Hurricane Sandra, the strongest storm on record this late in the Pacific hurricane season, surged to Category 4 off the coast of Mexico on Thursday.

Moving northwest towards Mexico, the storm has rapidly grown since it formed Tuesday -- reaching the second-highest category on the Saffir-Simpson scale -- but forecasters expect it to weaken before hitting land.

At 0900 GMT, Sandra was packing winds of 230 kilometers (140 miles) an hour, with gusts rising to 280 kilometers, according to Mexico's national weather service, the SMN.

Currently moving at 19 kilometers per hour, the storm is 470 kilometers southwest of Socorro Island, off Mexico's west coast, and 810 kilometers from Jalisco state.

The National Hurricane Center in Miami has advised residents of Mexico's west coast to monitor Sandra's progress, but said it was forecast to start losing strength by Thursday night.

The SMN expects it to make landfall as a tropical storm at the end of the week, bringing heavy rain and waves of up to 2.5 meters to the south of Baja California.

The Pacific hurricane season, which runs from May to the end of November, has produced 18 named storms, 12 of which became hurricanes.