NATIONAL CLIMATE CENTRE                          THURSDAY 6 SEPTEMBER 2007

 

National Climate Summary – Winter 2007: Rainfall and temperature contrasts, with floods, windstorms and tornadoes

 

·                     Rainfall: Well above normal in parts of Northland, Hawke’s Bay, and Otago, well below normal in Nelson, and inland parts of Marlborough and Canterbury

·                     Temperature: Above average throughout the northern half of the North Island, below average over the southern half of the South Island

·                     Sunshine:  Well above normal in Otago and inland South Canterbury

 

The winter of 2007 had contrasts in rainfall and temperature, with significant extremes. There were serious flood producing rainfall events in Northland, Hawke’s Bay, and Otago. Whangarei had its wettest winter since 1973, Nelson experienced its driest winter since 1987, and extended periods of severe frost occurred in Otago. An unprecedented swarm of damaging tornadoes affected Taranaki over 4-5 July. Other windstorms also damaged property and affected infrastructure.

 

Seasonal rainfall was more than 150 percent (one and a half times) of normal in some eastern areas of Northland, central parts of Hawke’s Bay, and in North Otago. In contrast, rainfall was less than 50 percent (half) of normal in inland areas of Marlborough, and parts of Banks Peninsula. Moderate soil moisture deficits, although not severe, existed at the end of winter in many eastern regions from Marlborough to Central Otago. Winter, overall, was warmer than normal throughout the northern half of the North Island, where temperatures were 1°C above average.  However, temperatures were more than 1.0 °C below average in some inland parts of Otago, and also below average in inland areas of south Canterbury and Southland.  The national average temperature of 8.5 °C was exactly normal. Sunshine hours were well above normal in Otago and inland areas of South Canterbury.  Totals were below normal in the Wairarapa. The overall winter climate pattern was dominated by more depressions (‘lows’), often centred southeast of the South Island, with more frequent southerly flow over the South Island and lower half of the North Island, and more westerlies further north.

 

 

 

Rainfall: Winter rainfall was more than 150 percent (one and a half times) of normal in some eastern areas of Northland, central parts of Hawke’s Bay, and in North Otago, and also above normal in the north of Northland, as well as Thames, Coromandel, and East Otago. In contrast, rainfall was less than 50 percent (half) of normal in inland areas of Marlborough, and parts of Banks Peninsula, and also below normal in Wairarapa, Nelson, many inland areas of Canterbury.

 

Temperature:  Seasonal mean temperatures were above average throughout the northern half of the North Island and 1.0 °C above average in parts of Northland and Gisborne. In contrast, they were more than 1.0 °C below average in some inland parts of Otago, and also below average in inland areas of south Canterbury and Southland.  The national average temperature of 8.4 °C was 0.1°C below normal.

 

Sunshine: Winter sunshine hours and/or solar radiation were at least 115 percent of normal in Otago, inland areas of South Canterbury, Westland, and Southland. Sunshine hours were below normal in the Wairarapa

 

HIGHLIGHTS AND EXTREME EVENTS  

 

·       Temperature

The highest temperature during the winter was 22.4 °C recorded at Rangiora on the 1 June. Dunedin Airport was also very warm on 31 August, recording 22.2 °C, its highest temperature for late winter in records which commenced in 1963. The lowest air temperature for the winter was -15.4 şC recorded at Lauder on 18 July, the lowest there since July 1995. Many other inland South Island locations recorded minimum air temperatures below -10.0 şC during July, often accompanied by freezing fog and treacherous ice.  

 

·       Snowfall

7-9 June:                 Snowfall in Southland and Otago, resulted in power outages, with 5-10 cm of snow accumulating in many areas. 

20-24 June:             About 10 cm accumulated in Southland and Otago (including Queenstown and Dunedin hill suburbs), where roads were icy and treacherous.  Reefton, on the West Coast, had its largest snowfall (about 8 cm) since 1969.

