IMC IN VFR FLT -- LOW ALT CIVIL OP A BANNER TOW PLT BECOMES DISORIENTED IN FOG AND FLIES OVER A CROWDED BEACH AT 200 FT AGL.

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DURING BANNER TOW OPS I ENCOUNTERED MVFR CONDITIONS WHICH CAUSED ME TO PASS OVER A CROWDED BEACH AT LESS THAN THE REQUIRED 500 FT MSA AS PER FARS. HOW PROB AROSE: THE WX CONDITIONS LOCALLY ON THE S SHORE OF LONG ISLAND DETERIORATED RAPIDLY; CONDITIONS INLAND ONLY SOME 4-5 MI AWAY; REMAINED VFR FOR THE BEST PART OF THE DAY (UNTIL LATE THAT EVENING). I MONITORED ATIS; TWR; APCH AND LCL CTAF'S DURING MY BANNER OP. CONTRIBUTING FACTORS: CONDITIONS AT DEP ARPT (FOK) REMAINED IFR TO MVFR ALL DAY. THUS CONDITIONS E OF ROBERT MOSES BEACH WERE LIKELY TO BE WORSE. PERCEPTION THAT 'FOLLOWING THE SHORELINE WOULD HELP' CAUSED ME TO KEEP HEADING E; FROM ROBERT MOSES BEACH MONUMENT UNTIL CONDITIONS BECAME MARGINAL IN LESS THAN A MI; 500 FT CEILING. IN PERFORMING A 180 DEG TURN TO HEAD BACK W; I PLANNED TO LOCATE THE MONUMENT; TURN INLAND; AND HEAD FOR REPUBLIC ARPT. COMPANY TFC WAS COMMUNICATING WITH ME; AND WAS ALREADY AT THE MONUMENT; ON THE SHORE SIDE; AND AT 500-600 FT AGL. WHEN I LOCATED THE MONUMENT THE LCL CONDITIONS WERE BASICALLY IFR; I ELECTED TO TURN INLAND; AS I KNEW CONDITIONS WERE VFR; OR AT LEAST BETTER; ONLY A 1/4 - 1/2 MI INLAND. DURING MY TURN INLAND I CROSSED A CROWDED BEACH AT 200 FT; JUST BELOW THE CEILING. ONCE AT THE CAPTREE BRIDGE I WAS ABLE TO CLB TO 800-1000 FT AND ENCOUNTERED 3 MI PLUS VISIBILITY. FLT ENDED SAFELY AT FRG. LOOKING BACK; I FEEL; TERMINATING THE SHORELINE PORTION OF MY FLT WOULD HAVE BEEN BETTER AT AN EARLIER TIME; DURING CONDITIONS WHICH WOULD HAVE GIVEN ME MORE VISIBILITY AND CEILING. MY RTE OF FLT FOR THAT DAY TOOK ME WBOUND FROM FOK (DEP XA00) UNDER SVFR; ALONG THE SHORE TO JONES BEACH; THEN EBOUND ALONG THE COAST AT 300 FT AGL; AS PER NORMAL BANNER OPS; BACK TO FOK. DURING THE WBOUND PORTION; UP TO JONES BEACH; VISIBILITY WAS AROUND 1-3 MI; AND I WAS ABLE TO MAINTAIN 500 FT AGL. THE SUN WAS TRYING TO BREAK THROUGH A VERY THIN BUT OBSTRUCTING LAYER. THERE WAS A VERY STRONG PERCEPTION ON MY PART THAT AS USUALLY HAPPENS; THE FOG WOULD BURN OFF. THERE WERE MANY PATCHES IN THE FOG. RPTS FROM COMPANY ACFT; WELL E OF MY POS; AT JONES BEACH; FORETOLD OF DEBILITATING WX. (1 ACFT ACTUALLY HAD TO LAND ON THE BEACH LATER THAT DAY; JUST AFTER MY OCCURRENCE.) OTHER BANNER TOW ACFT WERE ALL 'TRYING' TO GET THERE AND CONTINUE THE 'JOB' AND I WAS ADMITTEDLY INFLUENCED FOR A WHILE BY THE SAME JUDGEMENT- DECISION MAKING PROCESS. THUS; IN HINDSIGHT; AT FIRST INDICATION OF MARGINAL WX; I SHALL HEAD TOWARD NEAREST KNOWN IMPROVING OR IMPROVED/BETTER WX; RATHER THAN TRY AND 'GET THROUGH;' PUTTING MYSELF IN THE SIT I FOUND MYSELF IN WITH FEW OPTIONS OUT!