The wireless carriers could ping/text all their customers if they wanted, and count the no-replies as missing. I think we can assume 95% of adults there have a cell.
It’s just so eerie. It was Friday, during the day. I see very few people. Just those in cars, who have no idea what is about to hit them, and very few cars on the road, but many cars swept away. There had to be tens of thousands of people close to those shores.