The coming summer will start late and finish late. The first summer month, December, may be wetter than average for many North Island regions, but drier than average across most of the South Island. Much rain comes in the second week of the month and then there are wet conditions around Christmas, which may affect camping and outdoor festivals. With king tides right on Christmas, there may be some flooding particularly in the top half of the North Island. It may be advisable to secure boats until the weather eases after Boxing Day. However the South Island may only receive light Christmas showers. The sunniest spell in December, good for haymaking across the country, may be between 15th-22nd.
January is wetter than average for the North island but slightly drier than average for the South Island. December and January have useful dry spells punctuated by short periods of heavy downpours. January is wet mainly in the second and fourth weeks, bringing hay-making opportunities in the first and third weeks for both islands. February should be dry and sunny, particularly for the whole first half of the month which will be mostly rain-free for most of the country. Most February rain arrives between 14-22 February. March is much wetter than the long term average for the North Island, but may overall bring below average rain for the South Island.
December is sunnier than average for the South Island but sunshine hours may be just below the average for the North Island. January and February deliver roughly getting similar sunshine trends. March is sunnier than average for the South Island but cloudier for the North island. Overall it indicates a sunnier summer for the South as compared to the North islands. December's temperatures are below average for both islands, also below the average for January and February across the North Island. Whilst the South Island may have temperatures close to average for January, in February the South Island may be a warmer than average.
Unusually high tides will be a feature of the first four months of 2015. They will occur during 21-24 January, 19-22 February, 20-23 March and 17-20 April, and will feed cyclonic developments to the north of NZ. Cyclonic remnants in the second week of January may bring high winds to Northland, Coromandel and BoP. Another system coming through New Caledonia may bring rain to the North Island and Canterbury. In January’s fourth week a further system passing through the Kermadecs will bring rain across NZ In February's third week a cyclone through Fiji and Tonga will bring rain to the North Island around 14-18, persisting to the 21st for some districts, and will affect the South Island around 14-16 and 20-21.
In the first week of March a cyclone passing through Vanuatu brings rain to the top half of the North Island around 5th-6th, also the west coast of the South Island and Southland. A tropical depression develops in March's second week affecting the Cook Islands and is followed by widespread rain across the top half of the North Island. The last potential for an extreme system is in March's fourth week, when the tide will be the second highest for 2015 and an unsettled system comes through the Southern Cooks and affects the North Island after the 22 March.
Heat wave temperatures may come in the first week of January, mid and end of January, first and last weeks of February and mid March. These may affect many regions, including Auckland, Marlborough, Canterbury and coastal Otago, Some of the season's highest temperatures, possibly over 30C, will be in March's second week, generating heat showers.
Times of dry spells to consider for successful and safer outdoor projects, school camps, boat trips etc may be the first week of January for the North Island, but 4th-9th for the South Island, the first half of February for both islands, and the last week of March for all, except the west and south of the South Island and coastal Otago. The second week of April is also dry for both islands, with continuing summer temperatures.
Times to avoid because of unsettled conditions will be the second and fourth weeks of both December and January for both islands, and the last four days of January. The third week in February is also to be avoided. Rain a week either side of mid March may affect North Island campers, whereas it is only around mid March itself that brings heavy rainfalls across the South Island, apart from the West Coast and Southland, which also receive heavy falls in the first and last weeks of March. The first few days of April and the second half of the month are also wet intervals.
Once it gets going it should be a great summer. Farmers may be pleased with the adequate rain, periods of good summer heat, and no significantly lengthy dry periods that will have the media calling for drought apart from the first half of February. There will be the potential for some flooding and high winds especially in February and March, because next year those will be some of the months that the moon drifts closer to earth. The moon will start to drift further away in April which will bring the onset of our next El Nino. The driest month of 2015 for New Zealand is expected to be May.
Ken Ring of www.predictweather.com is the author of the Weather Almanac for NZ for 2015 (Random House publisher)