Tropical Storm Matthew formed in the southern Caribbean on Thursday, and threatened to strengthen into a hurricane as it headed west over warm water towards Central America.

The region is facing one of the most intense rainy seasons in the last 60 years, with flooding and landslides that have killed more than 300 people and caused serious damage.

Matthew is forecast to make landfall near the Nicaragua-Honduras border late Friday or early Saturday, and authorities are bracing for more flooding as soil across much of Central America is already saturated with water from the season's earlier storms.

At 2100 GMT, the center of Matthew was about 435 miles (700 kilometers) east of Puerto Cabezas, Nicaragua, packing maximum sustained winds of 40 miles (65 kilometers) per hour, with higher gusts, the Miami-based National Hurricane Center said.

"Additional strengthening is forecast during the next 48 hours, and Matthew could become a hurricane by Saturday," the NHC said, adding that the storm was moving towards the west at 16 miles (26 kilometers) per hour.

Matthew is expected to dump between six and 10 inches of rain over parts of Nicaragua and Honduras, with up to 15 inches possible in isolated areas.

"These rainfall totals may produce life threatening flash floods and mud slides," the NHC said.

A storm surge "is expected to produce some coastal flooding near and to the north" of the area the center of where Matthew makes landfall. "Near the coast, the surge will be accompanied by large and dangerous waves."

On its forecast track, the center of Matthew will graze the northern coast of Honduras, then cross water again in a northwesterly direction and strike Belize on Tuesday, and Mexico's Yucatan peninsula the following days.

Since the arrival of Tropical Storm Agatha in late May, heavy rain has caused destruction in Guatemala, Nicaragua, Honduras and El Salvador.

Costa Rica, Honduras and Nicaragua all declared states of alert. Only Panama will be spared in the region.

Guatemalan President Alvaro Colom declared a "state of national emergency" on Saturday due to the heavy rain and flooding. At least 36 people have been killed in Guatemala, 40 people are missing, and some 11,500 evacuated by the flooding, which has caused some 1.5 billion dollars in damage.

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