Thunder

The term tr. “pestilence” is Heb. דֶּ֫בֶר, H1822, the same term that is used for the fifth plague q.v. (Exod 9:1-4. The “B” opposite the second line rendered “plague” is Heb. רֶ֫שֶׁף, H8404, which is cognate to Ugaritic ršp, Canaanite, ršp, prob. read rašap, on the basis of a divine name and the personal name Abi-Rasap found in the Mari letters. This word meaning “pestilence,” “plague,” was used as the name of a pagan plague-demon throughout Western Asia among the various Semites.

International Standard Bible Encyclopedia (1915)

Lightning and thunder are indications of the power of Yahweh and His might. "The thunder of his power who can understand?" (Job 26:14); "The God of glory thundereth" (Ps 29:3). Yahweh also confused the Philistines with thunder (1Sa 7:10), and His foes were "visited of Yahweh of hosts with thunder" (Isa 29:6). Thunder was regarded as the voice of Yahweh: "God thundereth with the voice of his excellency" (Job 37:4), and God spoke to Jesus in the thunder (bronte, Joh 12:29).