Pacific castaway Jose Salvador Alvarenga is preparing for a faster and more comfortable journey home, after 13 months adrift in a small fishing boat.

Officials in the Marshall Islands said Mr Alvarenga would depart the tiny Pacific nation on Friday for Hawaii, before travelling on to El Salvador or Mexico.

"Most likely he will be repatriated back to El Salvador," foreign affairs official Anjanette Kattil said.

"Initially we thought he was Mexican but even if he was not, the Marshall Islands would render assistance to anyone who washes up on our shores."

Mr Alvarenga was born in El Salvador but had lived for years in Mexico.

He said he set off from there on a fishing trip in late 2012 before becoming lost and drifting some 12,500km to the Marshalls in a small boat.

The 37-year-old said he survived by eating raw fish and birds as well as drinking turtle blood, urine and rainwater for 13 months.

He said a teenage companion named Xiguel starved to death during the ordeal.

Mr Alvarenga's family, including a 14-year-old daughter named Fatima who has no recollection of the father who left for Mexico before she was born, said they were looking forward to welcoming him home.

"It is a divine miracle, a sign that God was compassionate with our son's life," his mother Maria Julia said from her home on El Salvador's Pacific coast.

She said: "I kept thinking that one day he would come back to us, that God wants him to return to our house."

Mr Alvarenga was released from hospital in the Marshalls capital Majuro late last night.

A medical check-up had found he was suffering severe dehydration and the effect of a poor diet, but was otherwise healthy.

After shaving the bushy beard that grew during his months adrift, he is keeping a low profile in a local hotel today, with two policemen guarding his room.

Mr Alvarenga has become something of a celebrity in the Marshall Islands and Ms Kattil said locals had taken him to their hearts.

"People have anonymously arrived at hospital to bring him food, clothes, toiletries and blankets," she said.

The stockily-built fisherman appeared remarkably healthy just days after being found wandering disorientated and clad only in ragged underpants on the coral atoll where his boat washed up.

There were some contradictions regarding dates in various media interviews he has given since being rescued.

However, authorities in Mexico confirmed they launched an air and sea search for him and a missing boy in November 2012.

Fishermen in Mexico's southern Chiapas state also said they remembered Mr Alvarenga, who was known by the nickname "La Chanca" or "fatty".

"We are surprised, but there is no doubt it's him," said fisherman William Uscanga after seeing a picture of the castaway.

El Salvador does not have diplomatic relations with the Marshall Islands but Mexico does, and a Mexican official is due in Majuro today to coordinate Mr Alvarenga's repatriation.

In an interview with AFP from his hospital, Mr Alvarenga said he had suicidal thoughts during his trip. However, he said he was sustained by dreams of reuniting with his family and of eating tortilla and chicken.

His mother was eager to oblige, saying: "We will make him a big meal, but we won't feed him fish because he must be bored of eating that.

"We will make him a big plate of meat, beans and cheese to help him recover," she added.