1.   Second part of  weather highlights of spring weather 2006 contributed by Ben Tichborne and Trevor McGavin.

    2.   Ben Tichborne's write-up of how spring 2006 affected Christchurch.

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SPRING WEATHER HIGHLIGHTS (continued...)

 

# 8th-14th October - A cold snap, followed by stormy westerlies

 

After only a brief respite following the previous event, unsettled weather soon returned, delivering another wintry blast and then a spell of much warmer, but very strong westerlies.

 

 On the 8th, a strong west to northwest flow had become established over the South Island, with a cold front moving onto the island. Ahead of it, northwesterly gales developed in the south and later in parts of inland Canterbury in the evening. Gore recorded gusts of 145kph, and at Mid Dome, the wind reached 145kph. In Otago, 1100 homes lost power due to wind damage, while the wind aggravated fires in South Canterbury. Behind the front, cold southwesterlies brought snow down to about 300-400m in parts of Otago and Southland, including Queenstown (Airport operations briefly disrupted) and the Maniatoto (12.5cm snow at Naseby; 3cm in Ranfurly), as well as above about 450m on Banks Peninsula overnight 8th/9th. Hokitika was blanketed by a midday hailstorm on the 9th, in the unstable westerlies prior to the next front.

 

This cold front moved onto the far south later in the afternoon, bringing even colder southwesterlies and snow showers to low levels in the south. This front had crossed the remainder of the country by the next morning, leaving an unseasonably cold southwesterly flow over NZ on the 10th . Snow showers continued to low levels in Otago and Southland, including Dunedin briefly in the morning. (only 7C max there; Tapanui was still only 2C at 1pm) Snow fell to unusually low levels in Buller and Westland, worrying farmers there. Heavy snow also hit the central North Island, closing the Desert Road for a time. Falls of snow were even reported to low levels in some central and southern North Island areas, including the Hutt Valley and Wellington hill suburbs in late afternoon. Taupo recorded only 4C at 1pm. Hail showers were also reported in many areas, including Auckland.

 

This wintry airflow died out on the evening of the 10th, with frosts developing in sheltered areas. Horticulturalists rushed to protect their crops in places like Marlborough and Hawke's Bay, but milder westerly breezes set in before dawn, limiting the intensity of frosts. The westerly flow increased over the South Island during the day, with gales in the far south. A strong westerly flow persisted over much of the country through to the 14th, with gales in the far south and some eastern areas. Locally severe gusts early on the 14th severely damaged buildings at Timaru Boys High School. The winds were at their strongest, however, on the 13th, with severe gales in parts of Otago and Southland (178kph gust recorded at Mid Dome, Southland) resulting in damage and contributing to fires, especially around Dunedin. Temperatures were warm in eastern areas (though a weak southerly briefly dropped them by about 8C in Canterbury on the afternoon of the 12th), with maximums up into the high 20s. Gisborne reached 30C on the 13th, with Alexandra and Dunedin Airport (where it was snowing only a few days earlier!) reaching 29C on the same day.

 

Mean sea level pressure analyses for midday NZST 8st October to midday NZST 14th October in 12 hour steps are shown here.

 

# 21st-24th - Stormy labour weekend

 

Unsettled and stormy weather during Labour Weekend is far from unknown in NZ and this one certainly had its share of inclement weather, especially in the lower North Island, which received another dose of disruptive heavy rain.

 

On the 21st, a warm northwesterly flow covered NZ, ahead of an approaching trough in the South Tasman. Heavy rain fell on the South Island West Coast (94mm at Cropp, Westland in 7 hours), while northwesterly gales lashed Cook Strait, with 71 knot gust recorded at Mt Kaukau. A cold front moved onto the South Island during the day, with a change to colder southerlies and some snow on the southern high country. Dunedin Airport dropped from 22C at 2pm to only 8C by 4pm.

 

The front weakened as it moved further north, stalling over Central NZ on the 22nd. However, a low formed on its western portion in the central Tasman. This low slowly crossed the North Island over the next day to lie to the southeast by the 24th. Heavy rain fell in many parts of the island during this period, e.g. 105mm at North Egmont (24 hours ending 9am 23rd), 109mm in Northern Tararuas (22nd), and 200mm in Wainuiomata. (over the 23rd and 24th) This rain resulted in slips and flooding in areas that have already suffered during recent months. The Manawatu Gorge was closed by slips on the 22nd, while slips and debris closed the Wainuiomata Road on the 23rd.

