AN A319 DECLARED AN EMER FOR TSTMS IN ORDER TO MAINTAIN A TRACK AROUND WX WHILE DEVIATING OFF OF THE FMS ARRIVAL.

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ON ARR TO ZZZ DECLARED AN EMER DUE WX AND ATC VECTORS. EXTENSIVE WX CELL BUILD-UPS WITH IMBEDDED CELLS. WE WERE ON THE ARR WITH AUTH TO DEVIATE TO THE S OF COURSE FOR WX THEN TO REJOIN THE ARR. HAD PLANNED FOR THE POSTED XING RESTR. ATC RESTR OUR SPD TO 250 KTS WHICH LIMITS OUR ABILITY TO DSND. WE WERE GIVEN A FREQ CHANGE AND CHKED IN WITH THE ADVISORY WE WERE DEVIATING TO AVOID WX AND REJOIN THE ARR. ATC CLRED US DIRECT WHEN ABLE AND TO CROSS 55 NM FROM ZZZ AT FL190. WHILE BTWN 2 LARGE CELLS ATC ASKED IF WE WERE GOING TO MAKE THE XING RESTR. WE WERE TRAVELING AT R ANGLES TO THE VOR AND MILEAGE WAS CHANGING SLOWLY. OUR RESPONSE WAS 'IT'S GOING TO BE PRETTY CLOSE.' ATC STATED HE NEEDED 'A YES OR NO ANSWER.' AT THAT POINT THE WORKLOAD WAS EXTREMELY HIGH AND I DECLARED AN EMER AND ADVISED WE COULD NOT TAKE A TURN AND WOULD NEED TO PROCEED STRAIGHT AHEAD. ATC WANTED US TO TURN DIRECTLY TOWARDS ZZZ VOR. THAT WOULD HAVE REQUIRED A PATH THROUGH A RADAR RETURN THAT WAS DISPLAYING ALL LEVELS OF RETURN POSSIBLE. THERE WAS A LARGE RAIN OR HAIL SHAFT UNDER THE CELL AND VIRGA PLUS RAIN OF UNKNOWN LEVELS SURROUNDING THE SHAFT. AS WE WENT A SHORT DISTANCE FURTHER E WE ADVISED ATC WE COULD TURN TOWARDS ZZZ. I THINK HIS RESPONSE WAS 'ROGER.' SINCE THAT WAS NOT A CLRNC WE DID NOT INITIATE A TURN. AFTER ARRIVING AT ZZZ THE FLT ATTENDANTS RECEIVED A PHONE CALL ASKING IF THEY HAD TO PREPARE THE CABIN AND IF ANY PAX REQUIRED ASSISTANCE DUE TO THE EMER. I HAD SENT DISPATCH AN ACARS MESSAGE TELLING THEM I HAD DECLARED AN EMER DUE TO WX AND VECTORS FROM ATC AND WE WERE OK. APPARENTLY THAT INFO DID NOT GET TO EVERYONE. IN HINDSIGHT: THIS SPECIFIC ACFT HAD A LONG HISTORY OF WX RADAR WRITE-UPS AND I DID NOT FULLY TRUST THAT IT WOULD CONTINUE TO OPERATE. THE AIRBUS CHANGES THE RADAR GAIN LEVELS AS FLT PROGRESSES AND COUPLED WITH CHANGING WX INTRODUCES CONFUSION. SPECIFICALLY THE EARLY A319'S HAVE AN ANOMALY WITH THE RADAR BASED ON THE UNIT INSTALLED AND IT IS NOT CLR WHICH 'BRAND' MAY BE INSTALLED. WX WAS IMPACTING BOTH ARR GATES. THE PATH/DEV I CHOSE WAS CLOSING RAPIDLY. THE BEST COURSE OF ACTION MAY HAVE BEEN TO ABANDON THOSE GATES AND DEVIATE N AND E AND JOIN ONE OF THOSE ARRS.