Atlantic season's 1st tropical storm forms near Belize
But the center said the the storm could reemerge in the Gulf of Mexico and regain intensity Sunday.
At 8 p.m., the center of Arthur was over the Yucatan Peninsula, about 55 miles (90 km) west of Chetumal, Mexico, and about 175 miles (285 km) east of Ciudad del Carmen, Mexico.
It was moving west-northwest at about 7 mph (11 km/hr) and was expected to make a gradual turn to the west later in the night.
Arthur is expected to weaken to a tropical depression Saturday night but could regain tropical strength if it moves back over the warm Gulf waters, the hurricane center said.
The storm's maximum sustained winds were near 40 mph (65 km/hr), with higher gusts, mainly over water east of its center. Tropical storm-force winds extend outward up to 260 miles (415 km) from the center of the storm, forecasters said.
The government of Belize issued a tropical storm warning for the nation's coast, and the government of Mexico issued a tropical storm warning from Cabo Catoche south to the border with Belize.
A tropical storm warning means tropical storm conditions are expected within the warning area -- in this case, within the next six to 12 hours.
The storm was forecast to dump up to 10 inches of rain over Belize, up to 15 inches in isolated areas, the hurricane center said.
The 2008 Atlantic hurricane season begins Sunday.