 

To add to the misery, cold and very strong southerlies had developed over the lower North Island and northeastern South Island by the 24th. Severe southerly gales lashed Cook Strait and Wellington, with Beacon Hill averaging 70 knots, while Mt Kaukau gusted to 82 knots. Heavy seas pounded the coastline and disrupted ferry crossings. Further north, a trough crossed the north of the North Island, with thunderstorms in many areas.

 

By the 25th, the low had moved well to the east, taking the stormy weather with it.

 

Mean sea level pressure analyses for midday NZST 21st October to midday NZST 24th October in 12 hour steps are shown here.

 

 

# 7th-9th - Active trough crosses NZ, followed by wintry southerly outbreak and severe gales in northern areas.

 

A low, which had developed in the western Tasman on the 5th and 6th, moved towards central NZ on the 7th and to the east the next day. Fronts in the moist northerly flow ahead of this low brought heavy rain to exposed western areas from Westland to Taranaki, e.g. 152mm at Devil's Boot (Northwest Nelson), 108mm at Angel Knob, Tararuas, and 156mm at North Egmont. Northerly winds reached gale force about Cook Strait, with Mt Kaukau gusting to 69 knots. Onshore northeasterlies moved onto an existing cold air mass in Canterbury, resulting in a cold, wet day there with only 10C maximums in Christchurch and Ashburton. Snow fell on the inland high country, being reported briefly as low as about 700m in morning at Porters Pass.

 

The low moved away to the Chathams on the 8th, but deepened to below 980hp, leaving an unstable trough over NZ. Several fronts crossed the country, with an unseasonably cold southerly sweeping up over the South Island during the day. Snow showers fell to low levels in many parts of Otago and Southland, including Dunedin's hill suburbs. The change moved into Canterbury in the afternoon, with hail and thunder in some areas, followed by a period of more persistent rain. This chilled the atmosphere enough to allow snow to fall to unusually low levels on the plains, e.g. 5cm in Geraldine, flurries in Ashburton and even briefly at Weedons, only a short distance southwest of Christchurch. (it dropped to as low as 2C in the city during the evening)

 

On the 9th, another low formed over North Island as the cold change spread onto the island. This low deepened and then moved to the east, resulting in a very strong south to southwest flow in its wake. Severe southwesterly gales lashed northern areas, with gusts reaching 80 knots at Manukau, and 77 knots at Auckland's Sky Tower, which was closed during these winds. There was much damage, with the Fire Service responding to about 300 calls involving damage to trees, buildings etc. The squally showers accompanying these winds included hail, with a heavy hailstorm blanketing parts of Mt Maunganui in afternoon. In the eastern Bay of Plenty, a small tornado damaged trees and a house at Waiotahi, near Opotiki. Further south, snow fell on the high country (including the Desert Road), while Palmerston North recorded a wintry maximum of only 10C.

 

Mean sea level pressure analyses for midday NZST 7th October to midday NZST 9th October in 12 hour steps are shown here.

 

# 13th/14th November - Violent northwesterly storm with heavy rain and gales.

 

A low deepened to below 960hp in Sub Antarctic latitudes during the 13th, with a northwesterly flow increasing over southern and central NZ later in the day. Very heavy rain developed about and west of the Southern Alps, and continued into the 14th, when the heavy falls extended to the Nelson Ranges and the Tararuas. Totals included 203mm at Colliers, 280mm at Arthurs Pass,  Not surprisingly, there was significant flooding, with major rivers reaching their highest levels for many years. (Rakaia at its highest level in 25 years; Waimakariri its highest in 10 years) State Highway 73 was closed by the flooding.

