a fine day.

However, New Zealand isn’t known as the “Land of the long white cloud” for nothing, and only infrequently is the sky completely cloud free for a whole day. Cloud often comes and goes. So, when writing forecasts, there are a number of questions to be answered when describing the state of the sky:

  • How much of the sky will be covered by cloud?
  • How thick will the cloud be?
  • How will the amount of cloud vary throughout the day?
  • Is there going to be more or less cloud than the previous/coming days?

Our perception of fine weather also varies with the seasons. In the summer months the sun is stronger and even if there is a lot of thin or high cloud it can still manage to cast sharp shadows. Also, if cloud does block the sun for short periods of time we are less likely to notice because the air is warmer; in fact, it might feel like a relief for a short time!  In the winter when the sun is weaker it may struggle to cast sharp shadows, and the day will feel cooler. If the sun is blocked by cloud, even for a short time, then it can affect the temperature more significantly and make you feel colder.

So, when it’s not a clear-cut blue sky day we consider all these things, as well as how the weather will make people feel. Will they feel it was a fine day? Or a cloudy day?

Auckland on a Fine Day. Photo by Joerg Mueller.

2011 – The Weather in Review

 

The temperature trend in New Zealand during the past year can be read from the graph below and tells a story. Last summer was significantly hotter than normal, and several tropical weather systems visited our northern parts in January.

Data taken from NIWA’s monthly climate summaries.

Autumn started normally enough in March and April.  Then blocking led to the dominance of north and northeasterly wind patterns, delaying the onset of winter (and the opening of the ski season) by about three weeks.  This all changed in July – click here for a more detailed explanation from our Chief Forecaster, Peter Kreft – when we experienced the coldest time of the year, with polar outbreaks on 25 July and 14 August to 16 August. Spring started a few weeks late but managed to finish on schedule.  And, of course, there was the deluge that struck Nelson in mid December.

Global temperature measurements currently score 2011 as the tenth highest on record. That data is from the global mean surface land-ocean temperature index. 2011 brought its fair share of global meteorological mayhem. In January Brisbane had its worst floods since 1974, and Brazilian landslides killed 900 people in the mountains just north of Rio de Janeiro. Rain in October eased the drought in the Horn of Africa that had been affecting around 12 million people, but the rain was so intense that it brought crop damage to Kenya. The Monsoon stalled over Thailand in October, taking the lives of 650 people in floods, notably around Bangkok.  On Sunday 18th December, Tropical Cyclone Washi became the deadliest storm of the year with landslides taking more than 1000 lives in the Philippines.

The World Meteorological Organization reports that 14 weather events, each with upwards of US $1 billion of damage have occured in North America during 2011:  heavy snow in February, the most active tornado season on record in April and May, a drought and wild fires in Texas, and the wettest year on record in the east along the Canadian/US Border, culminating in the late August with severe flooding from Hurricane Irene and Tropical Storm Lee.

 In New Zealand, 2011 started with an intense La Nina episode and large anticyclones over Chatham Islands. In the days between Christmas and New Year, an intense storm passed over the country and brought gale force winds to many areas and flooding to the Rakaia area, Pelorus Bridge camp site, Rai Valley, and Aorere River in Golden Bay.

In January there were many episodes of strong easterly winds as three lows of tropical origin brought torrential rain and gales. Former tropical cyclones Vania and Zelia produced heavy rain on the 18th on the West Coast, resulting in the Fox River bursting its banks. On 22nd/23rd, a low which formed near New Caledonia moved towards NZ producing rain that caused slips and road closures over much of the North Island, along with a significant storm surge for Auckland.  Insurance payouts for this flooding were $7NZ million. Also, Tropical Cyclone Wilma moved rapidly across the northeastern North Island on the 28th/29th, and brought severe flooding and slips to northeastern regions of the North Island. Insurance payouts for this were $20NZ million, making it the most expensive weather event in NZ in the past year (insurance payout figures from Insurance Council of NZ: http://www.icnz.org.nz/current/weather/).

MetService Weather Map showing Tropical Cyclone WILMA on 28 January 2011. This was our most damaging storm in the past year.

In February, weather conditions were generally settled.  There was a record-breaking heat wave on Waitangi Day, with Timaru Garden’s 41.3 degrees centigrade topping the list of available temperatures.  It was an extremely dry month in the North Island – the driest February in Dannevirke since records began there in 1951. By way of contrast, central Otago had twice its normal February rainfall.

