MLG FLT DEVIATED FROM CLRED COURSE.

Narrative

FLT EWR-DCA AT CRUISE ALT WITH CLRNC TO DSND; CLRED TO FLY V378 (VOR 245 DEG RADIAL) BAL; DCA. THIS WAS NOT ORIGINAL RTE. AT BAL VOR V378 APPEARED TO FLY INTO CONVECTIVE ACTIVITY. A SLIGHT DEV TO THE L OF COURSE WAS TAKEN TO AVOID RADAR DEPICTION OF HVY WX. MODERATE TURB AND RAIN BUFFETED THE ACFT AND THE DSCNT WAS INITIATED. SHORTLY THEREAFTER; A VERY ANNOYED CENTER CTLR INFORMED ME THAT I WAS 10 MI L OF THE AIRWAY IN ANOTHER (WASHINGTON) SECTOR'S AIRSPACE. I THEN REALIZED THAT; WITH ALL THE DISTRS OF DSNDING THROUGH WX; TURB; AND AVOIDING TSTMS; I HAD NEGLECTED TO TELL THE CTLR WHAT I WAS DOING AND WHY. I SHOULD HAVE INFORMED THE CENTER OF WHAT WAS TRANSPIRING IMMEDIATELY! HE HAD A RIGHT TO KNOW AND TO BE ANNOYED! I RECEIVED QUITE A LECTURE ABOUT HOW IMPORTANT IT IS TO ADHERE TO THE AIRWAY AND HOW CLOSE THE SECTOR AIRSPACE BOUNDARY WAS. I FELT ABOUT 2 INCHES HIGH. IT WAS SOUND JUDGEMENT TO AVOID THE HVY WX BUT FAILURE TO INFORM THE CTLR OF MY COURSE OF ACTION IN A MORE TIMELY MANNER COULD HAVE CAUSED A PROBLEM AT LEAST AS SERIOUS AS A TSTM. UPON ARR AT MY DEST; I PHONED BOTH THE NEW YORK SECTOR AND THE ADJACENT WASHINGTON SECTOR AND WAS ASSURED THAT NO 'INCIDENT' HAD OCCURRED. I TOOK THIS OPPORTUNITY TO ASSURE THOSE INVOLVED THAT I REALIZED THE SITUATION I HAD PLACED THE CTLR IN AND TO REASSURE MYSELF THAT A MORE SERIOUS SITUATION DID NOT OCCUR. MORAL: IN ATC ENVIRONMENT; COMMUNICATE!