FLC OF A320 HAS WX BELOW MINIMUMS AT DEST AND DIVERTS TO FINAL DEST INSTEAD OF FLT PLANNED ALTERNATE. DISPATCH DOES NOT KNOW WHERE THEY ARE.

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I WAS PIC ON AN AIRBUS A320 ENRTE FROM NEWARK ARPT TO MYRTLE BEACH; SC. WX WAS SOLID IMC AND SCATTERED TSTMS. MY ALTERNATE FOR MYRTLE BEACH WAS RALEIGH DURHAM; NC. AS WE GOT CLOSER TO MYRTLE BEACH WX THERE DROPPED TO 1/4 MI VISIBILITY AND 100 FT CEILING. I CONTACTED MYRTLE BEACH OPS AND ADVISED THEM I WOULD BE DIVERTING TO ST PETERSBURG; FL; SINCE THAT WAS OUR FINAL DEST. THEY ADVISED ME THIS WAS A GOOD IDEA AND TOLD ME THAT MY FLT OPS WERE BEING ADVISED OF THIS DEV. I CALCULATED FUEL AND WX CONDITIONS AND PROCEEDED TO ST PETERSBURG WITHOUT MISHAP. AFTER LNDG I CALLED DISPATCH AND THEY ADVISED ME THAT THEY HAD NO IDEA WHERE WE WERE AND ALMOST DECLARED THE ACFT AS MISSING. THE FAA HAPPENED TO BE AT DISPATCH OPS THIS DAY AND OBSERVED THE WHOLE MISHAP. MY PERSONAL PHYSICAL CONDITION AT THE TIME WAS POOR. I WAS SUFFERING FROM THE FLU AND WAS VERY FATIGUED. MY MISTAKE IN ALL THIS WAS I DID NOT CALL DISPATCH ON COMMERCIAL RADIO AND NOTIFY THEM OF OUR DEV. I DON'T KNOW IF ANY ACTION WILL BE TAKEN AGAINST ME BUT I FIGURED I SHOULD SEND THIS NASA FORM IN.