 

Elsewhere, a period of northwesterly gales lashed many eastern areas and Cook Strait. These were especially severe about inland North Canterbury, where there is extensive damage. The actual wind direction there was north to northwest, so many locations which would've been somewhat sheltered in a straight northwesterly, were exposed to this less common direction. Severe damage resulted, and a man died after a tree fell on him while he was clearing debris from the highway between Culverden and Hanmer. While North Canterbury was worst affected, Wellington didn't escape the wrath of the winds, with trees felled on Mt Victoria and a truck overturned near the Rimutaka Road summit. If there was any consolation to this event, it was definitely warm, with a 30C maximum in Kaikoura and 29C in Hastings.

 

Mean sea level pressure analyses for midday NZST 13th October to midnight NZST 14th October in 12 hour steps are shown here.

 

NB. In the September newsletter, several events were accidentally omitted in late August. Here they are:

 

AUGUST 2006

 

# 23rd - Heavy frosts in many areas in wake of cold southerly outbreak of previous day.

 

# 24th - Several vehicles are trapped by snow on Desert Road overnight, as moist air with a cold front arrives over an existing cold air mass.

 

# 26th - Low and frontal system crosses central NZ with heavy rain causing yet more flooding and slips, including Wellington. 100mm in 15 hours at Kelburn. 80-100mm in a 9 hour period on Mt Taranaki and Tararuas. (this event was accidentally tagged onto the the notes on the events of August 21st/22nd)

 

# 28th - Westerly gales in the far south, but Southwest Cape on Stewart Island has gusts up to 166kph.

 

# 29th-31st - Warm spell in eastern areas to end a not so warm winter. 22C max in Timaru. (29th) 24C max in Kaikoura and 20-22C in many other eastern places. (31st).

 

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CHRISTCHURCH WEATHER - SPRING 2006 (Ben Tichborne)

 

 

SEPTEMBER

 

After an unsettled winter, this month was mild and very dry with west or northwest flows predominating. There were only a few days with light showers; otherwise the weather was generally sunny. Some light frosts occurred following brief cooler changes, but daytime temperatures reached above 20C on a number of occasions.

 

OCTOBER

 

After the early foretaste of summer in September, this month brought a return to unsettled conditions with a wide variety of weather. A complex low crossing northern and central NZ brought some heavy rain overnight 3rd/4th, with strong cold southerlies on the morning of the 4th. An even colder southerly brought snow down to about 450m on Banks Peninsula overnight 9th, and while it was mostly fine in Canterbury during the very cold southwesterly flow of the 10th, there were isolated reports of small hail and sleet. From the 11th-15th, a much warmer westerly flow brought generally fine weather, but there were northwesterly gales overnight on the 12th and again on the afternoon of the 13th. Another cold, showery southerly change brought some hail and thunder to the Christchurch area on the 16th, clearing by the next morning.

 

Labour Weekend was rather dull and cold with some rain and drizzle, as a low pressure system crossed to lie east of central NZ by the 24th. Showers persisted until the early hours of the 25th, as the low moved away and southerlies gradually weakened. The last spell of inclement weather for the month occurred overnight 29th/30th, as a low developed on a trough just to the east of Banks Peninsula. This resulted in a brief period of cold and severe gale southerlies, with some power outages in mid Canterbury and Banks Peninsula caused by falling trees. Heavy rain also fell for a time on the peninsula.

 

NOVEMBER

 

The topsy-turvy weather patterns of October continued into November, with more wide variability. There were several days of warm northwesterly weather, with winds reaching gale on the 14th. (severe and damaging gusts affected inland North Canterbury) By contrast, there were also a number of cold, wet spells. The 6th and 7th were cold and wet as a low moved towards the upper South Island, bringing moisture onto Canterbury while the existing air mass was cold. Snow fell on the inland high country. An even colder southerly outbreak swept over the area late afternoon of the 8th, heralded by scattered hail and thunder in mid Canterbury, followed by a period of rain. Temperatures plummeted to unseasonably cold figures, bringing snow to low levels on the plains, with flurries in Ashburton, Rolleston, and a little sleet in Christchurch. Light snow was visible on the higher Port Hills and above about 400m on Banks Peninsula by the next morning.

 

Another wet spell delivered periods of rain to the city on the 17th and 18th, while the 30th was also cold and wet, with strong southerlies and snow again on the inland high country. Thunderstorms and hail hit parts of the city and environs on the 26th and 27th, with some heavy 'pea sized' hail reported on the latter occasion.

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