In this second newsemail preview on the December 2006 met Soc newsletter we have three items

1. NIWA’s report on Spring 2006
2. First part of edited diary and weather highlights of spring weather 2006 contributed by Ben Tichborne and Trevor McGavin.

 

 

Spring 2006: Distinctive El Nińo spring with blustery westerlies and south westerlies; very windy at times with stronger than usual east/west contrasts in climate.

• Rainfall: Dry in Northland, coastal Bay of Plenty, Gisborne, Hawke’s Bay, and eastern Otago; wet in the southwest of the North Island, and the west and far south of the South Island
• Temperature: Warm in the east of the North Island and Marlborough; temperatures near normal elsewhere
• Sunshine: Sunny in the northeast of the North Island and southeast of the South Island, rather cloudy in the west of the North Island

Classic El Nińo weather patterns produced a spring with many days of westerly gales over the country, with marked contrasts in climate between western and eastern areas. Significant windstorms occurred in some part of New Zealand on at least ten separate occasions, with blustery conditions on many others. Western areas of the North Island and the west and far south of the South Island had very stormy conditions at times whilst the Bay of Plenty, Gisborne and Hawke’s Bay were relatively dry, sunny and mild.

Windstorms particularly in October and November produced one of the windiest springs in the South Island and southern North Island in the past two decades, with the loss of one life and damage to property including blowing down forest trees. Spring rainfall was only 50 to 75 percent (half to three quarters) of normal in Northland, coastal Bay of Plenty, Gisborne, Hawke’s Bay, and east Otago, with significant soil moisture deficits developed in Gisborne, Hawke’s Bay, coastal Marlborough and coastal Bay of Plenty by the conclusion of spring. In contrast spring rainfall was 125 to 150 percent or normal from Manawatu to Wellington, parts of the Southern Lakes and Fiordland. Sunshine showed similar east/west patterns with extremely high values in parts of the southeast of the South Island, and low totals in the west of the North Island from Taranaki to Wellington. The national average temperature for spring of 12.3°C was slightly warmer than normal, being 0.3°C above average. Spring temperatures were particularly mild in Gisborne, Hawke’s Bay and Marlborough and parts of central Canterbury where these were up to 1°C above average. These patterns were produced by lower pressures than normal to the south and south east of New Zealand, and higher pressures over the north, resulting in much more frequent westerly winds than normal. These produced the drying hot Foehn westerly winds in the east, with frequent rain days in the west, and pushed Lake Wakatipu towards flood levels by the end of November.

• The highest temperature during spring was 30.4 °C recorded at Gisborne Airport on the 13th October. Near or record high September air temperatures were recorded in Dunedin Airport (24.9 °C), Invercargill (23.1°C) and Queenstown (24.3 °C) on the 25th, and at Gisborne (24.9 °C) on the 26th September.
• The lowest air temperature for spring was -5.6 °C recorded at Hanmer Forest on the 11th September.
• High rainfall events were very frequent throughout spring in Fiordland, parts of the Southern Lakes, and Arthur’s Pass on about 20 occasions, and high rainfall events occurred in Auckland, Taranaki, Wellington and Golden Bay. Surface flooding occurred in the Wairarapa, and in Wellington during Labour weekend.
• Severe weather on 1 October produced high winds, attributed to tornadoes or waterspouts, which damaged trees and property in West Auckland. Heavy rainfall and widespread surface flooding occurred on the same day in parts of Auckland City.
• A wind gust of 180 km/h from the northwest was recorded at Southwest Cape (Stewart Island) on the 2nd September, a new record for a wind gust at that site (measurements commenced in 1992). Windstorms were very frequent, with southerly gales occurring through Cook Strait and Wellington on 4th, 5th and 24th of October, disrupting sea and air transport. The many more days of strong or gale force westerly quarter winds produced fallen trees and power lines on 9/10 November in Auckland and Bay of Plenty, and felled trees in North Canterbury on 14 November killing one person.

Of the five main centres, spring was especially pleasant in Dunedin. Dunedin again was easily the driest, and Wellington the wettest. Christchurch was the sunniest. Rainfall was above average in Auckland, Wellington and Christchurch, below average in Hamilton and well below average in Dunedin. Temperatures were above average in Dunedin and below average in Wellington. Spring sunshine totals were above average in Christchurch, and well above average in Dunedin. These were below average in Hamilton and Wellington.

