(Releads with downgrade)

MEXICO CITY, May 31 (Reuters) - Tropical depression Barbara, which had threatened to become the first Pacific hurricane this year, weakened off Mexico on Thursday and was downgraded from a tropical storm, forecasters said.

The U.S. National Hurricane Center in Miami said Barbara was being broken up by other weather systems but could survive to reach the southern Mexican coast around the state of Oaxaca in the next three days.

"It now seems unlikely that Barbara will become a hurricane," the center said, adding the storm's sustained winds had dropped to 35 mph (56 kph).

Earlier reports had Barbara developing into a hurricane over the weekend and barreling toward small coastal resorts like Puerto Escondido, a major surf spot.

Tropical Depression Alvin, which earlier this week reached tropical storm strength, is also lurking in the Pacific Ocean but is a long way off the coast.

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