Miami.– The third tropical storm of the 2008 Atlantic hurricane season, Cristobal, gained strength just off the U.S. East Coast on Saturday and gale-force winds and heavy rains were expected to lash the Carolinas as the storm grazed the shoreline on a northeasterly path.

Hurricane Bertha, meanwhile, defied cool Atlantic waters and remained a hurricane while a strong tropical wave south of Jamaica was expected to develop into a depression –the precursor to a storm– as it headed toward Mexico's Yucatan Peninsula and the oil rigs of the Gulf of Mexico beyond.

Cristobal strengthened despite being over only marginally warm waters but was not seen becoming a hurricane, which requires winds of at least 74 miles per hour (119 km per hour), the U.S. National Hurricane Center said.

It was about 125 miles east of Charleston, South Carolina, by 5 p.m. EDT and moving to the northeast parallel to the coastline at 7 mph with 45 mph winds, the Miami-based hurricane center said.