* Hurricane expected to weaken on Friday
* No oil installations threatened (Updates with closure of port Lazaro Cardenas)
MEXICO CITY, July 20 (Reuters) - Hurricane Dora strengthened to a Category 3 storm in the Pacific Ocean off Mexico on Wednesday and could still intensify further, the U.S. National Hurricane Center said.
Dora, the fourth named storm of the Pacific hurricane season, churned 220 miles (350 km) south of the western port city of Lazaro Cardenas with winds of 115 miles per hour (185 kph), the Miami-based hurricane center said.
Lazaro Cardenas, a major shipping port, was closed as waves and strong winds lashed the coastline. The rest of Mexico's main Pacific ports were open on Wednesday afternoon.
Mexico has no major oil installations on its Pacific coast, but sugar- and coffee-growing cropland in southern states could be soaked. A tropical storm watch is in effect for the area from Lazaro Cardenas to Cabo Corrientes further northwest.
The hurricane, a Category 3 on the five-step Saffir-Simpson scale, is shadowing Mexico's Pacific coastline.
"The center of Dora is expected to move nearly parallel to the coast of southwestern Mexico," the center said.
Dora could become a Category 4 hurricane on Thursday, before probably starting to weaken on Friday, the center said.
Tropical storm conditions along the coast could cause life-threatening waves and rip tides, the center said.
(Reporting by Rachel Uranga; Editing by Sandra Maler)
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