FLC OF AN MD88 CHANGED HDG AND DSNDED TO AVOID WX CELLS SHOWN ON THEIR ACFT RADAR WX SCOPE WITHOUT CLRNC FROM CTR DUE TO CONGESTED FREQ.

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SEVERAL MI N OF MLB; CAPT (PNF) REQUESTED DEVS L OR R OF COURSE. ATC INQUIRED AS TO WHY; AS OTHER ACFT HAD FLOWN THE TRACK WE WERE ON. CAPT RESPONDED THAT WE WERE PAINTING WX AND NEEDED TO DEVIATE. CTR RESPONDED WITH FREQ CHANGE; TELLING US TO MAKE OUR REQUEST ON THE NEXT FREQ. ON INITIAL CALL TO NEW FREQ; CAPT REQUESTED DEV 20 DEGS L FOR WX. ATC RESPONDED; DEV APPROVED; DSND FROM 10000 FT TO 6000 FT. AS WE BEGAN THE TURN IT WAS OBVIOUS THAT THE LEVEL 3-6 CELL WAS STILL DIRECTLY AHEAD. CAPT ATTEMPTED TO TELL ATC WE NEEDED FURTHER L; BUT FREQ WAS CONGESTED WITH NUMEROUS CALLS. THE CAPT THEN TOOK CTL OF THE AUTOPLT AND TURNED THE ACFT TO A SAFE HDG AWAY FROM THE WX. WHEN THE RADIO CLRED THE CAPT TOLD ATC OF OUR DEV AND OUR NEW HDG 090 DEGS. ATC RESPONDED; MAINTAIN 10000 FT FOR TFC DIRECTLY AHEAD. I RESPONDED BY DISENGAGING THE AUTOPLT AND CLBING FROM 9700 FT TO 10000 FT. FROM THIS POINT; ATC GAVE US VECTORS AROUND THE STORM. MY FEELING IS RADIO FREQ CONGESTION PREVENTED CLR 2-WAY COM BTWN OUR ACFT AND ATC. THIS MADE IT DIFFICULT (OR IMPOSSIBLE) FOR THE CAPT TO COMMUNICATE OUR SAFETY NEEDS TO ATC.