A B757 Captain exercised his command authority to deviate around weather during a NYC departure because ATC told him to standby when the weather encounter was becoming imminent. ATC complained that the pilot turned before talking.

Narrative

While being vectored by New York Departure Control in a modified B757; we found ourselves within a few miles of a weather buildup; since we were still trying to familiarize ourselves with the RADAR. We asked New York Departure Control for a slight deviation around the weather; and were told to 'stand by.' I assumed the Controller was coordinating with another Controller; so I turned to avoid the weather. The Controller then approved our request and said; 'I see you're turning already.' I responded; 'I'm exercising Captain's emergency authority;' to which he said; 'you have to tell me that;' to which we didn't respond. I guess I could have told the Controller I was deviating before I turned; but I was taken aback; when he told us to stand by. That's not something you typically hear from Departure Control. I also felt it was pointless to say anything; because he was probably not listening to us. We deviated approximately 3 miles; and did not appear to cause any loss of aircraft separation.