The search for a missing tramper in Milford Sound has been suspended because of bad weather.

British man Eli Sweeting failed to return from a day trip to climb Mitre Peak on Sunday.

In a social media post, his sister Serena Sweeting expressed her thanks to search crews on behalf of worried family and friends.

"The rest of the family are located in England and this is an incredibly worrying time. Thank you so so much to everyone out there looking for Eli. I feel so hopeless being so far away but it's reassuring the effort going In to find him. If anyone spoke to him please reach out to the police with information," she wrote.

A heavy rain warning and strong wind watch is in place for the area.

MetService is forecasting peak rates of rain of 20-30mm/h for Fiordland about and north of Doubtful Sound on Thursday afternon and evening and said thunderstorms were possible.

The orange level warning said streams and rivers may rise rapidly and surface flooding and slips were possible. There was a minimal chance of upgrading to a red warning.

On Wednesday, search helicopters were unable to take to the air in bad weather but ground searches had continued.

Police said on Tuesday about 60 volunteers, 10 police staff and helicopter and tourism staff were involved that day.

The plan was to resume the search on Friday, they said.

Published by permission