WEATHER
Rainfall
Spring westerlies produced a very wet month in western regions of the South Island, as well as for Nelson, Southland, and parts of Central Otago. In contrast, it was a dry September in eastern areas of both Islands.
Temperature
A mild September for the lower South Island, as well as north Canterbury, Coromandel, the Hauraki Plains, and the Rodney District. Elsewhere, temperatures were close to September average.
Sunshine
An extremely sunny September for eastern parts of both Islands. Rather cloudy for Westland. Generally close to average sunshine elsewhere.
Soil moisture
At the end of September, soil moisture levels were slightly drier than usual for Taranaki, Waikato, Central Plateau, and parts of the Bay of Plenty, Gisborne, Hawkes Bay, and coastal Wairarapa. Soil moisture levels in Dunedin and across south Canterbury remain above normal.
Overview
Spring westerlies arrived during the first few days of September, and prevailed during the first half of the month. These stormy westerly quarter winds produced very wet conditions on the West Coast of the South Island, but in contrast, a rather dry month in eastern areas of both islands. From mid-month, a pattern change saw more anticyclones than usual lie over New Zealand and to the east of the country. This combination of patterns resulted in more northwest winds than normal over New Zealand for the month of September, overall.
The frequent west to northwest winds of September produced a very wet September for western regions of the South Island, as well as for Nelson, much of Southland, and Central Otago, with totals exceeding one and a half times September normal rainfall in these regions. Above normal rainfall was also observed in eastern parts of Northland. In contrast, it was a rather dry September in eastern areas of both Islands, illustrating the lee effect of westerly winds. In particular, rainfall was less than half of September normal for parts of Gisborne, Hawkes Bay and Canterbury. Below normal rainfall was also experienced between Wanganui and Wellington. Across the remainder of the country, rainfall was generally near normal.
At the end of September, soils were slightly drier than is usual for the time of year for Taranaki, Waikato, Central Plateau, and parts of the Bay of Plenty, Gisborne, Hawkes Bay, and coastal Wairarapa. Soil moisture levels in Dunedin and across south Canterbury remain above normal for the time of year. Elsewhere, soil moisture levels were generally close to normal.
It was a mild September over the lower South Island, as well as for north Canterbury, Coromandel, the Hauraki Plains, and the Rodney District, with temperatures between 0.5°C and 1.2°C above the September average. Elsewhere, temperatures were generally near average. The nation-wide average temperature in September 2012 was 10.8°C (0.4°C above the 1971-2000 September average), using NIWA’s seven-station temperature series which begins in 1909. Notably, an unusually cold southerly air stream for the time of year affected New Zealand between 11 and 13 September, with record or near-record low September temperatures observed at many locations. In stark contrast, the last two days of September were extremely warm.
It was an extremely sunny September for eastern areas of both Islands (with sunshine totals typically exceeding 125 percent of September normal), reflecting the high frequency of westerly winds during the month. In contrast, it was a rather dull September for Westland. Elsewhere, sunshine totals were generally close to normal.
Further Highlights:
The highest temperature was 25.5°C, observed at Waiau on 30 September.
The lowest temperature was -8.1°C, recorded at Mt. Ruapehu on 13 September.
The highest 1-day rainfall experienced was 165 mm at Milford Sound on 14 September.
The highest gust recorded was 169 km/hr at Southwest Cape, Stewart Island, on 6 September.
Of the six main centres in September 2012, Christchurch was the driest but also the coolest; Wellington was the sunniest, Hamilton the cloudiest, Tauranga the warmest, and Auckland the wettest.
Rainfall: A very wet September for western regions of the South Island, as well as for Nelson, Southland and Central Otago. In contrast, a dry September for eastern areas of both Islands.
The frequent west to northwest winds of September produced a very wet September for western regions of the South Island, as well as for Nelson, much of Southland, and Central Otago, with totals exceeding one and a half times (150 percent of) September normal rainfall in these regions. Above normal rainfall was also observed in parts of Northland (with totals between 120 and 149 percent of September normal). In contrast, it was a rather dry September in eastern areas of both Islands, illustrating the lee effect of westerly winds. In particular, rainfall was well below normal (less than 50 percent of September normal) for parts of Gisborne, Hawkes Bay and Canterbury. Below normal rainfall (between 50 and 79 percent of September normal) was also experienced between Wanganui and Wellington. Across the remainder of the country, rainfall was generally near normal (between 80 and 119 percent of September normal).
