The storm is expected to leave the northwestern Bahamas later on Saturday and then will move well offshore of the east coast of Florida and into the Atlantic Ocean through early next week, according to the US National Hurricane Center.

Humberto had maximum sustained winds of 85km/h with higher gusts, and was expected to become a hurricane by Sunday night, the Miami-based NHC said on Saturday.

It barely moved during Saturday morning, the NHC said, and was located about 45km east-northeast of Great Abaco Island. It was forecast to resume a slow motion towards the northwest and north later in the day.

Forecasters said the storm could drop up to 15cm of rain in some areas but that it was not expected to produce significant storm surge in the northwestern Bahamas, which were hammered earlier this month by Hurricane Dorian.

Humberto could, however, hamper relief efforts in the area where thousands of structures were flattened and 70,000 people were left needing shelter, food and water and medical aid.

Dorian slammed into the Bahamas on September 1 as a Category 5 storm, one of the strongest Atlantic hurricanes ever to hit land, packing top sustained winds of 298km/h.

Bahamian Prime Minister Hubert Minnis has said the official death toll from Dorian stands at 50 but that hundreds of people are missing and it is expected to rise.

United Nations Secretary-General Antonio Guterres arrived in Nassau on Friday in a show of international support. He met with evacuees at a shelter and told reporters Dorian should be a wake-up call for the world about the dangers of climate change.

"If we don't reverse the situation we'll see tragedies like this one multiplying and becoming more and more intense, more frequent," Guterres said. "Climate change is running faster than what we are. We need to reverse this trend."

Australian Associated Press