January 2002

Friday, 1 February 2002

Many thunderstorms and high-rainfall / flood-producing events

• Extremely wet in Canterbury and the east, low rainfall in southern New Zealand
• Warm on the West Coast, cool in Central Otago
• Sunny in Taranaki and the west and south of the South Island
• Low sunshine in Canterbury and coastal Otago

Thunderstorms with lightning, frequently accompanied by torrential rain that resulted in localised flooding, were a feature of the January climate. There was a thunderstorm somewhere in New Zealand on twenty-two days during the month, including all but two days of the first three weeks. Many districts received twice their normal rainfall, especially in the east, while Fiordland, southern and western Southland and Northland were much drier than usual.

Rainfall in some Canterbury locations exceeded previous records. Christchurch Gardens recorded its highest January rainfall in more than 135 years of measurement. In contrast, rainfall in Fiordland, southern and western Southland was 50 percent or less than normal. Low rainfall over the past two months has resulted in significant soil moisture deficits in parts of inland Southland. As a result January soil moisture levels are lower than normal in the south of the South Island, but have reached field capacity in many normally at-risk eastern rural areas.

Mean temperatures were at least 1.0°C above normal on the West Coast, but 1.0°C below average in Central Otago. The national average temperature of 17.1°C was close to the mean January temperature for the period 1961–1990 of 17.0°C.

Taranaki, the South Island West Coast and Southland experienced more sunshine than average. However, very much lower than normal sunshine hours occurred in Canterbury and coastal Otago.

January’s climate pattern was dominated by more anticyclones (‘highs’) with well above average pressures to the far south of New Zealand, and more depressions (‘lows’) than usual in the north Tasman Sea and over the North Island extending to the east. These features resulted in more frequent easterly winds, especially over the South Island.

Wet in many areas, especially in Canterbury and the east Low rainfall in the far south

Rainfall was at least 200 percent (double) of normal in many eastern regions from Hawke’s Bay to Canterbury, including western Bay of Plenty and parts of Wellington, and more than 400 percent (four times) of normal along the Kaikoura Coast. Rainfall of at least 1.0 mm was recorded on 16 days in some Canterbury locations, as much as nine more than average. Above average rainfall, with at least 120 percent of normal occurred in eastern Bay of Plenty, Taupo, the Central North Island Volcanic Plateau, Gisborne, Wairarapa, Wanganui, Westland, Nelson, Marlborough, the Southern Alps, Otago, and eastern Southland. Other more isolated areas of above average rainfall occurred in Auckland, Waikato, King Country, and Taranaki. Northland’s rainfall was less than 75 percent of normal.

Near or record high January rainfall was recorded at:

Location	January rainfall (mm)	Percentage of normal	Year records began	Comments
Hanmer Forest	222	295	1905	2nd equal highest
Kaikoura	234	446	1950	Highest
Rangiora	174	319	1918	3rd highest
Christchurch Airport	138	297	1944	2nd highest
Christchurch Gardens	143	314	1864	Highest
Lincoln	125	235	1881	Very high
Darfield	180	279	1920	2nd equal highest
Winchmore	153	263	1947	Highest
Timaru Airport	130	239	1957	Highest
Twizel	128	256	1973	Highest
Oamaru Airport	120	303	1941	2nd highest
Chatham Islands	169	322	1951	Highest

Near record low January rainfall was recorded at:

Location	January rainfall (mm)	Percentage of normal	Year records began	Comments
Tiwai Point	36	30	1971	2nd equal lowest

Warmer on the West Coast of the South Island Cooler in Central Otago

Mean temperatures were at least 1.0°C above normal on the West Coast, and at least 0.5°C above normal in parts of Southland. However, they were about 1.0°C below average in Central Otago, and at least 0.5°C below average in Bay of Plenty, King Country, Canterbury and parts of Northland, Auckland and Hawke’s Bay. Mean temperatures were near average elsewhere.

Near or record high mean January temperatures were recorded at:

Location	Mean temperature (°C)	Departure (°C)	Year records began	Comments
Raoul Island	23.5	+1.5	1941	2nd highest

Mean daily maximum temperatures were well below average (by as much as 2.5°C) in Canterbury and Central Otago.