Record or near-record September rainfall totals were recorded at:
Location
Rainfall total (mm)
Percentage of normal
Year records began
Comments
Record high or near-record high
Nelson
151
177
1941
4th-highest
Appleby
163
185
1941
Equal 3rd-highest
Manapouri
202
190
1961
Equal 4th-highest
Lumsden
94
142
1982
3rd-highest
Record low or near-record low
Wairoa
19
21
1964
2nd-lowest
Mahia
19
29
1990
3rd-lowest
At the end of September, soils were slightly drier than is usual for the time of year for Taranaki, Waikato, Central Plateau, and parts of: the Bay of Plenty, Gisborne, Hawkes Bay, and coastal Wairarapa. Soil moisture levels in Dunedin and across south Canterbury remain above normal for the time of year. Elsewhere, soil moisture levels were generally close to normal.
Temperature: A mild September over the lower South Island, as well as for north Canterbury, Coromandel, the Hauraki Plains, and Rodney.
It was an unusually mild September over the lower South Island, as well as for north Canterbury, Coromandel, the Hauraki Plains, and the Rodney District, with temperatures between 0.5°C and 1.2°C above the September average. Elsewhere, temperatures were generally near average (within 0.5°C of the September average).
The nation-wide average temperature in September 2012 was 10.8°C (0.4°C above the 1971-2000 September average), using NIWA’s seven-station temperature series which begins in 19091.
Record2 or near-record mean minimum air temperatures for September were recorded at:
Location
Minimum
air temp. (oC)
Departure from normal3(oC)
Year records began
Comments
Record high or near-record high
Alexandra
3.7
1.3
1983
4th-highest
Gore
5.2
1.2
1971
4th-highest
Record or near-record mean maximum air temperatures for September were recorded at:
Location
Maximum
air temp. (oC)
Departure from normal (oC)
Year records began
Comments
Record high or near-record high
Leigh
18.2
1.8
1966
Highest
Motueka
17.4
1.7
1956
3rd-highest
Cheviot
15.8
0.7
1982
3rd-highest
Ranfurly
14.6
1.5
1975
4th-highest
Sunshine: An extremely sunny September for eastern parts of both Islands. Rather cloudy for Westland. Generally close to average sunshine elsewhere.
It was an extremely sunny September for eastern areas of both Islands (with totals typically exceeding 125 percent of September normal), reflecting the high frequency of westerly winds during the month. In contrast, it was a rather dull September for Westland, with sunshine totals around 80 percent of September normal. Elsewhere, sunshine totals were generally close to normal.
Record or near-record September sunshine hours were recorded at:
Location
Sunshine hours
Percentage of normal
Year records began
Comments
Record high or near-record high
Gisborne
241
133
1905
2nd-highest
Waipawa
210
149
1945
4th-highest
Cheviot
199
138
1983
3rd-highest
Balclutha
174
127
1964
4th-highest
September climate in the six main centres
Of the six main centres, Christchurch was the driest but also the coolest; Wellington was the sunniest, Hamilton the cloudiest, Tauranga the warmest, and Auckland the wettest.
September 2012 main centre climate statistics:
Temperature
Location
Mean temp. (oC)
Departure from normal (oC)
Comments
Aucklanda
12.6
-0.4
Near average
Taurangab
12.8
+0.4
Near average
Hamiltonc
11.4
+0.1
Near average
Wellingtond
11.2
+0.4
Near average
Christchurche
9.7
+0.3
Near average
Dunedinf
10.5
+1.0
Above average
Rainfall
Location
Rainfall (mm)
% of normal
Comments
Aucklanda
92
89%
Near normal
Taurangab
68
81%
Near normal
Hamiltonc
90
89%
Near normal
Wellingtond
64
66%
Below normal
Christchurche
32
79%
Below normal
Dunedinf
53
109%
Near normal
Sunshine
Location
Sunshine (hours)
% of normal
Comments
Aucklanda
164
109%
Near normal
Taurangab
170
98%
Near normal
Hamiltong
144
99%
Near normal
Wellingtond
189
116%
Above normal
Christchurche
184
108%
Near normal
Dunedinf
168
125%
Well above normal
a Mangere b Tauranga Airport c Hamilton Airport d Kelburn e Christchurch Airport f Musselburgh g Ruakura
Highlights and extreme events
Rain and slips
The highest 1-day rainfall experienced in September was 165 mm, observed at Milford Sound on 14 September.