Rainfall

Spring rainfall was less than 75 percent (three quarters) of normal in eastern Northland, Coromandel, Bay of Plenty, Gisborne, northern Hawke’s Bay, and East Otago. Rainfall was near normal elsewhere. Rainfall was at least 125 percent (one and a quarter) of normal in Manawatu, Horowhenua, Kapiti, South Westland, Queenstown area and coastal Southland.

Temperature

Seasonal mean temperatures were slightly above normal for New Zealand overall. These were nearly 1°C above normal in the east of the North Island. They were 0 to 0.5°C in most other areas, and close to average in the west and south of the South Island.

Sunshine

Sunshine totals in spring were at least 110 percent of normal in Gisborne, and from Canterbury to Southland. However, 90 percent or less of normal occurred in the west of the North Island, especially in Manawatu. Gisborne and Dunedin recorded their third sunniest spring on record.

• Full details of the Spring 2006 Climate Summary

At http://www.niwascience.co.nz/ncc/cs/sclimsum_06_4_spring.pdf/view_pdf

Dr Jim Salinger – Principal Scientist, Climate
NIWA National Climate Centre – Auckland
Phone +64 9 375 2053
j.salinger@...

Stuart Burgess – Climatologist
NIWA National Climate Centre – Wellington
Phone +64 4 386 0569
s.burgess@...

Geoff Baird – Communications Manager
Phone +64 4 386 0543
g.baird@...

Acknowledgement of NIWA as the source is required.

 

 

 

 

 

NOTABLE WEATHER FOR SPRING 2006

(Ben Tichborne and Trevor McGavin)

 

Spring is normally a changeable season in NZ, but this one was even more unsettled than usual. While September was notable for unusually warm and sunny conditions in eastern areas (and changeable weather mostly affecting in the west and south), October and November saw wild swings in the weather throughout the country. A wide variety of phenomena occurred, with gales, heavy rain, and heat-waves contrasting with wintry blasts bringing hail and snow to low levels. It might be snowing one day at a certain place, then up to the high 20s there a few days later. One type of weather was largely absent during this period - settled and anticyclonic.

 

SEPTEMBER

 

# 1st - Warm northwesterly flow pushes maximums into the low 20s in some eastern South Island places, e.g. 22C maximums in Culverden and at Dunedin Airport.

 

#  2nd - Northwesterly gales in inland and southern South Island; severe in places, e.g. 190kph gusts at Homer Tunnel. Trees down in northern Southland and Central Otago, and vehicles blown off the road near Lake Tekapo. Worst damage is in Ranfurly, where windows are blown in, and roofs lifted. A number of fires in Otago and South Canterbury. 23C maximums in Oamaru and Timaru under the northwesterly flow, with 21-22C maximums in many other eastern places. Heavy rain in Fiordland.

 

# 3rd - 21C maximums in Alexandra and Blenheim. Timaru, however only reaches 13C (10C cooler than the day before), as onshore northeasterly flow replaces warm northwesterly.

 

# 4th - Warm 23C maximum in Kaikoura; 22C in Christchurch, Ashburton and Darfield. Some heavy rain in Fiordland (94mm at West Homer) and Marlborough Sounds. (97mm at Tunakino)

 

# 6th - 22C maximum in Napier. Some heavy falls of rain in northeast of North Island, e.g. 18mm between 3am and 4am in Whakatane.

 

# 9th - Colder southerly brings light snow showers to high country of Otago and Southland. (9C maximum in Gore) Heavy rain developing in Northland.

 

# 10th - Some heavy rain overnight in north of North Island. Brywnderwyn (Northland) records 90mm in 24 hours since midday 9th. 50mm recorded in Whitianga; 150mm in Te Puke; 110mm in Pukekohe; 80mm in Kaitaia.

 

# 14th - Frosty morning in many areas, e.g. -3C minimum in Waiouru. Frosts affect Hawke's Bay orchards. By contrast, it reaches 22C in Alexandra, due to a westerly flow.

 

# 15th - Warm 23C maximums in Alexandra and Timaru.

 

# 16th - 22C maximums in Ashburton and Lyttelton, but colder, gale westerlies in the far south, with snow on the ranges. 63 knot gust recorded at Bluff. Severe westerly gales also buffet Hawke's Bay and Wairarapa, e.g. gusts up to 52 knots in Hastings and 61 knots at Castlepoint.

 

# 17th - Cold and showery in west and south of South Island with snow on the ranges. Falls to quite low levels in Southland and South Otago, along with hail and southwesterly gales, resulting in lamb losses. Only 6C maximum in Gore.

