Heavy rain, severe gales, coastal flooding closing in

Wednesday, 3 January 2018

The weather’s taking a turn for the worse.

A rapidly deepening low bearing down on the country is expected to bring heavy rain to many areas, severe gales and a risk of coastal flooding on Thursday and Friday.

In Auckland, similarities are being drawn between the coming storm and ex-tropical cyclone Ita that caused the inundation of Tamaki Dr in April 2014.

Whether Tamaki Dr would be inundated again was still to be determined, Niwa principal scientist - forecasting Chris Brandolino said. 'But it's certainly in the conversation.'

Lightning bolts at a wind farm near the Manawatū Gorge.

Niwa Weather said a forecast for strong northeast winds meant king tides at 10.15pm Thursday and 10.49am Friday were the ones to watch.

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'It depends basically on how the winds align at the time of high tide,' Brandolino said.

MetService is warning the heaviest rain is expected in Northland, Auckland, Coromandel Peninsula, Bay of Plenty, Mt Taranaki, Marlborough and Nelson.

Strongest winds are expected across the upper North Island from Taranaki to Bay of Plenty northwards, with gusts of up to 120kmh in exposed places. Severe gale-strength northeasterlies are also possible in exposed areas of the rest of the North Island.

In Northland, many areas could get at least 50mm of rain in the 12 hours from 9pm Thursday, with up to 120mm possible in the northern and eastern hills.

In Auckland, the worst of the rain is expected in the 12 hours from noon Thursday, with up to 90mm possible, particularly about the Hibiscus Coast and the ranges.

Coromandel Peninsula could get up to 150mm in 13 hours from 1pm Thursday, Bay of Plenty could get up to 160mm in 15 hours from 3pm, Mt Taranaki could get up to 150mm in nine hours from 6pm, Nelson could get up to 160mm in nine hours to 9am Friday, and Marlborough and the Kaikōura Coast could get up to 150mm in the nine hours to 9am.

The worst of the winds are expected in Northland from 4-9pm on Thursday, in Auckland from 6pm to midnight Thursday, and in Coromandel Peninsula, Waikato, Waitomo, Taumarunui, Bay of Plenty, Rotorua, Taupō and Taranaki in the nine hours to 6am Friday.

Rain may also become heavy in the area from Waikato to Taranaki, excluding the mountain, and also the central North Island high country.

A combination of strong winds and high tides could cause coastal inundation in eastern areas from Bay of Plenty north, MetService said.

Before then, most of the country has a chance of thunderstorms after lunch on Wednesday.

There's a chance of at least isolated showers everywhere on Wednesday, and some could be heavy and thundery from afternoon, as a warm humid northerly flow covers the country.

The forecast isn't great for Tauranga, where the third T20 cricket game between New Zealand and the West Indies is scheduled to start at 7pm on Wednesday, after the second game in the series, also in Tauranga, was stopped by rain on Monday night. MetService forecast a showery day, with a risk some could be heavy from the afternoon.

There's a risk of severe thunderstorms for parts of the central North Island, including Taumarunui, southern parts of Taupō, Taihape, the western ranges of Hawke's Bay, and inland parts of Taranaki, Whanganui and Manawatū.

Almost the whole country has a risk of thunderstorms as a combination of warm, humid weather and light winds allows clouds to build up during the day.

For the North Island from Waikato south, but excluding Bay of Plenty and Gisborne, showers are expected to become widespread from afternoon, mainly inland, and downpours are possible.

On Tuesday, MetService counted 2771 strikes by about 9pm, with the two busiest areas being Manawatū with 492 strikes and the Tararua district with 382.

The heaviest rain was reported in that part of the country, with 50-55mm in some MetService gauges and 75-100mm reported by unofficial sources.

Despite that, much of the Manawatū didn't get any rain. 'It is the nature of thunderstorms that a few places get a lot of rain while many others get little to none,' MetService said.

Niwa Weather warned the rule of thumb for lightning was that if you can hear thunder, you're close enough to be struck by lightning.

'Remember to stay off the water/beach when thunderstorms are nearby,' Niwa Weather said.

Auckland is expected to have afternoon sunny spells on Wednesday, with only isolated showers but some could be heavy, and a high of 26 degrees Celsius as the wind turns to the northeast. On Thursday, rain could get heavy and the northeasterlies are expected to be strong.

Wellington is expected to get to 25C on Wednesday, with morning cloud breaking to sunny spells, and a few afternoon showers, mainly in the north. Rain is forecast to become widespread late on Thursday and continue through Friday when strengthening southerlies will cool things down a bit.

Christchurch could have a few light morning showers before becoming fine by afternoon, when the high is expected to reach 25C. It's forecast to stay dry during the day on Thursday, with rain arriving at night and continuing into Friday, which will also be a cooler day thanks to incoming southerlies.