 

·       High rainfall

1 June:                     Major rainfall at Arthurs Pass, with 85 mm.

     29 June:                   Rainfall totalled 130-170 mm in Buller and Westland.

17 July:                     Major flooding in parts of Hawke’s Bay, particularly near Hastings, with further heavy rainfall resuming on the 18^th.

30 July:                     Major floods along the south Canterbury-Otago coast.

8-11 August:             Rainfall at Milford Sound totalled 431mm.

16 August:                Rainfall totalled 107 mm at Kerikeri Airport.

 

·       High winds and tornadoes

7 June:                     Wind gusts as high as 148 km/h were recorded from the west at Castlepoint.

24 June:                   A wind gusts of 148 km/h was recorded from the east at Taiaroa Head.

26 June:                   Gale force southerlies in Cook Strait, with 5m swells, resulted in the cancellation of ferry crossings.

4-5 July:                   Several damaging tornadoes affected parts of the north (Auckland and Tauranga) and west of the North Island. Damage was particularly severe in parts of Taranaki over 4-5 July. The first tornado affected New Plymouth’s central business district, lifting a large part of the roof off a major hardware store and destroying a wall. Other shops and houses were also damaged, along with cars. Trees were uprooted and signs destroyed. On the 5^th, multiple tornadoes affected Taranaki resulting in the declaration of a state of emergency. The township of Oakura was severely affected, with a substantial number of houses damaged.  Other towns such Opunake, Motunui, Stratford, Hawera, Normanby, Oakiawa, Egmont Village, Inglewood, Waitara, Urenui, and Pungarehu were also affected.

 

31 July:                    Another, although small, tornado occurred in Brixton, near New Plymouth,  tipping a truck and trailer unit on its side, and tearing roofing iron off and crumpling a building’s large roller doors.

 

11-12 August:           Gale force northwesterlies buffeted many central and southern New Zealand regions, with several damaged power lines in parts of Otago.

 

·       Combined high winds and flood producing rainfall

10 July:                   A state of emergency was declared in the far north as gale easterlies and heavy rainfall produced widespread severe flooding and landslips throughout much of Northland. Thousands of residents were without phones and electricity, and some had to evacuate. The town of Kaeo was worst hit, and Whangarei was completely blocked off by floodwaters and slips. The same weather system produced damaging winds in Northland, Auckland, and Coromandel which resulted in fallen trees, broken power lines, and other damage. More than 140,000 people were without electricity throughout Northland, Auckland, and the Coromandel. A wind gust as high as 180 km/h was recorded on the offshore island of Tititiri Matangi and 148 km/h at Mokohinau Island, north of Auckland, during this event. 

 

For further information, please contact:

     Dr Jim Salinger  – Principal Scientist – Climate, NIWA National Climate Centre, Auckland,

Tel. (09) 375 2053, or (027) 521 9468 (mobile)

Stuart Burgess – Climatologist – NIWA National Climate Centre, Wellington, Tel. (04) 386 0569, or Geoff Baird, NIWA Communications Manager Tel. (04) 386-0543 or (027) 229 6314.     

www.niwa.co.nz/ncc              Copyright NIWA 2007.  All rights reserved.

 

 

 

 

 

 

NOTABLE WEATHER FOR WINTER 2007

(Compiled by Ben Tichborne with help from Bob McDavitt)

 

Winter 2007 was changeable with a wide variety of weather affecting NZ, including damaging tornadoes, flood producing rains, heavy snowfalls, and severe frosts. A notable feature of this season was the contrast between north and south - the North Island was generally milder than normal (though often unsettled), while many parts of the South Island were colder than average, with severe frosts in inland areas.

 

JUNE

 

# 1st - Heavy rain about and west of the Southern Alps. Warm 22C maximum in Kaikoura. Christchurch reaches 20C, 6C warmer than the first day of summer 2006-7.

