(CNN) -- Tropical Storm Arlene picked speed late Wednesday as it approached Mexico's eastern coast, the National Hurricane Center reported.
Mexican authorities issued storm warnings as Arlene advanced toward a Thursday morning landfall, possibly close to hurricane strength.
Arlene, the first named storm of the 2011 Atlantic hurricane season, was moving at about 6 mph, packing sustained winds of 60 mph.
At 11 p.m. ET, the storm was about 90 miles east-northeast of Tuxpan and about 125 miles east-southeast of Tampico.
"Tropical storm conditions have likely reached portions of the warning area and will continue to spread onshore through Thursday morning," the weather service said.
Authorities in the Mexican states of Tamaulipas, Veracruz, San Luis Potosi and Nuevo Leon braced for heavy rains. Forecasters from the National Hurricane Center warned of possible flash floods and mudslides.
"With any storm of this size, it's easy to overlook it and call it insignificant," said CNN meteorologist Chad Meyers. "The major effect with this storm will not be wind damage, but will be inland flooding from up to 12 inches of rain in the mountains of Mexico."
The hurricane warning in Mexico stretches from the eastern coastal town of Barra de Nautla north to La Cruz. Authorities have also issued a tropical storm warning from La Cruz north to La Pesca, and from Palma Sola south to Veracruz.
Meyers added that while Mexico's major northeastern city of Monterrey should be just north of the maximum rainfall, Victoria "may be right in the middle of the bull's-eye."
It is expected to produce 4 to 8 inches of rain in some areas, while higher amounts of isolated rainfall will likely fall in mountainous terrain and could cause life-threatening flash floods and mud slides.
When Arlene makes landfall, the storm surge could raise water levels up to 2 feet above normal tide markers.
The Atlantic hurricane season spans June 1 to November 30.
CNN's Sean Morris, Chad Meyers, Mari Ramos, Ed Payne and Sarah Dillingham contributed to this report.