March was very wet over the North Island and parts of the South. After crossing Raoul Island, Tropical Ccyclone Bune wound down as it passed east of East Cape at the end of the month.

April brought more southeast winds than usual, with wet conditions for eastern areas.  The flooding and slips in Hawke’s Bay on 26-27th April triggered evacuations and resulted in insurance payouts of $6.4million.

During May and most of June north or northeast flow patterns dominated, bringing record-breaking warmth.  Ash clouds from a South American volcano also challenged air travel. May will be long remembered for the tornado that struck Albany on the 3rd, taking the life of a worker.  Insurance payouts for this event were $6 million. On 18th June a landslide took the life of a teenager at Ohope. On 19th June tornadoes hit Taranaki, triggering an insurance payout of around $2 million.

During July and August stormy west, southwest, and southerly flow patterns dominated; click here for a more detailed explanation from our Chief Forecaster, Peter Kreft.  This was the coldest time of the year, with polar outbreaks on 25 July and 14 August to 16 August.  Snow fell across the lower North Island, with flurries in locations well north in the country.

 

MetService Weather map at midnight start of Monday 15 Aug showed a blast of southerly air from Antarctica to New Zealand.

September was characterized by southwest flows and October by northeast flows, with winds less than normal and generally settled weather because of dominant anticyclones.  Most of the Rugby World Cup games were not directly affected by the weather.  It is interesting to note that on 11th September, just 36 hours after calm clear weather for the opening ceremony, a tornado hit within 10 km of Eden Park. Then on 13th September Wellington was coated with hail (MetService tending on Twitter, such was the intensity of the event), and on 14th September winds caused damage in Auckland, Waikato and Bay of Plenty.  On 18-19th October, Dunedin andChristchurch had their wettest day in 18 months.  On Labour Day (24 Oct) wind also caused damage in Southland and central Otago.

During November,anticyclones came south earlier than normal but the frontal systems of spring remained steadfast. As a result, isobars over central New Zealand were squashed closer together than normal, causing many bouts of wind.  This produced drier than normal conditions in the northeast, and cooler and wetter than normal conditions in the southwest. The moisture causing the rainfall that flooded the Grey River in Westland on 21st came from Australia.

In mid-December a major trough stalled for about two days between a low in the Tasman Sea and a large blocking high east of New Zealand.  This brought a deluge of rain to Nelson.

 

MetService weather map for 15th December 2011 showing a front stalled over Nelson.

The most significant falls of rain occurred in the hills behind Nelson and in the lowland areas of Takaka and Richmond. The rain gauge trace seen at Kotinga in the Takaka township measured 423 mm/24 hours, a new record for this site – the previous record of 256mm/24hr was measured in August 1990.  The New Zealand record for 24 hour rainfall is held by CroppRiver at its waterfall (inland from Hokitika), at 758 mm in 24 hours ending 0620 hours on 27 Dec 1989.

 

Rainfall accumulation graph for Takaka (TAN), Kotinga (TSR) and Nelson Airport (NSA). Accumulation of rain is in mm, and timestamps are in UTC (add 13 hours to get NZDT).

 
 

The total rainfall over the country from this trough can be seen in the rain map for the 7 days ending 18th Dec 2011.

MetService rainfall accumulation map for the 7 day period ending 9am on 18th Dec 2011.

The purple areas received more rain than desired, but other parts of the country received enough rain to be useful for filling up water tanks and replenishing pastures and gardens before the holiday break.

In summary, NZ’s weather in 2011 had its ups and downs, and produced some interesting events.

Everyone at MetService takes this opportunity to wish our blog readers a refreshing break at the end of the year, and we look forward to sharing with you our insights into the interesting weather events of 2012.

 

Rugby Weather: French Storm 1961

In August 1961 my Dad took me to see my first test match. All Blacks versus France at Wellington’s Athletic Park, although with hindsight it was more like New Zealand and France combined versus the weather.

Not that wind and rain were a negative for my ten-year-old self. That seemed to be one of the great things about rugby: it was so important that you were allowed to play in the rain. There was even some thought that the muddier you got the better you had played, the more heroic your effort.

With high hopes we settled into our benched seats, four rows back but not much elevation so I missed some of the good bits when everyone stood up. Dad let me know what had happened. Fortunately, we were at the northern half of the ground, almost lined up with the 25 yard line, since the wind confined 95% of the play to that end.

