Tropical Storm Alex is gaining strength as it swirls across the Gulf of Mexico on a path towards Mexico's north-eastern coast.
The storm could have strengthened to a hurricane by Tuesday and its heavy rains are expected to begin lashing the Mexican states of Tamaulipas or Veracruz around midweek, according to the US National Hurricane Centre in Miami.
It is currently on a course well clear of the massive oil spill from the BP deepwater rig in the Gulf.
The storm's heavy rains caused flooding and mudslides that left at least four people dead in Central America over the weekend, though Belize and Mexico's Yucatan Peninsula appeared largely unscathed.
It made landfall in Belize on Saturday night with winds at 60mph. But it weakened into a depression on Sunday as it crossed the Yucatan Peninsula. Once over the warmer waters of the Gulf of Mexico, Alex quickly grew back into a tropical storm with winds of up to 45mph. The hurricane centre said it will keep strengthening over the coming days.
The centre said rains from Alex will keep falling on southern Mexico and Guatemala until Tuesday and warned of life-threatening floods and mudslides.
The heavy rains prompted a landslide in north-western Guatemala that dislodged a large rock outcropping, killing two men who had taken shelter from the storm, according to the national disaster response agency.
In El Salvador, civil protection chief Jorge Melendez said two people were swept away by rivers that burst their banks. About 500 people were evacuated from their homes.
Authorities in Guatemala and Belize are keeping an eye on rising river levels. One bridge in western Belize was swamped entirely, cutting off a remote Mennonite community.
Hundreds of Belize residents and tourists who had fled low-lying islands for shelters on the mainland began returning on Sunday. The country apparently avoided major damage, emergency co-ordinator Noreen Fairweather said.