NIWA Climate Summary

for Autumn 2006

• Rainfall: Extremely high in Northland, Auckland, and Bay of Plenty; extremely low in Central Otago
• Temperature: Near average throughout much of New Zealand
• Sunshine: Sunny in Southland

Autumn rainfall was extremely high in Northland, Auckland, and Waikato, and parts of Bay of Plenty, and extremely low in parts of Central Otago. Seasonal mean temperatures were above average in Auckland, Coromandel, western Bay of Plenty, Nelson, Golden Bay, and parts of Waikato, and below average in parts of South Canterbury, and North Otago. The national average autumn temperature of 13.3 °C was 0.1 °C below normal. However, March was unusually cool, and April was rather mild. Sunshine hours for autumn were near above normal in Southland, and below normal in Golden Bay, and north Canterbury.  The overall autumn climate pattern was dominated by frequent troughs or depressions ('lows') over New Zealand, with more frequent northeasterlies over the lower half of the South Island.

Major Highlights

• The highest temperature recorded during the autumn was 30.2 °C recorded at Ashburton Airport on 14 March. The lowest temperature for the autumn was -5.9 °C at Lake Tekapo on 15 May.
• There were eleven high rainfall events, at least six of which resulted in flooding – the most severe was that of 24-25 April, during which time much of the Taieri Plains including Mosgiel were flooded, as well as the towns of Oamaru and Waitati.
• The highest wind gust for the autumn was 150 km/h from the northwest at Castlepoint on 1 March. Storm force southerlies occurred in Cook Strait on 3 March. Four tornadoes were reported, the most destructive occurring near Waimate on 8 March, destroying a large historic homestead.
• Wintry conditions occurred with a cold southerly outbreak during 14-15 May, with snow closing several high country South Island roads, and the North Island’s Desert Road.

Of the five main centres, Auckland was easily the wettest, but also the sunniest. Rainfall was above average in Auckland, Hamilton, and Christchurch, and near average in Wellington and Dunedin. Temperatures were above average in Auckland, and Hamilton, near average in Wellington and Dunedin, and below average in Christchurch. Autumn sunshine hours were below average in Christchurch, and near average in the four other main centres.

Rainfall

Autumn rainfall was at least 150 percent (one and a half) of normal in Northland, Auckland, and Waikato, and parts of Bay of Plenty. Rainfall was also above normal in Thames, Coromandel, Taupo, Gisborne, North Westland, Nelson, and mid-Canterbury. In contrast, rainfall was less than 50 percent (half) of normal in parts of Central Otago. Totals were also below normal in parts of Marlborough, South Westland, Fiordland, and Southern Lakes.

Temperature

Seasonal mean temperatures were near average throughout much of New Zealand. However, they were above average in Auckland, Coromandel, western Bay of Plenty, Nelson, Golden Bay, and parts of Waikato. Temperatures were below average in parts of South Canterbury, and North Otago.

Sunshine

Sunshine hours were near normal in most regions. However, they were at least 110 percent of normal in Southland, and 90 percent of normal in Golden Bay, and north Canterbury.

Full report

• Full details are in the pdf file at  http://www.niwascience.co.nz/ncc/cs/sclimsum_06_2_autumn.pdf/view_pdf

For further information, please contact:

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.

 

AUTUMN 2006 compiled by Ben Tichborne

'Thanks to Bob McDavitt and Trevor McGavin for providing information and weather maps to help compile this article'.

 

Autumn 2006 was a changeable season, with a number of severe weather events affecting various parts of the country, often involving heavy rain and/or gale force winds. The most significant of these were the southerly storm of early March and the severe flooding, which affected eastern Otago and the Coromandel/Hauraki Plains in late April.

 

MARCH

 

# 1st- 6th - A period of cold, stormy weather (see details below)

 

# 7th - Heavy rain in Fiordland, eg Milford Sound 109mm.  Some heavy downpours also in Northland, eg Cape Reinga 69mm (60mm/3hr); Purerua 87mm/12hrs; Kaitaia 68mm.  Northerly gales about Cooks Strait/Wellington; Mt. Kaukau gusting to 72kt at 7pm.

 

# 8th-9th - Cold front crosses NZ on 8th, followed by cold south to southwest flow, and fresh snow on the mountains. (overnight 9th, a dusting as low as about 700m is visible on North Canterbury ranges near Oxford and Amberley) Thunderstorms in parts of Canterbury, plus a tornado (F1/F2) at Waimate lifts roof and tosses a pig.  Waterspouts also reported north of Dunedin. (8th) Morning hail (9th) in some eastern Wellington suburbs, including the Airport (where slushy hail has to be cleared from tarmac).