The French had the southerly storm behind them in the first half but after a solid All Black defensive effort it was nil all at half-time. “A twenty point wind” my father told me. In those days rugby’s way of measuring wind strength was how many points it was worth when it was blowing in the direction you were going. If it was blowing side-on it was just irritating.

I felt a bit sorry for the French. Their first trip to New Zealand. It seemed a long way to come to get thrashed. Then the second half started and the French defence proved resolute. Time passed and the All Blacks weren’t scoring. “The wind’s so strong it’s hard to pass”, my father explained. “Blowing the slippery ball away from their hands”, he added. Then the French scored. Length of the field try, against the run of play, not meant to happen, where was the cover defence?

Time running out, France 3 All Blacks 0, the abyss gaped before me. Then Tremain scored in the far corner. That’s what Dad said, I could only see the back of the man in front, though I could feel the hysterical relief in the cheering. Tied up 3 -3, conversion attempt from the sideline regarded as impossible in such a wind. Draw better than a loss, but not much. Then the kick went over, delirium. Don Clark later claimed to have aimed the kick along the 25 yard line and let the wind take it through the posts.

Ten minutes left, time to score again and stamp our authority on proceedings. But the French held on and 5-3 to the All Blacks it finished. The guilty pleasure of a narrow victory as the crowd slowly poured away. My first taste of a moral victory and it wasn’t ours. When we were meant to be piling on the points, the French had scored into the wind through their fabulous running and passing. Something we hadn’t done.

And what a wind it was, 137km/h gust at the airport, trees down, roofs off houses, ships unable to enter the harbour, airport closed, waves breaking over roads and railway lines. One man’s hat blew from Athletic Park to Karori. And the realisation that rugby’s wind scale was circular. As the wind strength picked up a ten point wind might turn into a fifteen point wind, but if the strength kept climbing the needle went right round the dial. A hurricane strength wind favoured no-one and was worth zero points.

Situation map as at 6pm Friday 4 August 1961

Situation map as at 6pm Friday 4 August 1961

 

 

Waikato Stadium Weather

After a week of sunny weather, it appears that rain will dampen Waikato Stadium before this weekend’s Tri Nation rugby game starts there at 7:35pm on Saturday.

Waikato Stadium

Waikato Stadium

This clash between the Springboks and the All Blacks is the first Tri Nations game to be held at Waikato Stadium (capacity 25,800).

If the All Blacks win this game and score four tries and the bonus point, there is still a chance of their winning this year’s Tri Nations.  The game is likely to be played in wet conditions, with perhaps 20mm of rain falling in Hamilton on Friday and Saturday.  This equates to something like 20 litres per square metre  of water  – that’s around 10 tonnes falling on the half-hectare of  playing surface inside Waikato Stadium.

20mm of rain will be worth a bonus point as far as Waikato farmers are concerned. After a week of dry weather, that’s about the right amount of water to keep the soil moisture levels up and running, producing optimum pasture growth.

So if the All Blacks can score two points for every millimetre of rain delivered to Hamilton by this front, we will all be smiling.

Will it be raining during the game? Quite possibly. But with a light northerly and an air temperature of around 12 degrees, it won’t be too cold. Scarves are optional.

When it comes to an important event such as this, you can check out TWO of the weather models we use  here (3-day) and here (7-day). These models have different calculation schemes and treat the physics of the atmosphere diifferently, which is why their predictions don’t always agree. Our skilled meteorologists take these and other data into account to produce a forecast that is the most likely one to replicate the real world.

For Hamilton go here, or for your place go to www.metservice.com and click on your place-name.

Autumn Colours

bobBlogs are a great way to keep up-to-date. From today, several MetService staff will start posting about the weather. Every few days we intend to add something new, commenting on recent weather, or coming weather, or how weather is likely to affect important events, or stories relating to the weather or to places that our job takes us. These posts will generally offer you a chance to share your responses with us all as well, but some of our posts will be coming from shift forecasters who may not always be able to allow responses.  Most of our posts will be shorter than this first one.

As Weather Ambassador I get to watch the weather pattern as it changes from season to season. Click here for our seasonal team’s outlook, which will be next updated on Friday 8 May. We have recently been witnessing, once again, the annual march of autumn colour across the country’s deciduous trees, so I’m making AUTUMN COLOUR the topic of our first blog post and inviting you to post here your own images of AUTUMN 2009.

