At 9 p.m. (local time) on Thursday night, the storm was located 490 km southeast of Corpus Christi, and moving toward the north-northwest at 17 km/h, according to the latest NHC advisory.
Harvey, now a Category 1 storm with maximum sustained winds of 140 km/h, is forecast to make landfall on the middle Texas coast late Friday or early Saturday as a major hurricane (Category 3, 4 or 5).
The advisory expanded the hurricane warning area, which now extends from Port Mansfield northeastward to Sargent, an area that is home to more than 1.4 million people.
A tropical storm warning has been issued for a larger area populated by roughly 12 million people that includes Houston, the fourth-largest city in the US.
Heavy rains could also affect other parts of southern, central and eastern Texas and neighbouring Louisiana.
"Rainfall from Harvey may cause devastating and life-threatening flooding," the NHC said.
Texas Governor Greg Abbott has already declared a state of emergency for 30 counties that lie in the storm's path.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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