 

# 2nd - 22C maximum in Napier and 20-21C maximums elsewhere in east of North Island and in Northland. However, colder southerlies spreading over South Island with fresh snow on the high country.

 

# 3rd - Overnight snowfalls on South Island ski-fields, previously bare after a prolonged spell of warm, dry weather. 25cm recorded at Mt Hutt.

 

# 4th - Frosty start to the day in many parts of South Island, eg -3C minimum in Gore.

 

# 5th - Mild 19C maximums in Gisborne and Napier, but severe gale westerlies further south in east of North Island.

 

# 6th - Westerly gales in the far south, with gusts to 57 knots in Invercargill and 45 knots at Dunedin Airport, also in southern Hawkes Bay/Wairarapa (Castlepoint gusts to 71 knots), causing some trees and power lines to topple.

 

# 7th - 21C maximum in Napier, but severe westerly gales from Central Hawkes Bay to Wairarapa; gusts reaching 80 knots at Castlepoint and up to 100 knots at Kaweka Forest. Very cold southwesterlies in the south of the South Island, with snow showers to low levels in Southland, South Otago, and Dunedin's hill suburbs.  Winds up to severe gale (59 knots in Invercargill; 97 knots at Mid Dome; 62 knots in Dunedin) with thunder and hail in Southland. Only 5C maximum in Invercargill; 6C in Dunedin. Combination of wind and snow brings down power lines and closes roads.

 

# 8th - Very cold southwesterlies continuing in south of South Island, with snow to low levels. Roads again blocked, and power cuts in parts of South Otago. Clinton receives about 20cm of snow. 6C maximums in Dunedin and Invercargill, with gales continuing. (58 knots gusts in Invercargill; 61 knots at Taiaroa Head) Snow also on South Island high country and Alpine passes further north. Some overnight sleet around Christchurch and Canterbury Plains, and light dusting of snow as low as about 300 metres on Banks Peninsula.

 

# 9th - Some further snow showers to low levels in south of South Island. Another chilly 6C maximum in Dunedin.

 

# 10th - 20C maximums in Kaitaia and Kerikeri, but cold further south, eg only 6C maximum in Hastings; 7C maximums in Napier and Taupo, all thanks to cloud cover and rain moving in from the north. Fresh snow on North Island mountains; falling as low as Desert Road.

 

# 11th - Welcome rain falls in east of North Island. Warm 20C maximum in Kerikeri.

 

# 12th - Heavy frosts in many parts of South Island, eg -4C minimums in Timaru and Ashburton. All day fog in Reefton with temperature only reaching 3C there. By contrast, a mild 19C maximum in Whakatane.

 

# 13th - Severe frosts and areas of fog in many inland and southern areas of South Island. -7C minimum at Dunedin Airport. Only 1C maximum in Alexandra; 2C in Queenstown.

 

# 16th - Cold southeasterly flow over NZ, with fresh snow on eastern ranges and high country of both islands.

 

# 17th - Cold, wet weather in east of North Island, with snow on the high country as low as about 600m. (but no roads closed) Low temperatures counter any positive impact of this rain on grass growth.

 

# 20th-26th - Very cold period with heavy snowfalls in the south (see details below)

 

# 27th - Widespread frosts, severe in many places, eg -9C in Invercargill and -8C in Ashburton. Only 4C maximum in Queenstown.

 

#  28th - A very cold day in many parts of the country, as heavy frosts (eg -10C in Invercargill; -9C at Tara Hills, Dunedin Airport, and Ashburton) are followed by a layer of cloud ahead of approaching low pressure in the Tasman Sea.

 

# 29th - Heavy rain develops in many northern and western areas. Persistent rain also causes some surface flooding around Christchurch by evening. -7C frosts at Dunedin Airport and Invercargill. Some light snow followed by rain falling onto frozen ground results in dangerously icy conditions in Central Otago and Mackenzie Country. Only 0C maximum in Alexandra.

