The worst of the wet weather should be over by dawn tomorrow, Hokitika weather observer Mark Crompton says.
The heaviest rainfall is expected this evening and especially after midnight.
Mr Crompton said the Metservice was still predicting rainfall of up to 300mm inland.
"That's in addition to what's already fallen. The problem is, if we get this heavy burst tonight, it's going to be falling into catchments that are already totally saturated," Mr Crompton said.
"There's certainly scope for flooding."
Warnings are in place for State Highway 6 from Hokitika to Haast, SH73 from Otira to Harris Creek and SH7 from Kaiata to Greymouth where wind and rain are causing surface flooding and creating danger for high-sided vehicles and motorcyclists.
Meanwhile Gusts of more than 100kmh have begun to arrive in the Wellington region as a "bomb low" weather pattern arrives.
Wellington City Council report the gusts of wind have toppled a traffic light at the intersection of Taranaki St and Dixon St, while a power pole has been blown over on Aotea Quay.
At the capital's airport some flights leaving the city after 6pm were slightly delayed as they managed the strong winds.
Strong wind warnings are in place for Wellington, where 160kmh northwest gusts are expected in exposed spots, while Wairarapa, Marlborough, and north Canterbury were in for 150kmh gusts.
Shortly after 5pm on Wednesday, MetService was recording gusts of more than 100kmh on the State Highway 2 Rimutaka Hill Road peak. It was expecting winds to peak in Wellington on Thursday morning.
