Summer's coming to an end - rain on the way

NZ Herald,
Publish Date
Wednesday, 6 March 2019, 3:24PM
Forecasters say there will be a wet end to the month and week. (Photo / NZ Herald)
Forecasters say there will be a wet end to the month and week. (Photo / NZ Herald)

A rainy end to the month will bring some welcome wet to many regions still parched from New Zealand's third warmest summer on record, forecasters say.

Niwa meteorologist Ben Noll said weather across the North Island and the upper South Island could turn "busier" over the last two weeks of March and into April.

"At this point, that's what we are watching out for," he told the Herald.

"The Tasman Sea is looking like it will become much more active around then, with a lot of excess heat and energy waiting to be released."

Noll said ocean heat that had built up over summer could well invigorate a series of low pressure systems expected at the back end of the month and in early April.

"We do have a lot of warm, moist air still about and it wouldn't be unexpected if one of these fronts due in a couple of weeks produced a lot of rain."

There was a good prospect of rain for the Nelson-Tasman region, which had just endured one of its driest seasons on the books, with a 40-day dry spell and a paltry 64mm of rain recorded across the whole of summer.

The latest drought index showed that region, along with the tip of the North Island, were in "severe drought".

Taranaki and parts of Waikato, Whanganui-Manawatu and the Bay of Plenty were "extremely dry", while Northland, Auckland, Coromandel, King Country and the Lower North Island were all deemed very dry.

In the shorter term, rain forecast for Friday could bring the wettest day of the year so far for areas in the North Island, including Auckland, Waikato and Taranaki.

"We are talking about areas that could really use it, but obviously, too much, too fast is never a good thing," Noll said.

A moist northerly flow was forecast to strengthen over New Zealand ahead of a front forecast to move northwards across the South Island on Thursday and across the North Island on Friday.

Source / MetService

Source / MetService

MetService reported a "moderate confidence" of rainfall accumulations reaching warning criteria in southern Westland and Fiordland tomorrow.

There was a low chance that a rainfall warning would be needed for Mt Taranaki on Friday and the eastern ranges of Bay of Plenty on Friday and early Saturday.

Tomorrow, there was also low confidence that a wind warning will be issued for Southland, western Otago and the Canterbury high country south of about Mt Cook.

On Saturday, a ridge of high pressure should spread over central and southern New Zealand, while a trough remains slow-moving over the north of the country.

By Sunday, the ridge was expected to cover most of New Zealand.

At least one ex-tropical cyclone had been forecast to come within 550km of New Zealand this season, and although this hadn't transpired yet, Noll said there was no reason to say it wouldn't happen.

Meanwhile, temperatures were expected to linger in the above-normal range across all regions until winter.

Yesterday, Niwa announced the summer of 2018-19 came third on the record books for warmth, largely due to above-average sea temperatures around New Zealand's coastline.

Marine heatwave conditions persisted in the Tasman Sea and coastal areas of Hawke's Bay and Canterbury experienced marine heatwave conditions for part of summer.

The warmest summer on record was 2017/18 and the second warmest 1934/35, both of which were characterised by significant marine heatwave events.

One new paper co-authored by New Zealand scientists showed species around the world would suffer as these events grew in frequency and intensity under climate change.

Source / Niwa

Source / Niwa

The highest temperatures of summer were in the Bay of Plenty, Waikato and Coromandel.

But the top temperature of summer went to Hanmer Forest with 38.4C on January 31 – the warmest on record for this station.

Hamilton and Tauranga went for 36 days straight without rain – both experiencing their third longest dry spell on record.

In addition to the warm seas, summer air flow patterns also favoured warm temperatures with a distinct lack of southerlies throughout the season.

December was characterised by the prevalence of warm and moist easterly and northeasterly winds, while frequents bouts of high pressure occurred in January and February.

Most notably, the combination of high pressure and hot air masses originating from Australia led to prolonged hot conditions throughout much of New Zealand to the end of January.

The dry and sunny weather was influenced by a central Pacific El Niño event.

Several locations across the country observed record or near record high daily maximum and minimum summer temperatures during this time.\

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