For 12 years, National Geographic photographer Carsten Peter chased tornadoes alongside researcher Tim Samaras and his team. Samaras, his son Paul, and Carl Young died Friday, May 31, chasing a tornado that touched down near El Reno, Oklahoma.
Many of Peter's photos appeared in the pages of National Geographic magazine, but others were not published. We asked Peter to share some of these unpublished photos—and talk about his memories of Samaras.
"For me, it's really tragic to lose all three friends at once. This is unbelievable," he said. "You can imagine, if you work together for 12 years, we have incredible memories together. Now I feel quite alone with these memories."
In the photo above, Young (at left) and Tim try to estimate the size of a massive thunderstorm bearing down on Piedmont, Oklahoma, in 2012.
"There were tight situations, especially in this storm, because there was huge hail," said Peter. But he felt safe when chasing storms with Tim, he added.
—Jane J. Lee and Melody Kramer