Even before the quake Haiti often suffered badly during the rain and hurricane seasons as a result of its poor infrastructure.
In 2008 a series of storms killed more than 800 people.
Now in the capital Port-au-Prince, some 770, 000 quake survivors are living in makeshift camps and with the onset of rains, the threat of disease and infection poses another great challenge.
"We have a huge challenge in terms of just providing emergency shelter - something that we feel that if we put all of our weight behind, as we are doing right now, we will be able (to do)," Kristen Knutson, a spokeswoman for the UN office that is coordinating the international relief effort, told Reuters news agency.
|Brazil's president visited Haiti, pledging more financial assistance [Reuters]
Thursday's deluge hit as relief officials changed strategy on dealing with quake
survivors, delaying plans to build big refugee camps outside the capital.
Instead, they want the homeless to pack up their tents and return to destroyed neighbourhoods.
Gerald-Emile Brun, an architect with the Haitian government's reconstruction committee, told Reuters that "everything has to be done before the start of the rainy season, and we will not be able to do it".
Brun also suggested that Haitians may largely be left to fend for themselves.
Haiti meanwhile is continuing to count the economic cost of the quake.
Call to cancel debt
On Thursday the country's president, Rene Preval, said government assessments had indicated that the disaster would cost the already poor country up to 50 per cent of its gross domestic product.
"This earthquake... led to the deaths of 200,000 to 300,000 people and destroyed from 35 to 50 per cent of the GDP," he said.
Preval was speaking reporters after meeting Luiz Inacio Lula da Silva, his Brazilian counterpart at a UN-Brazilian military base in Port-au-Prince.
During his brief visit, Lula called on the international community to cancel Haiti's debt, and officials from the two governments signed agreements to aid Haitian farmers and schools, which were hard hit in the quake.
According to the United Nations, 5,000 schools were damaged or destroyed in Haiti, which was already the poorest country in the Western Hemisphere before the catastrophe struck.
Lula also referred to a recent South American summit's pledge of $300m in aid for Haiti, including an agreement to create a $100m fund to help the government with immediate needs.