On 3 September, heavy rain caused flooding and property damage in Auckland and Northland. The northbound Esmonde Road onramp to SH1 was flooded, some schools were closed, and flights were delayed.
A slip closed SH6 at the Haast Pass between Haast and Hawea on 6 September.
On 8 September, torrential rain caused a slip, which closed one lane of SH1 south of Paekakariki for about two hours. Parts of Manawatu also suffered surface flooding.
State Highway 1 was closed by a slip at Hihitahi, between Taihape and Waiouru, on 10 September.
On 13 September, after recent heavy rain and snow, a large section of Skippers Canyon Road at Devil’s Elbow slipped into the Shotover River, closing the road.
On 16 September, another slip closed SH6 at Makarora. Overnight closures were planned to clear the slip. In the Bay of Plenty, heavy rain caused slips and turned paddocks into lakes.
On 17 September, very heavy rain in Wellington caused surface flooding, affecting commuter traffic. All buses were running 15 minutes late. Slips in Wadestown closed the Johnsonville railway line, and Mairangi Road, with other roads affected by slips. There were reports of heavy water flows blowing off manhole covers.
On 19 September, a large slip came down on SH35 at the new alignment on Maraenui Hill.
Record or near record September extreme 1-day rainfall totals were recorded at:
Location
Extreme 1-day rainfall
(mm)
Date of extreme rainfall
Year records began
Comments
Ranfurly
24
26th
1943
4th-highest
Manapouri
60
14th
1963
2nd-highest
Lumsden
26
14th
1982
3rd-highest
Temperatures
The highest temperature recorded in September was 25.5°C, observed at Waiau on 30 September. The lowest temperature was -8.1°C, recorded at Mt. Ruapehu on 13 September.
An unusually cold southerly air stream for the time of year affected New Zealand on 11 and 12 September, breaking September records at many southeastern sites. Afternoon temperatures on the 12th at Martinborough and Mahia were the coldest on record for September (see Tables next two pages). On the following morning (13 September), ridging produced clear skies and light winds, which resulted in record or near-record low minimum temperatures at numerous locations across the country. It was a record cold September morning on the 13th at Kerikeri, Warkworth, Whangaparaoa, Rotorua and Te Kuiti. Also notable was the -4.4°C minimum temperature recorded at Christchurch Airport on the 13th, being equal to the second-lowest September temperature in a group of Christchurch stations which date back to 1863.
In stark contrast, the last two days of September were extremely warm, with many sites experiencing near-record September warmth. Cheviot observed 25.1°C on 30 September, a new September record there since records began in 1982, and Dunedin Airport recorded 24.9°C on the same afternoon (equalling the September record there).
Record or near-record daily minimum air temperatures for September were recorded at:
Location
Extreme minimum (°C)
Date of extreme temperature
Year records began
July ranking
High records or near-records
Paraparaumu
14.0
8th
1972
Equal 2nd-highest
Wellington (Airport)
14.2
8th
1972
2nd-highest
Wanganui
14.3
8th
1972
Equal 4th-highest
Hokitika
12.9
7th
1866
3rd-highest
Greymouth
12.9
7th
1972
Highest
Cheviot
12.7
6th
1982
2nd-highest
Oamaru
13.3
6th
1908
Equal 4th-highest
Ranfurly
10.9
6th
1975
2nd-highest
Alexandra
12.9
6th
1983
Highest
Low records or near-records
Kaitaia
2.0
13th
1967
3rd-lowest
Kerikeri
0.9
13th
1981
Lowest
Leigh
4.8
13th
1966
Equal 3rd-lowest
Warkworth
-0.5
13th
1966
Lowest
Whangaparaoa
4.6
12th
1982
Lowest
Whakatane
-1.0
13th
1975
Equal 4th-lowest
Rotorua
-3.2
13th
1964
Lowest
Taupo
-4.7
13th
1949
4th-lowest
Hamilton
-3.5
13th
1906
2nd-lowest
Port Taharoa
2.0
13th
1973
Equal 3rd-lowest
Te Kuiti
-2.4
13th
1959
Lowest
New Plymouth