 

# 30th - More heavy rain in northern and western areas in a north to northwest flow. 167mm in Greymouth, 160mm at Arthurs Pass, 120mm at Farewell Spit, 184mm at North Egmont, and 105mm at Castlerock (Coromandel Peninsula) Rain causes slip in Manawatu Gorge.

 

 

JULY

 

# 1st - Warm 20C maximums in Gisborne and Kaikoura.  Downpour (12mm) at Wellington Airport about 5pm causes a spate of car crashes. Heavy rain on South Island West Coast, eg 121mm at Cropp up to 6am 2nd.

 

# 2nd - Thunderstorms in north and west of North Island and northwest of South Island.

 

# 3rd - Northwesterlies result in 250mm being recorded at Angle Knob, Tararuas in the 42 hours up to this date.

 

# 4th-7th - Unsettled period, including damaging tornadoes and cold outbreak. (see details below)

 

# 8th - Widespread severe frosts, eg -9C minimum in Twizel, -8C at Dunedin Airport, -6C in Christchurch, and -7C in Invercargill.

 

# 9th-12th - Damaging winds and flooding in north of North Island. (see details below)

 

# 13th-20th - Prolonged icy spell continues over inland parts of South Island. -10C minimum at St Bathans on 13th and -4C max there on 16th. Lowest recorded air temperature is -11C at Tara Hills on 18th. -1-1C maximums in Alexandra during this period under freezing fogs. Icy conditions on roads, but freeze is good for those into curling, as ponds have good ice cover for the sport.

 

# 15th/16th - More heavy rain in Northland and Coromandel Peninsula. Amounts a lot less than those of the big storm a week earlier and not enough to normally cause significant disruption, but saturated ground results in more flooding as well as disrupting the clean up from the earlier storm.

 

# 17th-19th - Heavy rain causes flooding in Hawkes Bay and later in parts of Gisborne area. Some homes in Flaxmere and Maraekakaho (Hastings area) had to be evacuated and cars abandoned. 75mm is recorded in only 3 hours just west of Hastings on 17th.

 

# 20th - Some heavy rain in Bay of Plenty, plus Gisborne and Hawkes Bay ranges.

 

# 21st - Heavy falls of rain in north of North Island. Rain causes slip in Tauranga. Cold southerlies develop over South Island with snow showers to low levels in places, especially inland, where existing frostiness allows snow to settle quickly. (though only light falls) Black ice causes problems on Southland roads by evening.

 

# 22nd - Strong cold southerly flow easing over NZ. Fresh snow on North Island high country; snow and ice closing Desert Road for a time.

 

# 25th - Westerly flow pushes maximums up to 20C in Oamaru and Timaru, and 19C in Ashburton and Christchurch.

 

# 26th - 21C maximum in Kaikoura; 20C in Napier.

 

# 27th-31st - Heavy rain causes flooding in lower South Island (see details below)

 

AUGUST

 

# 1st/2nd - Morning fog (accentuated by moisture from recent rain) in Otago; closing Dunedin and Queenstown Airports on 1st.

 

# 4th - Some heavy showers and thunderstorms in north of North Island. A warm 20C maximum in Whanagarei. By contrast, cold in Canterbury with fresh snow on inland high country, due to moist air moving onto an existing cold airmass.

 

# 5th - 19C maximum in Napier in a mild westerly flow.

 

# 6th - Heavy showers and thunderstorms in areas exposed to west and in central NZ. Early morning lightning strike to signal station in Johnsonville disrupts rail services for a time in Wellington region. Snow on South Island high country, eg Lewis Pass. (where chains are essential)

 

# 7th - More thunder and hail from heavy showers in north and west of North Island. Snow lowering on central high country from afternoon, closing Desert Road in evening (reopening late next morning) and making adjacent roads hazardous.

 

# 8th - Heavy rain in Fiordland, eg 191mm at Milford Sound.

 

# 9th - Northwesterly gales in Wairarapa and southern Hawkes Bay. Mild 19C maximums in Ashburton and Christchurch in a west to northwest flow.