 

# 10th/11th - Heavy rain in Fiordland, eg Milford Sound recording 91mm (70mm in 6hrs), West Arm, Manapouri receiving 50mm. (11th) Northwesterly gales about Wellington and at Castlepoint.

 

# 12th - Only 12C max in Dunedin in wake of another cold southerly, which spreads over the North Island during the day.

 

# 13th - Light frosts in some inland areas.

 

# 14th - 30C max in Ashburton, due to warm northwesterly flow.

 

# 15th - Brief period of southerly gales about Kaikoura (gusts up 100kph) with a cold front.

 

# 19th - Southerly change drops temperature from a 22Cmax down to 15C in Wellington in afternoon. This change earlier brings 70kph gusts to Kaikoura briefly.

 

# 20th - Thunderstorms in many parts of North Island, eg 32mm in the hour between 2 and 3pm in Rotorua. Only 13C max in Dunedin and 14C in Christchurch, due to cloud and a cool southerly.

 

# 21st - More thunderstorms in many parts of North Island. 32mm in one hour between 2 and 3pm in Rotorua. Cold 13C max in Dunedin, due to cloud and a southerly flow.

 

# 22nd - Afternoon thunderstorms in many parts of North Island, eg 7mm in 10 minutes in Levin. Another storm in hits Hamilton, including a reported tornado in the suburb of Pukete.

 

# 23rd - Heavy rain in Gisborne and Hawke’s Bay. Gisborne: Mangapoike 1oomm/24hr 145mm/36hr Hikuwai 119mm of which 100mm in about 12 hrs. Gisborne City 82mm 36 hrs. Hawke’s Bay: 24 hrs to 2pm 24th in north, Pukeorapa 112mm,  (due to onshore flow and dynamic lifting)

 

# 24th - Only 12C maximums in Dunedin and Oamaru in a cold southerly flow. Southerly gales about Cook Strait. Period of southeasterly gales in Taranaki causes power cuts in some New Plymouth suburbs. 75kph gusts recorded in Hawera; 70kph at New Plymouth Airport.

 

# 25th - Only 13C maximums in a number of eastern South island places.

 

# 26th-27th - Heavy rain in north of North Island, with a period of northeasterly gales in the far north. Kerikeri college students stranded by raised river near Whangaruru.  Kaikohe records 111mm/24hr, Pinnacles 120mm/24hrs. Rather cold 13-14C maximums in east of South Island. (26th)

 

# 29th - A warm sunny 27C max in Auckland, but only 12C maximums in Dunedin, Ashburton and Oamaru, in wake of cool southerly and cloud cover.

 

APRIL

 

# 3rd-5th - Some thunderstorms in northern and western areas.

 

# 7th - Deluge (18.8mm in one hour) in Palmerston North. City's Centrepoint complex damaged.

 

# 8th-9th - Squally showers in northern and western areas. Severe winds (tornado?) damages roof in Kapiti. Fresh snow on southern ranges, including Milford Road.

 

# 10th - Gales cause some damage in Wellington. Thunderstorms in Wellington and Timaru.

 

# 14th - Auckland International Airport disrupted by fog.

 

# 18th - Winds cause some damage in Waikato.

 

# 19th - Warm 24C max at Dunedin Airport, rising from a 2C minimum. Foggy in the Waikato.

 

# 20th - Warm 26C max at Dunedin Airport, while maximums around 20-24C elsewhere in Otago and Southland. Morning fog in Auckland and Waikato, closing Auckland and Hamilton Airports for a time.

 

# 20th-21st - Heavy rain spreading up South Island West Coast.

 

# 21st - Warm in many eastern areas, with maximums in the low to mid 20s. (26C max in Alexandra)

 

# 23rd - Gusty northwesterlies in Canterbury, eg 80kt gusts recorded at Mt Somers. Dust storm causes crashes near Dunsandel.

 

# 25th-30th - Low pressure system gives heavy rain and flooding to several areas (see details below)

 

MAY

 

# 1st - A warm 25C max in Kaitaia.

 

# 2nd - Some more heavy falls of rain with thunderstorms in north of North Island. Downpours cause localised flooding in parts of Auckland.

 

# 3rd - Some heavy rain in Hawke’s Bay, eg 73mm recorded at Pukeorapa (northern Hawke’s Bay) in 7 hours. Slips close Napier-Gisborne and Napier-Taupo highways.

 

# 4th - Morning frosts in many inland parts of the South Island.

 

# 5th - Heavy showers with scattered thunderstorms in northern half of North Island in a pool of cold, unstable air. Only 11C maximums in Taupo and Rotorua.

