Yet another sub-tropical air flow is spreading down across the country – bringing more bursts of rain, and isolated downpours, across northern and western areas of both islands across the next two days. A weak system in the Tasman Sea is helping pull down the moisture rich, warm, air – working in conjunction with a large high near the Chatham Islands.
Rain, with some quite heavy falls but only in isolated pockets, will move back to the South Island’s West Coast on Friday morning. Franz Josef is again in the firing line for some very heavy downpours, but the front does look more broken up than the one last week that brought flooding. Isolated flooding is still possible along the West Coast though.
The heavy downpours for the West Coast don’t stop until the early hours of Saturday.
Meanwhile later into Friday afternoon and evening rain spreads into northern and western areas of the North Island.
Heavy downpours will be hit and miss but rain is expected to continue across the upper North Island, especially the north eastern corner, across Saturday. This is due the rain band slowing down as it tracks east across the North Island and into blocking high pressure east of the island.
Flooding is a possibility with any sub-tropical bursts of rain – but it’s usually quite localised. In the past year or two narrow sub-tropical bursts of rain have brought sudden flooding – last week to Franz Josef, the week before to Whitianga, and last year to the West Coast and Wanganui City as other examples. Generally these rain bands don’t bring widespread problems – but the localised flooding can be quite intense if it occurs. Our blocking mountains and ranges often add to the flooding risks brought on by sub-tropical downpours.
Showers and long dry spells are likely on Sunday.
Risks for possible flooding are highest on Friday and into the early hours for the West Coast, late Friday and into Saturday morning for Nelson and and overnight Friday and across Saturday for the upper North Island.
While there are some isolated flooding risks, it’s important to note that for the most part WeatherWatch.co.nz expects rain to be below flooding criteria for most places.
Images / Weathermap.co.nz