They claim the aggressive act was US forces conducting training excercises in South Korea. THis is something that I participated in for 11 months and amounts to precisely dick. This is not new or aggressive behavior, it's merely the US training with their ALLY South Korea.
In particular, the threat NK made was in direct response to sanctions imposed by the US and CHINA(their own ALLY) for reckless behavior, threatening global stability, and general asshattery. Oddly enough, NK's government is near collapse and a limited conflict may actually temporarily save them. Threatening such action is likely to garner some form of financial appeasement or increase the odds of a limited combat engagement.
As for the intended target of a nuclear attack. Washington is completely out as is New York. The range of their systems is barely enough to cross the pacific and the longer it stays in the air the more opportunity to have it shot down or malfunction. They could surprise Hawaii but it would not serve them well as it would irradiate their own waters that they rely on for fishing. LA or Washington State are potential targets but also unlikely due to well placed assets that would intercept with the 45 minute warning. I believe if they WERE to launch an attack it would be a limited short range, low yield tactical strike on one of the two main US bases in South Korea. It would be a bold attack and would disorganize a counter-strike buying themselves enough time to negotiate terms for a cease fire before all hell rained down on them.
After 7 years in the military I would rate the likelihood of a nuclear attack from them somewhere around 2%. It's not impossible, but I won't worry unless I win the lottery and the Chicago Cubs win the World Series in the same year.
BTW Misco, I am also in NYC and we would indeed be "boned" as even if it didn't hit us, gridlock from panicked hipsters trying to leave the city would.