National Climate Summary - July 1999

MONDAY 2 AUGUST 1999

NATIONAL CLIMATE SUMMARY - JULY 1999

VERY WET IN THE EAST OF THE SOUTH ISLAND
ANOTHER MILD MONTH
A MONTH OF EXTREMES

July was much wetter than normal over much of the South Island, especially in the east from Marlborough to Otago. Canterbury and Banks Peninsula locations recorded more than twice their normal rainfall. This has now recharged soil moisture levels in the previous drought-affected areas in Canterbury and Otago. Drier than normal conditions occurred in Neslon, Buller and the east of the North Island.

It was yet another mild month with the national average temperature for July of 8.4ºC being 0.7ºC above average. This was the 12th consecutive month with above normal temperatures. Near record July warmth occurred in the south west of the North Island, where mean temperatures were 1 to 1.5oC above normal, while temperatures were close to 1.0oC above normal in many other districts. The mild conditions were surprising in view of the more frequent southerly quarter winds than usual and colder conditions during the last week of the month. Less sunshine than normal occurred in Canterbury and Westland, whilst it was sunnier than usual in Northland, Wellington and Invercargill.

It was a month of extreme climate, with damaging nor'westers, and heavy snowfalls in the south at the beginning of the month. Flood producing rainfall occurred in Canterbury mid month. Winter temperatures arrived with cold southerlies in the last week. These produced snow to low levels in the south and east of the South Island, with the Ruapehu region receiving its first significant snowfall this winter.

These patterns were caused by a combination of much warmer than normal seas around New Zealand, and more lows near the Chatham Islands. These produced more southerly quarter winds than normal over much of the country.

WET OVER MUCH OF THE SOUTH ISLAND, ESPECIALLY IN THE EAST

July rainfall was well above average throughout much of Canterbury, with some locations recording more than double their normal rainfall. These were caused by more frequent rain producing events during the month, especially on the 17th and 18th. Le Bons Bay measured rainfall-totalling 292 mm for the month. All eastern areas between Marlborough and Otago received at least one and a half times the normal rainfall. It was also wetter than normal in south Westland, Fiordland, and much of Southland, with totals at least 125 percent of normal.

Very high July rainfall was measured at:

Location----|-----Rainfall----|-----total (mm)----|-----Percentage of normal ----|-----Year records began----|-----Comments

Christchurch Airport----|-----162----|-----237%----|-----1944 ----|-----3rd highest

LOWER RAINFALL IN THE EAST OF THE NORTH ISLAND, NELSON AND BULLER

Rainfall was less than 60 percent of normal in Nelson, and about 75 percent of normal in Gisborne, Hawke's Bay, Horowhenua, inland Wairarapa, and much of Buller.

MILD OVERALL, ESPECIALLY IN THE SOUTHWEST OF THE NORTH ISLAND

The Chatham Islands experienced their warmest July on record. Near record July warmth occurred in Horowhenua and Wellington, with mean temperatures 1 to 1.5oC above normal. Temperatures were also 1 to 1.5oC above normal in Wanganui and parts of Buller and Westland, and 0.5 to 1.0oC above normal in many other regions. However, temperatures were closer to normal in parts of north Canterbury and Central Otago. Near, or record high mean July temperatures were recorded at:

Location----|-----July temperature (°C)----|-----Departure from normal (°C)----|-----Year records began----|-----Comments

Levin----|-----9.6----|-----+1.2----|-----1895----|-----2nd highest
Paraparaumu Airport----|-----10.0----|-----+1.6----|-----1949----|-----2nd highest
Wellington, Kelburn----|-----9.8----|-----+1.3----|-----1863----|-----2nd highest
Wellington Airport----|-----10.5----|-----+1.3----|-----1196----|-----2nd highest

Chatham Islands----|-----9.6----|-----+1.6----|-----1878----|-----Highest

CLOUDY IN CANTERBURY AND WESTLAND

July sunshine and solar radiation totals indicated below normal values in Canterbury, and Westland. However, it was sunnier than normal in Northland, Wellington and Invercargill. Other regions experienced near average sunshine hours.

HIGHLIGHTS

Extreme temperatures

o----|-----The lowest temperature for July was -8.9oC recorded at Lauder during the morning of the 6th.
o----|-----The highest temperature for the month was 21.7.oC recorded at Dargaville on the 17th.

Violent winds followed by heavy snowfall

o----|-----Severe damaging nor'westers in Southland and Otago occurred during the morning of the 2nd, followed by one of the heaviest known snowfalls on record in the western Otago/Southern Lakes region. Wind gusts to 150 km/h were reported in the Tuatapere and Middlemarch areas, with significant property damage, dangerous blowing iron, and broken trees. Gusts to 133 km/h were recorded at Lauder (near Alexandra). More than a metre of snow was measured at Coronet Peak, with depths to 40 cm reported in low-lying rural areas. A large number of residents, especially in Glenorchy, Hawea and Gibbston were without power throughout the weekend.

High rainfall

o----|-----Significant rainfall occurred throughout Canterbury, and Banks Peninsula on the 17th, with rainfall totalling 122 mm at Le Bons Bay in the 24 hours to 9am on the 18th, and 51 mm in Christchurch City during the same period. In Christchurch the Avon River overflowed in some areas, with surface flooding almost forcing a few residents out of their homes.

Spectacular thunderstorm

o----|-----Auckland's Sky Tower was struck by 16 lightning strikes in half an hour during a violent thunderstorm on the 21st.

Further widespread snowfall

o----|-----Cold southerlies spread north from the 26th, bringing snow to low levels in the south and east of the South Island (including Christchurch), and showers of sleet and hail (with some isolated heavy falls) to the south of the North Island. The Ruapehu area received its first significant snow of the winter, with the Desert Road closed from the 26th through 29th. Snow also settled on the Rimutaka Hill road north of Wellington.

ENDS

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