El Nino means cooler summer

Don't put away the winter woollies and break out the swimsuit quite yet.

NIWA's prediction for Manawatu and Horowhenua is for a cool summer ahead, with below-normal temperatures, but average rainfall.

"Three-month rainfall totals and soil moisture levels are expected to be near normal, with stream flows likely to be normal or below normal," its three month prediction for December to February said.

The El Nino weather pattern strengthened in October and November – bad news for those who like a hot summer.

NIWA's National Climate Centre principal scientist Brett Mullan said to expect more southeasterly winds, which meant cooler, wetter weather for Manawatu, Rangitikei and Horowhenua, and drier conditions in regions like Hawke's Bay and Wairarapa.

"For the region Taranaki to Wellington, it doesn't mean there won't be warm days this summer, but there will be a number of noticeably cooler days too," Dr Mullan said.

Too early to clean out the fireplace then? Even though we are in December there could be some cold days to come yet, he said.

Dr Mullan said NIWA believed El Nino would persist at moderate intensity through the 2009/10 summer before weakening during autumn.

The centre reminded people the predictions were "probabilistic" and related to the entire three-month period. That is, scientists assessed the probability of conditions and rated them as being above normal, normal, or below normal for the time of year.

"The temperature has to be only half a degree lower to get a `below normal'," Dr Mullan said. NIWA said all outlooks were for the three months as a whole and there would inevitably be wet and dry days, hot and cold days, within a season.

The exact range in temperature and rainfall within each of the three categories varies with location and season.

According to the latest outlook, NIWA said sea-level pressures were likely to be higher than normal to the north of the country and lower than normal to the south, resulting in stronger than normal southwesterlies over New Zealand.

- © Fairfax NZ News