Eastern parts of the South Island, which are on the verge of a drought, probably will not benefit from heavy rain over Fiordland and the West Coast, MetService says.
The South Island had well-below normal rainfall last month, with some farmers in Otago already selling off their stock in anticipation of drought.
MetService had predicted heavy rainfall for the West Coast today.
But forecaster Mads Naeraa-Spiers said it was unlikely to spread to eastern areas.
"This is driven by very moist north-westerlies and the Southern Alps act as a complete barrier for much of this rain so it doesn't really make it over to the east, where they really could do with some now."
Mr Naeraa-Spiers said a few light showers were possible on Tuesday and Friday, although not enough to break the near-drought conditions.
Water short in Dunedin
The dry weather has forced the Dunedin City Council to ask residents to conserve water.
The council said water levels in the area's river tributaries were dropping and people should only use water for necessities until there was rain.
Metservice said Dunedin had received less than one millimetre of rain since New Year's Day.
The city's average January rainfall is 83 millimetres.
The council said if some residents wanted to water their gardens, they should use a hand-held hose, not a sprinkler, and do it after 8pm at night.