Carrying an umbrella in this city is perilous business: Too big, and you’re dodging pedestrians on the sidewalk; too cheap, and it blows apart at first gust; too dark, and it may be swallowed forever by some barroom floor. Davek’s new pocket-size umbrella ($49 at Ame Ame, 318 E. 9th St., nr. Second Ave.; 646-867-2342) is the urban rain warrior’s best defense. The brightly hued protectors measure about seven inches when closed, but span a generous 34 inches when open. And unlike flimsy aluminum numbers you buy from the deli (and inevitably toss), this one’s rustproof steel ribs are reinforced with fiberglass ligaments that won’t flip inside-out during an April downpour.