Climate Update 47 - May 2003

May

Climate

River flows

Soil moisture

Three-month outlook

Checkpoint

Backgrounder

Backgrounder

Backgrounder

ENSO signal approaching neutral
The current warm phase of the El Niño-Southern Oscillation has ended and is not expected to influence New Zealand’s climate over the next few months.
Most forecast models of the development of the El Niño-Southern Oscillation are predicting neutral conditions through late autumn and winter.
Sea surface temperatures around New Zealand were above average at the end of the month.

Mean sea surface temperature departures from normal.
Update on the SOI
The mean Southern Oscillation Index (SOI) for April was -0.6, with the three month

Checkpoint

Outlook and outcome – February 2003 to April 2003
Rainfall was near or below normal as predicted in most regions, but above normal in a few areas of the northern North Island. It was drier than expected in the southwest North Island.
Temperatures were near or below average in most regions as expected.
Higher than expected river flows occurred in Northland, Coromandel, East Cape, Hawkes Bay, and north and mid Canterbury.

May

Climate Update is a summary each month of New Zealand's climate, including soil moisture and river flows.
May 2003 – Number 47
April’s climate: Rainfall was very low in western areas.

Climate

New Zealand Climate
Very dry in western regions
Most of the South Island west coast and some alpine areas recorded just a third of normal rainfall in April. Only half normal rain fell in most other western regions from Waikato to Fiordland, as well as in central Wairarapa, Wellington, central Marlborough, Otago, and Southland. It was drier than normal also in south Auckland, Taranaki, and King Country.

Three-month outlook

The outlook for May to July 2003
A relatively mild early winter is expected, with above average local sea surface temperatures. For May-July, temperatures are expected to be above average over the North Island and north of the South Island, and average or above average over the rest of the South Island.
Normal or below normal rainfall is expected in the east of both Islands, with near normal rainfall likely elsewhere.
Soil moisture levels are predicted to be normal in most regions, but normal or below normal in the western North Island and northern South Island.

River flows

New Zealand River Flows
Extremely low April flows in the central North Island and Southern Alps
April streamflows were high in parts of Northland, Coromandel, East Cape, and north and mid Canterbury, but below normal elsewhere. Extremely low or record low flows occurred in the catchments in the central North Island, Southern Alps, and Southland

Soil moisture

Soil moisture
Very dry soils
There were still significant soil moisture deficits at the end of April in the southwest of the North Island, and in Marlborough, south Canterbury, and much of east and Central Otago.
Some areas that were particularly dry at the end of March, including eastern areas of the North Island and the South Island east coast from Kaikoura to north Canterbury, recorded improved moisture levels during the month after near or above average rainfall.

Soil moisture deficit in the pasture root zone at the end of April (right) compared with the deficit at the same time last year