Climate Update 50 - August 2003

August

Climate

River flows

Soil moisture

Three-month outlook

Checkpoint

Backgrounder

August

Climate Update is a summary each month of New Zealand's climate, including soil moisture and river flows.
August 2003 – Number 50
July’s climate: July was cool and sunny with frequent frosts.
July’s river flows: Low flows follow dry month.
Soil moisture levels: Some soils still await winter top up.
Three month outlook: A mild start to spring is expected.
Checkpoint: How well are we doing with our predictions?
Backgrounder: Snow: a valuable commodity

This issue of the Climate Update is available as a PDF.

Backgrounder

ENSO goes quiet
The Equatorial Pacific atmosphere and ocean surface conditions suggest that the El Niño-Southern Oscillation (ENSO) has moved into a neutral state in July, apparently ending the short-lived cooling (relative to normal) in sea surface temperatures that developed in May.
Most climate forecast models indicate there will be neutral conditions over the next 3 months.

Checkpoint

Outlook and outcome – May 2003 to July 2003
Rainfall occurred as predicted in many areas, particularly the normal or below normal rain in eastern areas. Some localities received above average rain.
Air temperatures were above average over much of New Zealand as was expected. Near average temperatures were recorded at a few locations.
Below normal river flows occurred as predicted in the south and east of the North Island and the eastern South Island.

Climate

New Zealand Climate
Cold, sunny, and frosty
July was colder, sunnier, and more settled and frosty than average, with well below normal rainfall in most areas. July climate patterns were associated with more anticyclones (‘highs’) than average over New Zealand and in the Tasman Sea. As a result, winds were mostly light during the month, and there were low nighttime temperatures, and above average sunshine in most regions.
Record low rain
Parts of the central North Island had the lowest recorded July rainfall. Kawerau and Rotorua received less than 20% of normal rain.

Three-month outlook

The outlook for August to October 2003
A mild start to spring is expected, with above average temperatures in all North Island districts and in the northern South Island. Temperatures are expected to be average or above average over the rest of the South Island. Despite this, some frosty spells are also expected, especially during the first half of the period.
Local sea surface temperatures are likely to remain above average and local circulation patterns are expected to favour enhanced westerly or northwesterly wind flow.

River flows

New Zealand River Flows
Low flows follow dry month
July streamflows were below normal in most of the North Island, Nelson, Marlborough, and the east coast of the South Island. Flows were normal to above normal for rivers in the west and south of the South Island.

Soil moisture

Soil moisture
Some soils still await winter top up
Marlborough, south Canterbury, and Central Otago soils had not received normal winter recharge by the end of July. Soils in parts of these regions were much drier than usual at the end of the month, with deficits of more than half their available water capacity. Soils were at field capacity elsewhere in the South Island and in most of the North Island.

Soil moisture deficit in the pasture root zone at the end of July (right) compared with the deficit at the same time last year (centre) and the long term end of July average (left).