A large slow moving low over the Tasman Sea is expected to direct a strong, moist northeasterly flow and rain onto northen and western parts of the country today. It is then expected to cross over to lie east of central New Zealand on Wednesday and direct rain onto eastern areas of the South Island and the lower North Island.
In the north of the country, patchy heavy thundery rainfall is expected to move down through Northland this afternoon, northern parts of Auckland tonight and Coromandel Peninsula and mainly central and western Bay of Plenty from early Wednesday morning. Generally, rainfall amounts look like falling short of warning criteria, but there could well be some localised areas of intense rainfall due to thunderstorm activity. These areas are difficult to pinpoint at this stage. The rain is expected to clear from the north through Wednesday.
There is uncertainty as to where the low will cross the country on Wednesday. The easterly flow has the potential to direct significant rainfalls into Canterbury, Marlborough and Wairarapa. But due to the uncertainty of the position of the low, it is difficult to indentify the main target area. Current guidance would suggest that the heaviest rain may fall in Canterbury and eastern Marlborough and a warning will likely be issued closer to the event.
The previous watch for Fiordland, Westland and Nelson has now been upgraded to a heavy rainfall warning.
These conditions could produce slips and flash flooding, especially in thunderstorms over the north of the country and members of the public are urged to keep up to date with the latest weather information in case further warnings are issued.
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