Satellite images recently released show Harvey, a slow-moving tropical storm, which has brought catastrophic flooding to Texas and killed at least nine people.
It has also led to mass evacuations and paralyzed Houston, the fourth most-populous US city. Some 30,000 people were expected to seek emergency shelter as the flooding entered its fourth day.
US President Donald Trump was scheduled to arrive in Corpus Christi, near where Harvey came ashore on Friday as the most powerful hurricane to strike Texas in more than 50 years.