Ex-cyclone’s impact on south uncertain

The weather system related to ex-Tropical Cyclone Uesi is forecast to batter parts of the South Island on Sunday and Monday, but it’s not known exactly what areas will be hit.

Previous models indicated Westland and Fiordland would see the most significant impact, but the exact trajectory of the system was still uncertain, according to MetService meteorologist Andrew James.

‘‘The forecast track is for it to continue moving south and then move around to the southeast towards the southern part of the South Island; where exactly it passes down there is still a little up in the air.’’

However, meteorologists were confident of the weather ahead. ‘‘We’re expecting that there will be heavy rain for at least parts of the West Coast for sure.’’

On Friday morning MetService issued a heavy rain warning for Westland south of Otira from 4am Sunday until 4am Monday. Accumulative rainfall of 180mm to 250mm was expected for the ranges, and 70mm to 100mm near the coast.

A heavy rain watch was also in place for the ranges of Buller and Westland (from Otira northwards), the headwaters of Otago and Canterbury Lakes and Rivers south of Arthur’s Pass, and Fiordland. MetService warned the rainfall amounts could approach warning levels.

Several Numerical Weather Prediction (NWP) models predicted the system would continue to track southeast on Sunday and Monday, potentially resulting in significant impact in Southland and Otago, as well as the western regions.

Wellington, Marlborough, Canterbury and southern Wairarapa were also expected to be affected. MetService forecast a moderate chance of northwest winds approaching severe gales for the regions on Sunday.

The weather system was no longer a tropical cyclone, instead it was classified as a low, or an ex-tropical low. James said it had lost its tropical nature and was behaving differently, but was ‘‘still an intense weather system’’.

‘‘That’s pretty much the normal situation ... as [cyclones] move out of the tropics.’’

The system was currently sitting out in the Tasman Sea between New Zealand and Australia, and wasn’t considered to be fast moving. MetService forecasters were monitoring the system’s movements.