There are two instances of variation in grammatical number in this verse. First of all, as discussed nearby under 3 Nephi 8:12, Oliver Cowdery initially wrote tempest here in 3 Nephi 8:17 rather than the correct tempests; his correction to the plural was virtually immediate. The second change was in the 1874 RLDS edition, where thunderings was replaced by thundering. The 1908 RLDS edition restored the original plural. Note that all the nearest conjoined nouns are in the plural (“because of the tempests and the thunderings and the lightnings”). The critical text will therefore maintain the plural thunderings in this passage.
Summary: Maintain in 3 Nephi 8:17 the plurals tempests and thunderings, the reading of the earliest textual sources.