I don’t think that saying there is a physical explanation means that it cannot be a warning from God. In the over 4,000 years of history that scripture covers, giving us how God operates in our world it reports many miracles, and often something physical was required for the miracle or to precede it. Mud was used for a blind man, a woman touched Jesus’ garment, and Moses used physical happenings to free the Hebrews. God works in the physical happenings of our world, too.