Songwriters have idealized New York in spring and autumn for a reason—the city is most beautiful then. If you visit April-June, you'll find generally comfortable humidity, though July and August can at times be uncomfortably hot and humid. Temperatures in April range from a low of 36 F/3 C to a high of 54 F/12 C. By June, expect daytime highs of 75 F/24 C and cool nights of 56 F/12 C.
In September and October, the clear days will be comfortable in the 60-70 F/15-21 C range, with nights demanding a warm jacket or sweater. Winter can be cold and bitter in New York, and the damp wind cuts to the bone. But New York is magical and quiet after a heavy snow (until it all turns to dirty slush). In general, extremes of temperature and humidity can make winter and summer the least dependable times to visit.