 

# 10th - Strengthening northwesterly flow over NZ, with gales in exposed areas in lower South Island and southeastern North Island. (150kph gust at Castlepoint.) Warm in eastern areas, eg 22C maximum in Kaikoura and 21C maximums in Gisborne and Dunedin. Heavy rain developing in Fiordland and South Westland and adjacent main divide areas.

 

# 11th - Heavy rain about and west of the Southern Alps. Milford Sound records 284mm in 48 hours; Makarora 105mm in 48 hours. Severe northwesterly gales in inland areas of South Island and lower North Island, eg 83 knot gust at Rock and Pillar; 75 knot gust at Mt Somers. Wind cuts power in Wanaka, and Rimutaka Hill Road closed by 80 knot gusts. 21C maximum in Kaikoura, but cold, wet southerly change spreading onto far south in afternoon, sending temperatures plummeting and snow on the hills.

 

# 12th - Heavy showers and thunderstorms in north of North Island. Lightning splits a tree in two in Auckland. Snow on South Island high country, eg down to about 500m at Mt Somers, Mid Canterbury.

 

# 13th - Snow showers to low levels in parts of Otago, Southland, and Canterbury. Up to 10cm in parts of western Southland, closing some schools. Lighter snowfalls on the Nelson and eastern North Island high country.

 

# 14th/15th - Widespread severe frosts in southern South Island, eg -8C minimums at Mid Dome (14th), and in Alexandra (15th). -11C frost in Invercargill. (15th)

 

#  15th-17th - A period of heavy rain in northern North Island, especially in areas exposed to northeast. 119mm recorded in Kerikeri; 105mm in Kaeo; 96mm at Whangarei Airport; 150mm at Pinnacles. (Coromandel) Northeasterly gales accompanies the rain in some places, eg 47 knot gust at Tutukaka.

 

# 21st - Cold southwesterlies bring light snow showers to southern South Island hills.

 

# 25th - Northwesterly gales in Southland. Northerly gales about Cook Strait.

 

# 26th - 20C maximum in Timaru.

 

# 27th - Some heavy rain in northeast of North Island, eg 72mm at Pinnacles. Warm 21C maximum in Kaitaia and 20C in Whangarei.

 

# 29th - Mild 19C maximum in Blenheim.

 

# 30th - Some thunder and hail in east of South Island in wake of cold front. Westerly gales in Hawkes Bay and Wairarapa, eg gusts up to 59 knots at Takapau; 60 knots at Castlepoint.

 

# 31st - Summery end to winter, with 22C maximums in several Canterbury and Otago places. (including August record at Dunedin Airport)

 

MAJOR EVENTS

# 20th-26th June - Very cold period with heavy snowfalls in the south

 

This period will be remembered for very cold weather and heavy snowfalls in the lower South Island, which caused much disruption.

 

On the 20th, a deep depression (after delivering a second blast of stormy weather to eastern NSW) moved towards Central NZ, with fronts bringing rain to northern and western areas. Over central and southern areas, cloud spreading south ahead of the system followed a frosty night, resulting in cold day temperatures, eg 4C maximum in Alexandra and 5C in Ashburton.

 

On the 21st, while the airmass over southern areas remained cold, the low moved over the South Island. Rain turned to snow in many inland areas, heavy in Central Otago and parts of the Mackenzie Country. Much disruption was caused, including one death when a car fell into Lake Wanaka. Queenstown Airport was closed by snow, while the opening festivities for the town's winter festival had to be cancelled.

