The region's civil defence said the heavy rain would hit from 6pm south of Tolaga and last until lunchtime tomorrow.
MetService this morning upgraded its forecast to a heavy rain warning for northern Hawke's Bay saying rivers and streams could rise rapidly, possibly causing flooding and slips. A strong wind watch is in force for the eastern regions as a deep low passes off the coast of the North Island later today.
"For those that are camping or who have light outdoor furniture or trampolines in the likely affected areas, please make sure you secure them," Civil Defence said.
Despite the dire forecast Rhythm and Vines spokesman Chris Henry said organisers did not think the weather would affect the festival.
Henry said they were expecting some rain but nothing that would dampen the spirits of revellers.
"Pack warm and bring a jacket, but it's not looking like it will affect any of the activities," he said.
However, Gisborne District Council advised campers to delay putting their tents up because of the approaching storm.
Jacqueline Green, manager of Gisborne's Showgrounds Park Motor Camp, said there were a raft of young people in tents, camping out for the Rhythm and Vines festival.
She said they are warning campers of the risks that come with stormy weather.
"We have signs and precautions around saying, in the interest of safety, not to set their tent sites directly up under big trees."
"But they're pretty safe out here 'cause they're close to our residents, so we'll be keeping an eye out on them"
Green says they've had about 20 cancellations, but most campers are just battening down the hatches for a stormy night.
"The weather seems to have not put them off at all, we have had a few cancellations but they're still coming."
MetService said squally thunderstorms laced with hail were due to move up the East Coast of the North Island today.
Parts of the Hawke's Bay north of Mohaka is bracing for up to 100mm of rain and intense downpours overnight. Southerly gales of more than 90 km/h are due to hit late this afternoon.
A coastal storm warning was in place with towering 5m swells expected to batter the coastline between Cape Kidnappers and East Cape.
MetService said despite big swells, the gale-force wind means it was not looking great for surfing until the weekend.
In the centre of the North Island snow was expected to fall on the volcanic peaks with wind chill dropping the temperature to a chilly minus 12C.
The stormy weather is expected to pass by late tomorrow.
