The storm was expected to bring heavy rains and flooding to Texas and Louisiana late this week and into the weekend. There is some potential that Harvey will slow significantly or even stall once inland, resulting in a prolonged stretch of heavy rains. Overpeck said there is a small possibility that Harvey becomes a weak hurricane, but the greatest danger it poses is rain.
High surf could produce major flooding, especially along coastal areas of Texas anywhere from Corpus Christi to Houston.
Hurricane, tropical storm and storm surge watches have been issued for parts of Texas.
In its 1 p.m. ET advisory, the weather service said Harvey is located off Mexico's Yucatan Peninsula, 535 miles south-southwest of Port O'Connor, Texas with maximum sustained winds near 35 mph, and was almost stationary. There are no changes in status of with any of the watches with the latest update from the National Hurricane Center.
Meteorologists forecast Harvey to possibly become a hurricane by late Friday before it makes landfall - that could be along the US coast. In fact, Tropical Storm and Hurricane Watches have been posted for the southeast Texas coast.
"Upper-level winds are not conducive for development of this system while it moves northwestward over the central Atlantic at 10 to 15 miles per hour, forecaster Dan Brown said in the 2 a.m.tropical weather outlook". Less rain is expected in south, central and northeast Texas, and the lower Mississippi Valley.
The National Hurricane Center said areas far inland, including Houston, the fourth-largest city in the USA, could experience flooding from Harvey's vast amounts of potential rainfall.
Phil Klotzbach from Colorado State University who is a hurricane research scientist said that the longest duration streak without landfall in Texas is 11 years - 1855 to 1865.
It was delayed by a day or so, but that heavy rain event is coming this afternoon, the National Weather Service says.