-1.3
13th
1944
2nd-lowest
Castlepoint
1.2
12th
1972
3rd-lowest
Hicks Bay
2.3
13th
1969
Equal 3rd-lowest
Hokitika
-1.9
12th
1963
3rd-lowest
Haast
-1.5
12th
1949
Equal 3rd-lowest
Motueka
-2.4
12th
1956
2nd-lowest
Cheviot
-2.9
13th
1982
4th-lowest
Christchurch (Airport)
-4.4
13th
1863
Equal 2nd-lowest
Le Bons Bay
0.2
12th
1984
2nd-lowest
Ranfurly
-5.9
13th
1975
Equal 4th-lowest
Record or near-record daily maximum air temperatures for September were recorded at:
Location
Extreme maximum (°C)
Date of extreme temperature
Year records began
July ranking
High records or near-records
Kaikohe
21.3
29th
1973
3rd-highest
Leigh
22.8
30th
1966
2nd-highest
Hamilton
22.5
29th
1906
2nd-highest
Te Kuiti
22.1
29th
1959
Equal 3rd-highest
Ngawi
21.6
30th
1972
4th-highest
Wairoa
25.3
30th
1964
4th-highest
Reefton
22.2
29th
1960
3rd-highest
Milford Sound
18.6
29th
1934
Equal 4th-highest
Motueka
23.1
7th
1956
4th-highest
Blenheim
24.6
30th
1941
2nd-highest
Cheviot
25.1
30th
1982
Highest
Ranfurly
21.7
29th
1975
3rd-highest
Dunedin (Airport)
24.9
29th
1962
Equal highest
Manapouri
20.3
29th
1963
3rd-highest
Lumsden
22.7
29th
1982
2nd-highest
Tiwai Point
21.8
29th
1970
3rd-highest
Balclutha
22.7
25th
1964
4th-highest
Low records or near-records
Dargaville
12.0
12th
1951
4th-lowest
Whangaparaoa ws
11.7
12th
1982
2nd-lowest
Castlepoint
7.9
12th
1972
2nd-lowest
Martinborough
8.5
12th
1986
Lowest
Gisborne
9.0
12th
1940
2nd-lowest
Mahia
8.5
12th
1990
Lowest
Wanganui
9.9
12th
1987
2nd-lowest
Reefton
7.1
11th
1972
2nd-lowest
Ranfurly
4.2
11th
1975
3rd-lowest
Dunedin (Airport)
6.1
11th
1972
3rd-lowest
Dunedin (Musselburgh)
6.1
11th
1947
4th-lowest
Manapouri
4.6
11th
1973
4th-lowest
Queenstown
3.2
11th
1871
2nd-lowest
Lumsden
4.4
11th
1982
3rd-lowest
Wind
The highest wind gust recorded in September was 169 km/hr, at Southwest Cape on 6 September.
On 3 September, strong winds brought down trees in the Bay of Plenty, closing some secondary roads. In Tauranga city, a strong gust blew the head off a Queen Palm tree leaving just a tall stump. On 4 September, a wind warning was issued for SH87 between Outram and Middlemarch.
On 5 September, wind warnings were issued for SH1 between Waikouaiti and Milton, SH8 between Fairlie and Twizel, and SH80 between Pukaki and Mr Cook. In the Mackenzie Country, the wind closed Mt Dobson ski field, with snow drifts blown on to the access roads. At the Remarkables, the Freeski Open of New Zealand final was delayed after strong winds closed the ski field.
On 6 September, strong winds brought down power lines in Balclutha, and uprooted trees at Whataroa on the West Coast. Wind warnings were issued for SH73 at Porters Pass. The Lux-Mini Light Festival on the Wellington waterfront was closed early because of the strong winds.
On 7 September, strong winds battered Wellington, bringing down power lines and trees, cutting power to some northern suburbs.
On 8 September, strong winds closed SH2 over the Rimutaka Ranges. Flights at Wellington Airport were cancelled, delayed or diverted. Power poles, telephone lines and trees were brought down, tramplines were sent flying, roofs were lifted, and in the central city, the wind forced a window at the Amora Hotel to crash onto Wakefield Street, and a large sign on Dixon Street was uplifted, smashing into a car, breaking its windscreen. Gusts caused powerlines to clash, resulting in about 6000 homes in Upper Hutt, and another 700 in Wainuiomata, losing power for several hours. In Taranaki, high winds brought down trees and cut power to 1600 homes. A Stratford supermarket had to close for more than an hour when glass panels on the entrance roof were lifted by the wind. Trees were also brought down in Manawatu, while in Wairarapa, power lines were downed and roofs lifted. Wind warnings were issued for SH1 between Blenheim and Kaikoura.