 

By the end of the day, the low had moved to the southeast, leaving a southwesterly flow in its wake, and the snow ceased. However, Very cold air arrived in the far south on the 22nd following a cold front, bringing more snow to low levels. The worst areas affected this time were Southland, South Otago and Dunedin, with many roads closed, and power cuts in South Otago. Central Otago received less snow, but it fell onto an existing cover that hadn't melted, so creating more disruption. The southwesterlies covered all NZ on the 23rd, with further snow falling to low levels in the south, along with southwesterly gales. (which lifted some roofs in Invercargill) Snow also fell to low levels on the West Coast and higher parts of the Nelson area - Reefton's 8cm was reportedly the heaviest there since 1969, with a snowplough having to clear roads through the town. The airmass wasn't as cold as it crossed the North Island, but snow fell low enough to close the Desert Road for a time. Gales were widespread, with westerlies gusting up to 59 knots at Castlepoint and Takapau Plains, and southwesterlies reaching 70 knots in Westport.

 

On the 24th, the southwesterly flow was milder, with snow showers confined to higher country in the far south. However, another cold front reached the far south in the evening, bringing more very cold air and snow to low levels. This cold front moved over the rest of NZ on the 25th, with the airflow tending southerly. This meant the very cold airmass now affected eastern areas, with more snow to low levels in Otago, including Dunedin (lighter than previous fall, but still causing disruption), and now also parts of Canterbury. In the North Island, snow closed the Napier-Taupo Highway and Desert Road, dusted the hills around Taupo, and fell as low as about 200 metres in the south of the island. (including the Rimutaka Hill Road, but not enough to close it) Southerly gales and heavy swells through Cook Strait disrupted ferry crossings. On the 26th, the southerly flow eased, with showers confined to east of North Island.

 

Mean sea-level analyses for midday NZST 21^st June to midday NZST 28^th June in 24 hour steps are shown here.

 

 

# 4th-7th July - Unsettled period, including damaging tornadoes and cold outbreak

 

This period was notable for two outbursts of squally thunderstorms and tornadoes in the west of the North Island, (the latter one bringing especially damaging twisters to Taranaki), as well as a very cold southeasterly bringing snow to low levels in the east of the South Island.

 

On the 4th, a complex low pressure system had moved onto the South Island. A cold front and associated thunderstorms crossed the North Island during the afternoon. Tornadoes caused damage in New Plymouth, Auckland (Botany Downs) and Tauranga. The New Plymouth twister was the most damaging, cutting a swathe through the centre of the city. Cold air moved onto the lower South Island, with snow levels lowering in Fiordland and parts of Central Otago. (eg Glenorchy, Arrowtown, and St Bathans)

 

On the 5th, a ridge from an anticyclone to the south of the Tasman Sea started pushing very cold air onto the South Island in a southeasterly flow, with snow lowering to near sea-level in the south later in the day. Meanwhile the low had moved slowly north to lie west of central NZ, with another frontal disturbance moving onto the island in the evening bringing more squally thunderstorms to the west. These were most severe in Taranaki, where a swarm of at least seven tornadoes struck the area. New Plymouth was spared this time, but the twisters caused much damage elsewhere. The small town of Oakura was worst affected, with many houses seriously damaged.

 

By the next day, the low continued to move slowly north, with unsettled weather continuing over northern areas. Yet another tornado was reported, this time in Northland. Further south, the very cold southeasterly flow affected central and southern NZ, with snow to low levels in many eastern parts of the South Island, falls reaching sea-level in some places. The snow was heavy enough to disrupt travel on roads, especially around Dunedin and inland South Canterbury. Depths reached 6cm at Fairlie, 10cm at Waiau (North Canterbury), and 10cm at St Bathans. Alexandra reached only 1C, while most other centres shivered with maximums no more than 4-5C. The snow was quite patchy, though, with only a little sleet and snow reported around Christchurch by early on the 7th.

 

The low pressure system had moved to the far north by late on the 7th, with cold southeasterlies covering most of the North Island by then (some snow fell on the high country, but not heavy enough to cause disruption), while the flow eased and eventually died out over the South Island, with wintry showers clearing in the east.

 

Mean sea-level analyses for midday NZST 5^th to 7th July in 24 hour steps is shown here.