Sinaloa is the country's top grower of corn, Mexico's staple grain, as well as a major producer of tomatoes and other fruits that figure prominently in the country's agricultural exports to the United States.
The NHC's latest advisory placed Pamela about 85 miles north-northeast of the major Sinaloa beach resort of Mazatlan and said the tropical storm was packing maximum sustained winds of 65 miles per hour.
Additional "rapid weakening" is forecast as the centre of Pamela moves farther inland, said the NHC.
Through Thursday, the storm is forecast to produce 4 to 8 inches of rain, with isolated maximum totals of 12 inches, across Sinaloa and western Durango state and northern Nayarit state, which could trigger significant and life-threatening flash flooding and mudslides.
The NHC said that across portions of central Texas and south-eastern Oklahoma 3 to 6 inches of rain, with isolated maximum totals of 8 inches, were expected, which could cause considerable flash and urban flooding.
In preparation of the heavy rains and winds, Mexican authorities said that 40 temporary shelters were opened in Sinaloa.