Weather: Heavy rain, flight disruptions feared as 'tap of tropical moisture' opened on New Zealand

The weekend's sunshine won't last as a surge of heavy rain and strong wind makes its way toward New Zealand.

A worrying NIWA graphic shows a "moisture anomaly" approaching as the "tap of tropical moisture" is opened up from the tropical Indian Ocean.

"What does this mean for us? Heavy rain is likely to affect the western South Island starting later Sunday before spreading into the top of the South Island and North Island from Sunday night into Monday," NIWA warns.

This rain is coming into regions already hit by the recent deluge which caused slips and flooding.

"Areas that have recently received heavy rain may experience further impacts during this short-lived event," MetService warns.

"We have issued heavy rain watches and warnings for some western and northern South Island regions, beginning Sunday evening."

Strong, gusty winds will accompany the heavy rain, with possible wind damage across many regions. A strong wind warning is currently in place for Fiordland from Sunday afternoon, where northeasterly winds may approach severe gale at times.

"The rough weather may impact flights in both nations (especially turbo-prop planes and smaller airports) with some highways impacted too," WeatherWatch warns.