 

# 18th - Frosts in many areas. Some further snow showers above about 700m in the far south. Fresh snow also on Mt Ruapehu.

 

# 19th - Heavy rain on South Island West Coast, e.g. 107mm at Milford Sound and 50mm at Haast. Warm 22C maximum in Timaru. Gales in some eastern areas and about Cook Strait, e.g. 140kph gust recorded at Castlepoint; 90kph in Ashburton; 140kph in Kelburn. Trees toppled at Mt Somers, Canterbury.

 

# 22nd - 25C maximum in Napier. Heavy rain in Fiordland and South Westland, e.g. 85mm at West Homer and 108mm at Franz Joseph.

 

# 23rd - 25C maximum in Alexandra as northwesterly flow develops over the lower South Island.

 

# 24th - Overnight thunderstorms and heavy rain in Westland and Alps/Southern Lakes; lightning starts fires in Central Otago. 108mm at Waiho, South Westland. Northwesterly gales about Central Otago, causing some damage around Wanaka and Alexandra. Warm 25C maximums in Gisborne and Napier.

 

# 25th - Warm spell continues, with 25C maximums at Dunedin Airport and Alexandra, and 20-23C maximums in many other eastern places and also the north of the North Island. Morning fog disrupts operations at Wellington Airport. Heavy rain and thunderstorms develop in Fiordland.

 

# 26th - Another summery day in Gisborne, with a 25C maximum.

 

# 27th - Fog causes delays at Auckland Airport.

 

# 28th - Some afternoon thunderstorms in Hawke's Bay, Bay of Plenty and Northland.

 

# 29th - Warm, humid air from the north (23C maximum in Kaitaia; 19-22C maximums in other places from Hamilton northwards) results in thunderstorms in Northland, Auckland and Coromandel. Also, an early morning downpour in Levin.

 

# 30th - More thunderstorms in north of North Island.

 

OCTOBER

 

# 1st -6th October - An unsettled period (see details below)

 

# 8th-14th October - A cold snap, followed by stormy westerlies (see details below)

 

# 15th - Heavy rain about and west of the Southern Alps and also the Tararuas. 100mm recorded at Arthurs Pass, where a group of trampers are trapped overnight by a flooding river. (they are rescued the next day) A warm 27C max in Napier in a westerly flow, which reaches gale in exposed places of Hawke's Bay and Wairarapa. (150kph gust at Castlepoint) However, a southerly change brings a sudden drop in temperatures in Canterbury, e.g. from 19C to 9C at Le Bons Bay and 22C to 11C in Timaru.

 

# 16th/17th - Cold southerlies spread over NZ, reaching North Island on evening of 16th. Some thunder and hail in eastern areas of South Island, e.g. Canterbury, and fresh snow on the high country.

 

# 19th - Westerly gales in Southland (gusts reach 97 knots at Mid Dome) and northwesterly gales in many eastern areas. Asphalt lifted by the wind at Mt John, near Tekapo. A beech trees falls and crushes a car in the Christchurch suburb of Fendalton in the early morning. A warm 27C max in Timaru. Heavy rain in Fiordland, e.g. 110mm at east Homer.

 

# 21st-24th - Stormy labour weekend (see details below)

 

# 29th - Northerly gales about Cook Strait, e.g. 66 knot gust at Mt Kaukau. Heavy rain in parts of Central NZ, e.g. Mt Taranaki, and about and west of the Southern Alps. 184mm at Arthurs Pass, 100mm in Rai Valley (northwest Marlborough); 120mm at Angle Knob, Tararuas; 250mm at Dawson Falls, Mt Taranaki. A woman is washed down the flooded Pelorus River, Marlborough, but survives her ordeal. Flooding in parts of Wellington.

 

# 30th - A period of southerly gales in Canterbury overnight and early morning, especially about the coast. 49 knot gusts at Le Bons Bay when it's only 4C at 7am = -8C wind-chill. Gusts up to 64 knots in Lyttelton. Damage to trees leads to power outages around Christchurch and Banks Peninsula. Heavy rain also accompanies the wind on the peninsula. Fresh snow above about 800m on South Island high country.

 

NOVEMBER

 

# 4th - Warm 28C maximums in Geraldine and Ashburton in a northwesterly flow.

 

# 5th - Heavy rain in Fiordland, e.g. 72mm in 21 hours at Milford Sound.

 

# 6th - Chilly 11C maximums in Kaikoura and Timaru and 12C in Christchurch and Ashburton under cloud cover in the wake of cool southerly change.

