Drier forecast set to put a spring in the step
WITH only a month left until winter is officially over, we can all start looking for the light at the end of the tunnel — spring — which Niwa is forecasting to be warmer and drier than usual.
Niwa forecasting principal scientist Chris Brandolino said very strong trade winds in the equatorial Pacific led to a cooling of subsurface ocean temperatures during July, but this would very likely lead to a restrengthening of La Nina conditions in the coming months.
‘‘The potential for more anticyclones near the country, owing to La Nina, may lead to warmer temperatures, sunshine, and fewer westerly winds than normal during spring.
‘‘This may be associated with an increase in dry spells during the period, particularly in the west of both islands.
‘‘This pattern could limit the number of southerly fronts, but also allow low pressure systems to track towards the country from the northwest from time to time — such systems caused heavy rainfall and flooding during July.
‘‘Overall, this is a shift towards drier conditions relative to previous outlooks.’’
He said warmer than average sea temperatures were also expected to continue to buffer the country from longduration cold.
‘‘Around New Zealand, sea surface temperatures (SSTs) ranged from 0.5degC to 1.3degC above average during July, a decrease compared to June.
‘‘SSTs are forecast to remain above average into spring, which will have an upward influence on air temperatures.’’
Over the next three months (AugustOctober), temperatures on the West Coast, the Alps and foothills, inland Otago, and Southland were very likely to be above average, and more northeasterly winds may cause periods of increased sunshine and warmer temperatures, he said.
Rainfall totals, soil moisture levels and river flows were most likely to be near normal.
However, several heavy fronts were likely during the first week of August, and fewer westerly winds during spring may lead to dry spells.
On coastal Otago, temperatures were most likely to be above average and more northeasterly winds may lead to more cloud cover and warmer overnight temperatures, he said.
Rainfall totals are about equally likely to be near normal or above normal, but there was potential for more frequent onshore winds during spring which could lead to more wet days.
Soil moisture levels and river flows were most likely to be near normal, he said.
‘‘Soil moisture levels and river flows currently range from normal to well above normal across the country due to heavy July rainfall.
‘‘This has contributed to substantial groundwater recharge and a replenishment of water storages.
‘‘The expectation over the next three months is for a return to near normal soil moisture and river flow conditions across the country.’’