Sunny in Taranaki and the south and west of the South Island Rather cloudy in Canterbury and coastal Otago

Sunshine and solar radiation totals were more than 110 percent of average in Taranaki, Southland, and on the West Coast of the South Island. Much lower than normal sunshine hours were recorded in Wellington and the east of the South Island, especially in Canterbury and coastal Otago.

Near or record January sunshine hours were recorded at:

Location	January sunshine hours	Percentage of normal	Year records began	Comments
New Plymouth Airport	311	126	1973	Highest
Christchurch Airport	169	72	1949	Very low

Record low January solar radiation was recorded at:

Location	January solar radiation (MJ m-2 / day)	Percentage of average	Year records began	Comments
Kaikoura	18.3	78	1969	Lowest
Winchmore	17.0	76	1984	Lowest
Timaru Airport	15.8	72	1984	Lowest
Dunedin Airport	16.0	80	1970	Lowest

Highlights

Extreme temperatures

• The highest air temperature for the month was 34.4°C, recorded at Timaru Airport, on the 2nd. The highest January air temperature on record at Timaru Airport is 34.9°C.
• The lowest air temperature for the month was –0.5°C, recorded at Waiouru, on the 7th. The lowest January air temperature on record at Waiouru is –2.7°C.
• Air temperatures reached all-time records with 7.5°C at Scott Base in the Antarctic on the 11th and 7.0°C on the 12th. The previous record was 6.5°C in both December 1984 and January 1960. Measurements began in 1957.

Tornado

• A tornado passed over the Levin golf course just before 4pm on the 4th, leaving a number of trees uprooted.

Lightning strikes

• A tourist was struck by lightning twice while tramping on the Ben Lomond track near Queenstown about 3pm on the 4th.
• Hokitika Airport recorded 481 lightning flashes on 2nd January, and 937 flashes for the first four days of the month.

Hailstorm

• Thunderstorms, lightning, torrential rainfall and hail occurred over Christchurch during the afternoon the 5th, with hail lying up to 7.5 cm deep in some city areas.

Significant rainfall events and flooding

• Heavy rainfall (as much as 38 mm in an hour) deluged Westport on the 3rd with some flood damage reported. High rainfall (64 mm) also occurred in Balclutha on the same day.
• Thunderstorms over Wellington City on the 10th resulted in torrential rainfall (about 40 mm in 30 minutes, and 52 mm in an hour) and flash floods in the city center just after 7pm. This rainfall event had an average recurrence interval of well over 100 years. Thunderstorms, some with hail, and surface flooding also occurred over Wanganui, Manawatu, the central and eastern North Island, Buller and Nelson. Rainfall at Napier Airport totaled 29 mm in the hour to 9pm on the 10th. Hastings rainfall totaled 77 mm for the 24 hours to 9am on the 11th.
• Houses were flooded and evacuated in Akaroa, the Kowhai Bridge washed out, and the water supply cut after heavy rainfall over the 12th–13th. The same weather system produced high rainfall, slips and surface flooding throughout Canterbury and the Kaikoura Coast (109 mm at Hanmer Forest, 106 mm at Kaikoura, 100 mm at Snowden for the 24 hours to 9am on the 13th). SH1 was closed due to flooding in several places, with the Orari Bridge washed out south of Oamaru. High rainfall and flooding also occurred near Thames in the North Island, where the Tararu Stream overflowed its banks forcing 25 homes to be evacuated.
• Further high rainfall (as much as 70mm) occurred in parts of northern and inland Canterbury on January 18th.

For further information, please contact:

Dr Jim Salinger – Principal Scientist, Climate NIWA National Climate Centre – Auckland Phone +64 9 375 2053 [email protected]

Stuart Burgess – Climatologist NIWA National Climate Centre – Wellington Phone +64 4 386 0569 [email protected]

Geoff Baird – Communications Manager Phone +64 4 386 0543 [email protected]

Acknowledgement of NIWA as the source is required.