Major rainmaker to hit South Island tomorrow, second system brewing

A moisture-packed weather system is forecast to slam into the south tomorrow – with another big rainmaker potentially on the cards for next week.
MetService has issued an orange rainfall warning for Westland, where as much as 250mm could drop in the ranges – with peak hourly rates of up to 25mm – between 6pm Thursday and 4pm Friday.
The forecaster warned that areas near the coast could receive as much as 120mm over the 22-hour period.
Heavy rain watches were also in place for Fiordland from noon tomorrow, and in Buller and Grey districts – along with Tasman northwest of Motueka – on Friday.
The agency also advised that gale-strength northwesterlies were possible in eastern areas of the South Island and the southern North Island.
Strong wind watches have been issued for the Canterbury high country, Fiordland, Queenstown and Southland west of Lumsden.
MetService meteorologist Alex Holden said a low pressure system was moving in off the Tasman Sea.
“It’s managed to grab a good stream of moist air from the subtropics and is just directing it straight onto the mountains and producing a lot of rainfall there.”
Holden recommended people keep a close eye on MetService’s forecasts for any upgrades to warnings, as well as the New Zealand Transport Agency’s website.
“We see that with heavy rainfall like this, driving conditions can be quite hazardous, and we’ve also seen infrastructure impaired by these sorts of events over the last few months.”
Warm sea surface temperatures in the West Pacific, currently tracking one to two degrees above normal, were a rainfall factor.
“That will definitely be energising [the system], making it moister and a better rain-producer.”
The front was forecast to weaken as it moved onto the North Island on Saturday.
Meanwhile, Holden said forecasters were watching another low pressure system building below New Zealand, and potentially arriving as a second moisture-charged system next week.
“From what I can comment on at the moment, it looks like a very similar scenario to what’s going to be happening over the end of this week.”