A wet, windy weekend is on the way with a heavy rain warning and severe watch issued for Nelson and warnings to clear storm water grills.

At 10am today a heavy rainfall warning for the ranges of Buller and Nelson was released, following on from last night's severe weather watch.

''From tonight (Friday) the front is expected to bring significant heavy rain to the ranges of Buller and northwest Nelson, where 300mm of rain may accumulate,'' its forecaster said.

a severe weather watch was upgraded to a weather warning for Nelson, with ''a heavy rainfall warning is now in force for the ranges of Buller and Nelson.''

Last night the MetService issued a severe weather watch for Nelson, Westland and Buller last night with strong winds and heavy rain expected to hit at the weekend.

A heavy downpour was forecast to reach western Nelson tomorrow with the front moving over the city on Sunday, followed by a strong northwesterly winds and heavy rain.

''Rainfall accumulations in these areas are likely to exceed warning amounts and (will) be added to the Severe Weather watch closer to the event,'' the Met Service warning said.

The Nelson City Council has warned residents to clear leaves and other rubbish from any stormwater grills near their property.

''If sumps are blocked, rain water can quickly build up, adding to the risk of flood damage,'' said Alec Louverdis, executive manager network services.

Elsewhere in the South Island, a heavy rain watch has been upgraded to a warning in the Westland ranges south of Otira and the Otago and Canterbury head waters.

The heaviest falls were likely to be in the ranges of Westland, where 500 millimetres of rain may fall.

The headwaters of the Canterbury lakes and rivers are likely to receive significant spill-over rain, with 100mm of rain forecast today.

- © Fairfax NZ News