"We have a tropical storm with a very clear possibility of reaching hurricane strength," National Water Commission chief David Korenfeld told reporters estimating an 80 percent chance it will reach hurricane force.
"In the next 72 hours on the Mexican Pacific coast, we will be seeing very heavy rains, torrential rains" of 150 millimetres and more, Korenfeld warned.
He voiced concern about the rain hitting already waterlogged areas that in many cases are still recovering from the last series of storms.
It boasted sustained winds of 110 kilometres per hour as it moved north-northwestward at 10 kilometres per hour.
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Mexico's national weather service said Raymond was already dumping heavy rains and sparking waves two to three meters high.
Authorities in Guerrero issued alerts for the centre and south of the state.
They also kept a close watch on four reservoirs in this arid region that have already reached maximum capacity.
In mid-September, Tropical Storm Manuel made landfall in Guerrero, while another weather system, Ingrid, slammed almost simultaneously into the opposite coast.
The two storms claimed 157 lives and left 1.7 million people homeless.
Their effects were felt across two thirds of the country, but hardest hit was Guerrero, where landslides partially buried a mountain community and 101 of the deaths were recorded.
The unusual double storm blast occurred during a holiday weekend leaving thousands of tourists stranded in Acapulco when airports and highways were closed.