 

# 9th - Waterspout near Auckland Harbour Bridge, shown on TV news.

 

# 10th - Morning hailstorm in Dargaville.

 

# 11th/12th - Low forms over and east of South Island, with a cold wet southerly developing on its western flanks. Some heavy rain in parts of Otago and Southland (11th) and Canterbury (overnight 11th/12th) - 66mm in Lyttleton, 41mm at Christchurch International Airport, and 64mm (in 17 hours in Geraldine. Surface flooding in and around Christchurch by morning of 12th. Fresh snow above about 700 metres on South Island high country. Snow also on central North Island mountains on 12th as colder southerly flow spreads over the island behind cold front. The front brings 104mm to Mt Taranaki in the 24 hours prior to 9am 12th.

 

# 13th - Some heavy showers north of about Hamilton. Late afternoon hail in Gisborne.

 

# 14th-16th - Cold southerly oubtreak over NZ with snow on high country of both islands. Heavy snow in Mackenzie country causes trouble for motorists near Burke's Pass. (14th) Milford Road also closed for a time. A pool of very cold air brings snow flurries to low levels on the Canterbury Plains late afternoon of 14th, including snowflakes and sleet reported in parts of Christchurch (where temperatures briefly drop to 1-2C by 6pm). Heavy snow falls on central North Island high country and closes Desert Road early on 15th; snow briefly falling as low as Ohakune and Raetihi. Further snow showers on central and eastern North Island high country through to the 16th, with Desert Road closed again overnight 15th/16th due to ice and snow. Southerly gales about eastern coasts of North Island and Wellington (15th), resulting in InterIslander ferry sailings cancelled due to high seas.

 

# 21st/22nd - Heavy rain in Buller and Westland. Waiho (Westland) records 160mm over the two days.

 

# 23rd - Heavy rain around Nelson (causing some surface flooding and traffic chaos), and in the north from Northland to BOP. Fresh snow on Canterbury high country, including 15cm at Mt Hutt. Evening snow in parts of Mackenzie Country, eg Lake Tekapo.

 

# 25th - Heavy rain in some areas exposed to the north and west. 24 hour totals of 128mm at Franz Josef, 108mm at Cascade Hut (Mt Aspiring National Park), 153mm in Takaka, and 95mm in Kerikeri. Surface flooding around Motueka. Cloud cover following a frosty morning results in low maximum temperatures in Otago and Southland, eg only 4C max in Queenstown, 5C in Alexandra, and 6C in Invercargill.

 

# 26th - Mild northerly flow brings 17C+ maximums in most North Island centres. An unseasonably warm 21C max in Kapiti. 20C max in Blenheim.

 

# 27th/28th - Areas of fog in many areas. Super 14 final between Crusaders and Hurricanes at Jade Stadium, Christchurch (evening 27th) played in thick fog - spectators have difficulty watching the game and seeing the players! Heavy fog also causes disruption to Nelson Airport.

 

# 29th - 23mm recorded at Le Bons Bay between 7 and 8pm, during a spell of heavy rain in a southerly flow. A few thunderstorms in the Waikato and Bay of Plenty.

 

# 30th - Brief heavy rain in Auckland, due to upper level trough.

 

 

MAJOR EVENTS

 

1st- 6th March - A period of cold stormy weather

 

The first few days of March are usually regarded as the beginning of autumn in NZ, but this year it felt like that season had been skipped altogether and the country plunged straight into winter, as an unseasonably cold and windy period affected many areas.  A disturbed southwesterly flow covered NZ from the 1st to the 3rd, bringing showers and increasingly colder temperatures, with snow on the South Island mountains. One cold front moved onto the South Island during the afternoon of the 3rd, followed by much colder southerlies. This change crossed the North Island on the 4th, with the southerly flow becoming very strong. This resulted in severe gales about exposed eastern coasts from the Otago Peninsula northwards through the day, and persisting on the east coast of the North Island through the 5th.

 

Some damage was caused the gales in Christchurch (trees uprooted) and Wellington, while ferry passengers had a very rough trip across Cook Strait in 8-10m swells. (Several subsequent sailings were cancelled) 113kph gusts were recorded at Lyttelton, Kaikoura gusted to 137kph, Kaukau to 142kph, and Mana, Wellington reached 128kph. Wellington Airport recorded 109kph. Squally showers and hail also affected many eastern areas, and fresh snow fell on the mountains, including the Tararuas, while flurries were even reported at the summit of the Desert Road. The Taupo Ironman competition was cut short due to the cold gusty southerlies.