On 10 September, wind warnings were issued for SH1 between Allanton and Gore, SH8 between Clarksville and Raes Junction, SH73 at Porters Pass, SH87 between Outram and Kyeburn, and SH90 between Raes Junction and Gore. In Invercargill, trampolines were sent flying and trees toppled, and power cuts were reported in Winton, Otatara and Invercargill. In central Tauranga, a large waka sail on a stainless steel pole, blew over in strong winds blocking the railway line.
On 11 September, wind warnings were issued for SH1 between Balclutha and Gore. In the Hutt Valley, a roof was blown off a home, cutting power to neighbouring houses.
On 14 September, wind warnings were issued for SH8 between Fairlie and Twizel, SH73 at Porters Pass, and SH80 between Pukaki and Mt Cook Village.
On 17 September, strong winds in Christchurch uprooted a large tree growing on the Avon River bank. In Queenstown, the wind disrupted flights, with some planes diverted to Dunedin, or returned to Christchurch.
Record or near record September extreme wind gusts were recorded at:
Location
Extremewind gust (km/hr)
Date of extremegust
Year records began
Comments
Tauranga
98
9th
1973
3rd-highest
Taupo
80
8th
1982
4th-highest
Baring Head
143
8th
1991
Equal 3rd-highest
Wellington (Airport)
128
8th
1972
Equal 4th-highest
Kaikoura
122
17th
1972
Equal 3rd-highest
Oamaru
80
4th
1984
4th-highest
Lightning and hail
On 4 September, Christchurch had thunder, lightning and a severe hailstorm in the early evening. Conservatories and cars were damaged, power was lost to some suburbs, and one flight was delayed. Thunderstorms were also reported in Buller, Northland, Wellington and the Waikato.
On 8 September, a lightning storm in Manawatu caused a brief power outage in Wellington City. It occurred at half time in the rugby match between New Zealand and Argentina, causing a 30 minute delay as the lights had to cool down before being restarted. Hail storms also passed through Manawatu.
On 9 September, Hamilton and the surrounding region experienced thunder, lightning, and torrential downpours of hail, damaging cars.
On 11 September, hail fell in Wellington and Palmerston North.
On 17 September a fast-moving front brought thunderstorms to mid-Canterbury.
Snow and ice
On 5 September, SH94 was closed between Te Anau and Milford Sound because of the danger of avalanche caused by snow melt. It remained closed on 6 and 7 September.
On 9 September, snow fell on SH73 between Arthurs Pass and Otira, closing the road to towing vehicles, with chains required on all other vehicles.
On 10 September, heavy snow closed SH94 between Te Anau and Milford Sound. Chains were required on SH73 between Arthurs Pass and Otira, and the road was closed to towing vehicles.
On 11 September, SH94 remained closed by snow, Chains were essential on SH7 at the Lewis Pass, SH6 between Athol and Lumsden, SH94 between Mossburn and Te Anau, and the Crown Range Road between Arrowtown and Wanaka. These roads were closed to towing vehicles. Snow also affected SH1 between Balclutha and Gore, SH93 between Clinton and Mataura, SH6 between Kingston and Arrow Junction, and SH6A between Frankton and Queenstown, where chains had to be carried. The snow closed Queenstown Airport with about 30 flights diverted. Garston School was closed for the day, with 13 cm of snow measured at the school. In Dunedin, snow in the hill suburbs delayed starting times for schools and kindergartens with some high roads closed, and later in the day traffic in the hill suburbs came to a halt when hail stones froze on roads in the late afternoon. Taxis stopped running to the hill suburbs about 7 pm, and bus services were affected by sleet, snow and hail all day. SH1 was closed between Rangipo and Waiouru in the late afternoon.
On 12 September, snow closed SH2 over the Rimutaka Ranges from early morning. Extreme care was required on SH25, the Napier-Taupo road. Furter south, SH87 between Outram and Middlemarch and SH94 from Te Anau to Milford Sound were closed, and chains were required on SH73 at Porters Pass. Residents on Wellington’s hill suburbs reported snow falling but not settling. Snow was also reported around Palmerston North and in Norsewood.
On 14 September, SH94 remained closed by snow at the Lower Hollyford turn-off to Milford Sound.
Cloud and fog
On 17 September, fog caused delays at Christchurch Airport.
On 28 September, fog caused flight cancellations at Gisborne Airport.
On 29 and 30 September, fog rolled across Hawkes Bay, causing cancellations and delays at Napier Airport.
(Source)