Q. When an author speaks of a particularly difficult experience with the following metaphor, how should it be styled: “category 5 storm,” “category five storm,” “Category 5 storm,” “Category Five storm”?
A. Many proper nouns and adjectives lose their capital letters when they are demoted from literal to figurative use. So a French restaurant in Detroit might serve french fries (not literally from France). Or Thomas More’s Utopia might inspire utopian dreams. But for maximum impact, some metaphors are best expressed in literal terms. If you’re going to compare something to a numbered category in the Saffir-Simpson Hurricane Wind Scale, it will be more effective if you parrot official style and retain the capital C (and the numeral 5).