Tropical Visitors produce Wild Weather

National Climate Summary January 2011

Tropical Visitors produce Wild Weather

• Rainfall: Three ex-tropical cyclones affected New Zealand during the month, bringing torrential rainfall to numerous regions. Rainfall totals were four times January normal in eastern Northland and Auckland, the Firth of Thames, Coromandel and western Bay of Plenty, and double January normal over much of the rest of the North Island. Rainfall was also above normal for Westland, Kaikoura Coast and parts of Southland and Otago. In contrast, it was rather dry for parts of inland south Canterbury and the Nelson Ranges.

• At the end of January, significant soil moisture deficits (more than 110 mm of deficit) remained in parts of Canterbury and Central Otago, but soils in the North Island were much wetter than usual for the time of year.

• Temperatures: Well above average in parts of Northland, Auckland, Waikato, Bay of Plenty, and above average across much of the remainder of the North Island, coastal Westland and Fiordland. Near average for much of the South Island, as well as Wellington, Wairarapa, Hawkes Bay.

• Sunshine: Very cloudy in Coromandel, Bay of Plenty, Gisborne, Wellington, Wairarapa, Marlborough, north Canterbury and Otago, due to easterly winds. Well above normal sunshine totals in south Canterbury, and rather sunny in Taranaki and the Ruapehu District. Near normal January sunshine totals elsewhere.

In January 2011 much lower-than-usual pressures affected the region north of New Zealand, resulting in more easterly winds than normal over the country. During the month, three lows of tropical origin brought torrential rain and gales; former tropical cyclones Vania and Zelia produced heavy rain on the 18th on the West Coast, resulting in the Fox River bursting its banks. A low of tropical origin (which formed near New Caledonia) moved towards New Zealand on January 22/23, producing extremely heavy rainfall, flooding, slips and road closures over much of the North Island, north of about Wanganui. Also, Tropical Cyclone Wilma moved rapidly across the northeastern North Island on the 28th/29th, causing widespread deluge rainfalls, severe flooding and slips, in northeastern regions of the North Island.

Rainfall totals were about four times (400 percent of) January normal in eastern Northland and Auckland, the Firth of Thames, Coromandel and western Bay of Plenty - with many new records set - and at least double (200 percent of) January normal over the rest of the North Island (the exceptions were Wellington, the Kapiti Coast and parts of the Manawatu, which recorded between 120 and 150 percent of normal). January rainfall totals were also above normal (more than 120 percent of normal) for Westland, the Kaikoura Coast and parts of Southland and Otago. In contrast, it was a rather dry month for parts of inland south Canterbury and the Nelson Ranges (which recorded less than 50 percent of normal). Elsewhere, January 2011 rainfall totals were closer to January normal (between 80 and 120 percent of normal).

At the end of January, soil moisture levels were well above normal across the entire North Island due to the extremely wet month, replacing significant soil moisture deficits that had previously affected parts of western Northland, Waikato, Bay of Plenty, Gisborne, Manawatu and Wairarapa. Significant soil moisture deficits (more than 110 mm of deficit) remain, however, in parts of Canterbury and Central Otago.

Mean monthly temperatures for January 2011 were well above average (at least 1.2 °C above average) in parts of Northland, Auckland, Waikato, and Bay of Plenty, and above average (between 0.5 °C and 1.2 °C above average) across much of the remainder of the North Island, as well as for coastal Westland and Fiordland. Temperatures were near average (within 0.5 °C of average) over much of the South Island, as well as in Wellington, Wairarapa and Hawkes Bay. The New Zealand national average temperature was 17.4°C (0.3°C above the 1971–2000 January average).

Sunshine totals in Coromandel, Bay of Plenty, Gisborne, Wellington, Wairarapa and Marlborough were below normal (between 75 and 90 percent of January normal), showing the effect of the prevailing easterly winds during the month. In contrast, it was very sunny in south Canterbury with well above normal sunshine totals (more than 125 percent). Sunshine totals in Taranaki and the Ruapehu District were also above normal (between 110 and 125 percent of normal). Elsewhere, January sunshine totals were near normal.

Further Highlights: • The highest temperature was 35.8°C, recorded at Timaru on the 16th.

• The lowest temperature was -0.1°C, recorded at Masterton on the 14th.

• The highest 1-day rainfall was 276 mm recorded in the Firth of Thames on the 28th.

• The highest wind gust was 165 km/hr, recorded at Cape Turnagain on the 16th.

• Of the six main centres in January 2011, Tauranga was the wettest but also the sunniest, Christchurch the driest, Auckland the warmest and Dunedin the coolest. For all of the six main centres except Dunedin, it was a wetter-than-usual January.

ENDS

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