“So far, we’ve received almost 700 total evacuees, with 10 additional full buses waiting to check in as we speak,” Mayor Ron Nirenberg said. “We expect that number to climb as coastal cities continue to experience significant rainfall and high winds.”

Hundreds of relief workers have come from around the state to help man the shelters, and medical facilities in San Antonio have already received many patients from coastal areas, the Bexar county judge, Nelson Wolff, said.

“Some 190 patients have been moved up to the Bexar County area to be able to be transferred to a safer hospital environment,” Mr. Wolff said. — STACI SEMRAD in San Antonio

It’s not just the wind, it’s the water.

Forecasters are saying this is the first major hurricane to hit the United States in 12 years. That’s the kind of statement that is accurate, but galling for those who went through storms like Sandy in the Northeast in 2012, or Ike, which was so destructive to the Texas Gulf Coast in 2008.

The distinction is this: to be called a major storm, a hurricane must be Category 3 or higher on the Saffer-Simpson hurricane wind scale, which means winds of 111 to 129 miles an hour. Those winds can bring “devastating” damage, stripping off roof decking and bringing down many trees. Ike was a Category 2, though it pushed a monster storm surge. Sandy had become what is known as a post-tropical storm before it made landfall. Late Friday, Hurricane Harvey became a Category 4 storm with sustained winds of 130 miles per hour.

The lesson is that it is not just wind that makes a storm dangerous. Storm surge, the water that a hurricane pushes ahead of it, can be tremendously destructive. Much more harm was done to New Orleans during Katrina because of the surge — which overwhelmed the area’s faulty levees — than the wind.

Beyond surge is the rainwater. Tropical Storm Allison was not even at hurricane strength when it came to Houston in 2001, but it sat over the city in much the way that Harvey is expected to do. Southeast Texas suffered nearly $5 billion in damage from the storm, with 22 deaths. — JOHN SCHWARTZ

Mexican authorities issue safety warnings.

Mexico, through its National Weather System, issued a statement on Friday morning forecasting “intense storms” in the northern states of Tamaulipas, Nuevo León and Coahuila near the Gulf. The Mexican authorities strongly recommended that people in the region take safety precautions ahead of heavy rain, wind and waves. — PAULINA VILLEGAS in Mexico City