The centre of the storm by Wednesday afternoon had appeared to move inland in southeast Texas, but Arthur's impacts were set to be felt well beyond, according to the National Hurricane Center in Miami. Maximum sustained winds were around 75km/h, and the storm was expected to lose strength as it moved further over land.
Officials urged millions of people along the Gulf Coast to take the storm seriously amid warnings that the storm could dump dangerous amounts of rain in some areas. In Louisiana and Mississippi, some communities set up locations for residents to collect sandbags and cleared debris from drainage systems.
Flooding was likely through Friday over parts of Texas, Louisiana, Mississippi, Alabama, Georgia and the Florida Panhandle, the hurricane centre said.
After being inundated with heavy rain earlier this week, parts of central and south Mississippi braced for a second wave of potential flooding.
The tropical storm is expected to produce rainfall totals of up to 25cm, with isolated higher totals near 50cm.
The combination of storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline.
Swells generated by Arthur are likely to cause life-threatening surf and rip-current conditions along the northwestern Gulf Coast for the next couple of days, forecasters said. Tornadoes were possible through Thursday.
Arthur formed as some areas along the Texas coast had already been drenched by bands of heavy storms that caused flooding and high waters.
Near Houston, a 15-year-old drowned on Tuesday after entering the water of a retention pond while playing near a construction zone, according to the Montgomery County Sheriff's Office.
