Hurricane Tomas is lashing earthquake-ravaged Haiti with high winds and rain, and forecasters have warned of flooding and dangerous conditions.

The U.S. National Hurricane Center says the center of the storm is expected to pass west of Haiti on Friday. 

Forecasters warn that Tomas, with winds of 135 kilometers per hour, could dump up to 25 centimeters of rain in some areas, triggering life-threatening flash floods and mudslides. But the country is not expected to suffer a direct hit.

Government officials are urging residents in at-risk zones to seek emergency shelter, and aid groups have been working all week to move the survivors of January's earthquake to safety. But some residents in the sprawling tent camps in Port-au-Prince have remained, fearing they will lose all their possessions if they leave, or will be barred from returning to the makeshift camps.

The massive quake displaced more than a million people.

U.N. health officials warn that polluted flood waters and unsanitary conditions from the storm are likely to worsen Haiti's cholera outbreak, which already has killed more than 440 people.

Hurricane warnings are in effect for Haiti, the Bahamas, the Turks and Caicos islands, and the province of Guantanamo, Cuba. 

Aid groups are stockpiling supplies across the nation. The U.N. has asked the international community for emergency aid, saying a half-million people could be affected by the storm.

The U.S. Navy has sent the USS Iwo Jima to Haiti to help provide humanitarian support. The ship carries medical experts, engineers and helicopters.