The MetService warned such rain may cause rivers and streams to rise rapidly, with slips and surface flooding possible. Severe gale southerlies could also bring down trees and powerlines in exposed areas, and make driving hazardous for high-sided vehicles and motorcycles.
The heaviest falls were expected last night and early today, when the intensity of the downpours could reach 25-35mm an hour, she said.
That could rise to 45mm of rain an hour in the event of thunderstorms.
Today will see rain clearing late afternoon and southerlies easing.
Conditions will clear in time for the weekend, with 21C highs predicted for Saturday and Sunday.
Federated Farmers Hawke's Bay president Will Foley said local farmers were welcoming the sight of the rainfall.
"It's a real positive for farmers; after a dry winter the regular top-ups have allowed a lot of farmers to catch up with establishing crops and increasing yield."
He said the rain meant farmers could begin to conserve feed in preparation for El Nino this summer.
"This was a real concern in September but those fears have now been alleviated," Mr Foley said.
