Earthquake victims buy groceries at an improvised store in Camp Corail, north of Port-au-Prince, on Monday. (Eduardo Munoz/Reuters)

Relief organizations in Haiti are scrambling to prepare as tropical storm Tomas swirls toward the island nation that is struggling to recover from January's devastating earthquake and a recent cholera outbreak.

A U.S. navy vessel, the amphibious warfare ship Iwo Jima, was steaming toward Haiti on Tuesday to be on hand to provide disaster relief in case tropical storm Tomas appears late in the week as forecast, possibly after strengthening again into a hurricane. The storm has already caused 14 deaths in the eastern Caribbean.

Aid groups are rushing to do what they can but are already short of supplies after dealing with the catastrophe inflicted by the Jan. 12 quake.

Tomas would be the first major storm to strike Haiti since the earthquake killed as many as 300,000 people and forced millions from their homes. It would also be the first tropical storm or hurricane to hit since 2008, when the storms Fay, Gustav, Hanna and Ike battered Haiti in the space of a month, killing nearly 800 people and wiping out 15 per cent of the economy.

Supplies needed: UN

Even before Tomas hits, there are shortages of 150,000 tarps as well as soap, hygiene kits, field tents, radios and oral rehydration salts for treating cholera, United Nations Humanitarian Co-ordinator Nigel Fisher said.

"We need emergency shelter. We need water and sanitation supplies," Fisher said.

Warehouses are being emptied of existing stocks of rope and tarps to help people in camps, said Imogen Wall, spokeswoman for the United Nations Office for the Co-ordination of Humanitarian Affairs.

Piles of rubble and partially collapsed buildings from the quake still fill Port-au-Prince, the capital. Reconstruction is grinding along without promised aid funds, including $1.15 billion promised by the United States.

A woman walks by damaged power lines and infrastructure after tropical storm Tomas affected St. James parish, Barbados, on Saturday. (Chris Brandis/Associated Press)

As of 11 p.m. ET, Tomas was in the central Caribbean with maximum sustained winds of 65 km/h, according to the U.S. National Hurricane Center in Miami. Its centre was about 620 kilometres south-southwest of Port-au-Prince and moving west at 13 km/h.

Tomas is expected to strengthen over the next 48 hours, and could eventually regain hurricane strength, the U.S. National Hurricane Center said.

Forecasters said officials in Jamaica, Haiti and the Dominican Republic should monitor the storm's progress, because Tomas "could pose a significant threat to these areas later in the week."

Jamaica's government issued a hurricane watch Tuesday afternoon.

As a hurricane on Saturday, Tomas caused at least 14 deaths in a cluster of islands in the eastern Caribbean. St. Vincent Prime Minister Ralph Gonsalves described the damage as "the worst we have seen in living memory." At least eight died in St. Lucia.

Tent cities at risk

In Haiti's refugee camps, many people said Monday that they didn't know Tomas might be coming, but there was little they could do living in flimsy shelters to protect themselves.

"I didn't know about [the storm]. Maybe somebody came by to say something yesterday when I was out," said Florence Ramond, a 22-year-old mother and food vendor who is living on the Petionville Club golf course in a refugee camp managed by actor Sean Penn's relief organization.

Even knowing, Ramond said, she could do nothing to secure her home, a shack made of tarp, wood and a tin door. The roof blew off in an unnamed Sept. 24 storm that ripped through the capital, killing at least five people and damaging thousands of tents.

"They always go around and tell us to tie the tarps up, but I don't have a rope," she said.

With files from CBC News