This change-of-colour amongst the trees moves from south to north in tune with decreasing day-length. The intensity and duration of “autumn colour” depends on the weather as we slide slowly into the darker months.

photosyn

For growth, trees draw on the four basic elements: earth and water (soil moisture), fire and air (sunlight and Carbon Dioxide). During summer the green chlorophyll of leaves takes in water (from rain-fed roots in the earth) and carbon dioxide (from the air) and uses sunlight in the process of photosynthesis to make glucose (sugar) which is used by the tree for food. Chlorophyll appears green because it is a very strong absorber of red and blue light, using this energy for photosynthesis.

photo2

Shorter days in autumn are the trigger for cells at the base of the leaf stem (the abscission layer) to swell and cut off the connections between leaf and tree. Grapes and Kiwifruit also shed their leaves this way so that new ones can grow in the spring. Without fresh water to renew it, the chlorophyll in the leaf stops working and starts decaying. As the bright green chlorophyll fades away, glucose and other products that are left behind start to show their colours.

Orange comes from carotene and yellow from xanthophyll; common pigments that are also found in flowers and foods like carrots and egg yolks. These compounds act as accessories for chlorophyll: they cannot do any photosynthesis themselves but they do absorb green light (which is not being used by chlorophyll) and transfer some of this energy to help the chlorophyll.

image3

The bright red and purple colours come from anthocyanin pigments, which are made from any leftover glucose trapped within the leaves of some trees (e.g. maples and some oaks). These pigments are also found in plants; for example, rhubarb, beets, red apples, and purple grapes, and flowers like violets and hyacinths.

bike

Brown leaf colours come from tannin, a bitter waste product also found in tea leaves.

Each autumn brings a different combination of these pigments and a varying range of colour. The brightest colours are seen when autumn has bright sunny days and cool (but not frosty) nights. Under these conditions leaves can make a lot of sugar as their veins close down, trapping anthocyanin pigments that produce such glorious red and purple hues. Alternatively, if autumn has lots of cloudy days and warm nights then these red pigments are missing and the display is rather drab. An early frost or a strong wind speeds up the fall of the leaves and may bring an early end to the colour of autumn. Soil moisture during summer also has a variable impact on leaf health and hence on autumn colour.

Leaves directly exposed to the sun may turn red, while those on the shady side of the same tree or nearby trees may be yellow.

in-the-sun

So, how does autumn 2009 measure up for colour? A good way to view temperatures for the past few months is offered in the public domain by the Physical Sciences Division of NOAA’s Earth System Research Laboratory. In the first image below a time section is given of the surface air temperature from the latitudes of 35 South (top) to 50 South (bottom). The image covers from March 1st at left to April 30th at right. The daily mean over the longitudes from 165 to 180 East is used, so this image does not show the day/night or west/east variation or the ground frosts. It does show clearly how much Northland (around 36 South) is warmer than Southland (around 46 South), and reveals an almost weekly cycle of warmth and coolness.

air temperatureAir Temperature

(Above) Left: Time Section of surface air temperature over NZ for March and April 2009.(deg K= dec C +273), Right: Variation from normal (blue is cooler and red is warmer). Click images to enlarge.

Time Section images provided by the NOAA/ESRL Physical Sciences Division, Boulder Colorado from their Web site at http://www.cdc.noaa.gov/

To show the variation from normal, the second image gives the temperature anomaly. This is interesting in that there is more blue than red for most of autumn. We mostly attribute that to cooler-than-normal nights due to clear skies in passing anticyclones. The frostiest morning was 22 April when MetService measured a 7 degree frost at Masterton (grass minimum temperature was -7C). There were a few noticeable cold fronts as well: one on 11 March brought light snow to the Remarkables and another on 9 April, just before Easter, brought 20 cm of snow to Mt. Hutt. Generally the winds have been less than normal this autumn allowing the leaves to stay on the trees longer. The warmth since ANZAC weekend has been more noticeable in the South Island than further north.

During February coastal Hawke’s Bay and Gisborne missed out on rain that replenished the soil moisture everywhere else in New Zealand. This is likely to make the timing and brilliance of their autumn colour different from other regions, and maybe noticeably different between hills and coast. I’m not sure what the difference will be, so I’m especially interested in getting replies to this post from people in the eastern North Island.

Click here to read more about how weather affects autumn colour.
park

Thanks to Alan McDougall of MetService’s Media Graphics Unit in Christchurch for contributing these photos taken during ANZAC weekend.
Please login and post your own comments or images of autumn colour here (try to keep each image below 500k in size).