 

# 7th-9th - Active trough crosses NZ, followed by a wintry southerly outbreak and severe gales in northern areas. (see details below)

 

# 10th - Morning frosts in a number of areas in the wake of previous day's cold southerly outbreak, e.g. -2C minimums in Marlborough.

 

# 11th/12th - Cold front brings a period of northwesterly gales in some eastern areas, (e.g. 78 knot gust at Castlepoint), plus heavy rain about and west of the Southern Alps. (98mm at Arthurs Pass)

 

# 13th/14th November - Violent northwesterly storm with heavy rain and gales. (see details below)

 

# 18th - Heavy rain in central NZ, with flooding in places. A chilly 9C max in Dunedin, due to a damp and overcast easterly flow.

 

# 19th - Cold southerly change spreads over South Island, bringing snow to the high country in the south.

 

# 21st - Lake Wakatipu on flood alert, as a result of prolonged wet weather over recent weeks in the mountains to the northwest of the lake.

 

# 23rd - Thunderstorms with heavy rain on South Island West Coast., e.g. 75mm at Cropp. Heavy rain also on Tararuas. (113mm at Angle Knob) Northwesterly gales developing in inland Canterbury (gusts up to 50 knots at Snowden and 66 knots at Beacon Hill) and Castlepoint. (up to 74 knots)

 

# 25th - Westerly gales in Hawke's Bay result in a truck being blown over.

 

# 26th - Thunderstorms in parts of Southland, Otago and Canterbury, as a front and cold southerly change moves over South Island. More heavy rain on Tararuas (180mm at Angle Knob)

 

# 27th - Afternoon thunder and hail in parts of North Canterbury and Christchurch. (pea-sized hailstones reported) Some thunder and hail also in a number of North Island areas, e.g. Wellington.

 

# 29th/30th - Deepening trough crosses NZ, preceded by strong northwesterly flow on 29th. Gales in some eastern and central areas, e.g. 80 knot gust at Mt Kaukau, Wellington and 43 knot gust in New Plymouth. Truck driver blown over on SH73 near Craigieburn. Heavy rain about and west of the Southern Alps (188mm at Milford Sound; 273mm at Waiho), spilling over into Central Otago. (65mm in Queenstown - Lake Wakatipu levels out at just below 311m above sea-level) Yet more heavy rain in the sodden Tararuas, with 200mm at Angle Knob. Wintry southerlies move onto South Island on 30th, with snow to 400m in the south (brief flurries in Arrowtown) and about 700m in Canterbury high country, with about 3cm snow blanketing Tekapo.

 

MAJOR EVENTS

 

# 1st -6th October - An unsettled period with a deep low crossing NZ

 

Warm, unstable air had already delivered scattered thunderstorms to northern parts of the North Island over the last three days of September (see notes above). On the 1st October, a low in the Tasman Sea pushed an even more active disturbance onto these areas. Auckland was the worst affected, with thunderstorms resulting in heavy downpours and localised flash flooding. There was even a tornado reported in Ranui, West Auckland. Mangere recorded 29mm between 5 and 6pm. (day's total was 87mm) The low remained slow-moving to the west of the North Island on the 2nd, resulting in more thunderstorms and downpours in northern areas. Hamilton had surface flooding, while three houses were evacuated in Birkenhead, Auckland, due to a slip resulting from days of heavy downpours.

 

On the 3rd, the low, now a complex feature, moved east-southeast to cover northern and central NZ. Colder southeasterlies on its southern flank brought heavy rain to parts of central and North Canterbury overnight 3rd/4th. As the low pressure system moved to the east, southerlies rose to severe gale about Cook Strait and Wellington on the 4th, resulting in disruptions to Interislander Ferry services and Wellington Airport, as well as other roads and rail lines where heavy seas washed onto them. Heavy rain also fell about Wellington and the Wairarapa - there was flooding in Carterton and a rail bridge was washed out at Mauriceville, north of Masterton.

 

The low had moved well to the east by the 5th, but it had a sting in its tail. Disturbances from high latitudes resulted in a strong and very cold southerly flow developing over southern and central NZ, with snow lowering to about 500m in the central and eastern North Island. The Desert Road was closed for a time (overnight 5th/6th), and high country farmers reported lambing losses due to the combination and strong, icy winds and snow. Cold southerlies continued through the 6th with more snow showers on the eastern high country, but snow levels rose during the day.

 

Mean sea level pressure analyses for midday NZST 1st October to midday NZST 6th October in 12 hour steps are shown here.

 

 

 

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