 

The flow turned southwesterly on the 5th, but the weather didn't settle down much, as another cold front crossed most of the country. Compressed westerlies just prior to the front saw the Takapau Plains gust to 73kts (135km/h) between 10-11pm, while Castlepoint reached 74kts(137kph).  Southwesterly gales affected coastal Southland and Otago, and also the Nelson area for a time. (damaging some crops in the latter area)

 

Mean sea level pressure analyses for midday NZST 1st March to midnight 5th March 2006 NZST in 12 hour steps are shown here.

 

 

 

 

 

 

 

25th-30th April – Low-pressure system gives heavy rain and flooding to places

 

A complex low developed in the Tasman Sea on the 24th, deepened, and then positioned itself off the South Island West Coast by the 25th. Rain spread to many parts of the country on the 25th, making for wet Anzac dawn parades in many centres. A downpour caused flash flooding on the North Shore. An easterly flow strengthened over the South Island, bringing persistent rain to eastern areas on the 25th. This was initially welcome, as these areas had received little rain for some time. However, the rain became torrential in eastern Otago during the evening, and persisted through the 26th, resulting in extensive flooding, the worst affected areas being Oamaru and the Taieri Plains, where some homes had to be evacuated and roads closed. In the Central Otago/Southern Lakes area, the rain wasn't so heavy, but cold air undercutting the rain band resulted in an early dump of snow on the high country. Motorists were stranded on the Lindis Pass, but skifields received decent falls, eg 40cm at Cardrona.

 

The low moved northeastwards on the 27th. During the afternoon and evening, a band of heavy thunderstorms spread onto the upper North Island. The Coromandel and Hauraki Plains were especially hard hit by heavy rain (such as 175mm at Hahei in three hours!), resulting in severe flooding in many places. Golden Cross Mine near Waihi recorded 293mm in the 24 hours 10am 28th; Paeroa 117mm to 10am 28th (including 24.6mm from 1-2am Friday morning) Thunderstorms continued through the 28th and 29th in many northern areas, including Auckland (28th) Wet weather contributed to a slip which damaged a house at Lake Okareka, near Rotorua. Heavy rain also fell in Gisborne and Hawke’s Bay in the moist easterlies, which persisted through, to the 30th, but not enough fell to cause any significant flooding.

 

Mean sea level pressure analyses for midday 24th April 2006 NZST to midnight 29th April 2006 NZST are shown here.

 

 

 

 

 

 

 

 

CHRISTCHURCH WEATHER - AUTUMN 2006

MARCH

This month is usually classed as the first month of autumn, but this year it felt much closer to winter, as it was much colder than normal with more southerly winds. The first half was dominated by a number of cold fronts crossing. A strong, cold southerly flow affected NZ on the 3rd and 4th, with squally showers and some hail in coastal Canterbury. The winds reached severe gale for a time on the 3rd with some damage in the city. Another cold southerly spread over the area on the 8th, with scattered thunderstorms, including some near Christchurch. (Plus a damaging tornado near Waimate) Snow fell on the Alps overnight 8th/9th; a pool of particularly cold air gave a coating down to about 700 metres on the North Canterbury ranges from Oxford to Mt Grey near Amberley.

During the second half of the month, anticyclones were more dominant at higher latitudes, resulting in cloudy onshore flows. While, there was only occasional light rain or drizzle, daytime temperatures were unusually cold.

APRIL

There was a reprieve from the cold, dull weather of late March in early and mid April, as warmer airflows from between north and west replaced the earlier onshore flows. However, this wasn't to last, as a complex low-pressure system positioned itself over and to the west of the country from the 24th. This brought rain to Christchurch from the afternoon of the 24th to the evening of the next day - unpleasant for Anzac Day parades, but welcome to farmers who hadn't had much moisture for some time. Further rain fell during the afternoon of the 26th and the onshore flow persisting until the end of the month gave some drizzly showers.

MAY

The changeable weather of late April continued through May, with two rainy spells resulting in a wetter than average month for Christchurch with temperatures slightly below normal. thanks to many cold days. In the early hours of the 12th, a period of particularly heavy rain fell in and around the city, causing some flooding. Cold southerly winds (bring fresh snow to the inland high country) briefly reached gale force, but wind and rain eased during the day. On the 14th, cold southerlies brought more rain to Canterbury. A pool of very cold air moved over mid Canterbury during the afternoon bring sleet and snow flurries to low levels, including parts of Christchurch in late afternoon, as temperatures briefly dropped to around 1-2C. Snow settled above about 500 metres on Banks Peninsula. Hail showers commenced in the city in the evening and continued the next day and cold showery southerlies persisted.

Ben Tichborne