New York City’s summer humidity is unpleasant in so many ways: Shirts are sweaty by noon, flowers wilt, and garbage smells linger. But it’s really curly hair that suffers most.

Today at the South Street Seaport, the hair-product line John Frieda Frizz-Ease will unveil its “Frizz-O-Meter,” designed to forecast bad hair days. The 7-foot-tall contraption measures humidity and offers a prediction of the weather’s effect on hair that day with a carnival-style dial. The scale ranges from Frizz Watch (“light frizz and flyways possible”) to Frizz Emergency (“frizz is unavoidable!”). The Frizz-O-Meter is headed for a five-city tour of muggy locales, including Houston and New Orleans. Don’t want to leave the apartment to get a frizz forecast? During the month of July, both www.johnfrieda.com and www.accuweather.com provide updated frizz reports broken down by Zip code.

Luckily, on those emergency days, curly haired New Yorkers have some resources. The one-named stylist Ouidad presides over the Ouidad Salon (37 W. 57th St., 212-888-3288, www.ouidad.com), billed as the first and only salon in America “devoted exclusively to curly, frizzy hair.” She has actually trademarked her “slicing and carving” technique for cutting curly hair. Ouidad’s Tame line of products was created for frizz and fly-aways ($30 for shampoo, rinse, and gel); for children, there’s the Krly Kids Collection ($30 for shampoo, conditioner, and gel).

Christo, a former student of Ouidad, opened his own curly-hair salon in 2002. For humid days, his product line, Curlisto Systems, offers Structura Spray ($12), and the “setting and bodifying agents” Control 1 and Control 2 ($24 and $28, respectively). The most intense product is Control Glue, which comes in an Elmers-esque bottle and claims to provide “extreme long-lasting hold” for frizzy dos. Christo favors curly heads at his salon, too: He charges $50 for styling curly hair – and $70 for straight. (Christo Fifth Avenue, 574 Fifth Ave., fifth floor, 212-997-8800).

The SoHo salon Devachan also caters to curly heads, but with a downtown spin. Owner Lorraine Massey maintains that frizz comes from “detergent” shampoos, so her DevaCurl product line adds moisture rather than rinsing it out (Devachan Salon & Departure Lounge, 560 Broadway, 212-274-8686).

For de-frizzing on a drugstore budget, Aussie offers 12-Hour Humidity Spray, Calm that Frizz! Styling Spray, and Tizz No Frizz Gel ($3.50-$5). L’Oreal Vive Smooth-Intense Anti-Frizz Cream adds moisture ($6). And John Frieda Frizz-Ease is still the Coca-Cola of frizz-fighting products. The line now includes 19 products, from Smooth Start Shampoo to 100% Shine Glossing Spray ($5-$10).

If all else fails, banish frizz-causing curls altogether: Le Salon Chinois offers a Japanese hair-straightening technique that devotees swear eliminates curls for six to 10 months – no blow-drying required. The process can take up to six hours, but treated hair “will never be curly again.” (Le Salon Chinois, 44 W. 55th St., 212-956-1200, $120/hour, www.lesalonchinois.com)