The U.S. National Hurricane Center in Miami said that Tropical Storm Adrian's center could strike near the Guatemala-El Salvador border on Thursday, bringing torrential rains to an area where past flooding has often been devastating.
By midday Wednesday, Adrian already had maximum sustained winds of 60 mph and it was centered about 270 miles southwest of the coastal border between Guatemala and El Salvador.
It is headed northeast, directly for the coast, at nearly 9 mph, and forecasters said it could reach hurricane force of 74 mph before making land. The storm's outer bands were already bringing rain to parts of Guatemala on Wednesday.
Adrian grew from a tropical depression into a tropical storm Tuesday afternoon.
The executive secretary for Guatemala's disaster prevention agency, Hugo Hernandez, said that officials were getting set for evacuations and to set up shelters for some of the 400,000 people living in high-risk parts of southern Guatemala.
Guatemala and El Salvador banned all maritime activity along their Pacific coasts, calling on fishermen to return to port.
"We are concerned, though we hope that Adrian changes direction and drops in intensity," said Hugo Arevalo, spokesman for Honduras' emergency commission, which declared a state of alert Tuesday evening.
Many rural Central Americans live in flimsy houses on hillsides or near rivers, so storm-caused flooding can cause disasters. In 1998, Hurricane Mitch, arriving from the Caribbean, killed at least 9,000 people in Central America.
Most Pacific storms tend toward the northwest, marching roughly parallel to the coastline and then edging out to sea or veering inland.
The Hurricane Center said that since 1966, only one tropical depression has ever hit the coasts of Guatemala or El Salvador in May and none have done it so early. The Eastern Pacific hurricane season only began on Sunday.
The Hurricane Center said there was some chance the storm could survive a passage across Central America and emerge, weakened, in the Caribbean as a tropical depression.