B737-800 CREW HAD CONFUSION ON JUST WHAT APCH THEY WERE CLRED FOR AT MDLR.

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APCHING LA ROMANA; DOMINICAN REPUBLIC (MDLR); HAD PRE-BRIEFED A VOR TEARDROP RWY 11 APCH WITH PLAN TO BREAK OFF AND SHOOT STRAIGHT IN VISUAL UPON SIGHTING FIELD. HAD DISCUSSED SETTING UP FMS GLIDE PATH NON- PRECISION APCH GUIDANCE FOR PRACTICE AND TO BACK UP VISUAL GUIDANCE TO FIELD. APCHING ARPT; RADAR SHOWED STRONG RETURNS AND TWRING CUMULUS CLOUDS WERE VISIBLE IN AREA. ON LET DOWN; VISIBILITY BELOW CLOUD BASES (2500-3000 FT MSL) WAS GENERALLY GOOD; WITH LESS VISIBILITY IN THE DISTANCE WHERE RAIN WAS VISIBLE. COORDINATED WITH ARR/APCH TO VECTOR ACROSS FINAL TO S OF ARPT OVER OCEAN TO HOLD AND LOOK AT WX SIT. AT THIS TIME; ARPT RPTED 'TSTM' OVERHEAD; HVY RAIN. RADAR SHOWED HVY RETURNS. S OF FIELD WAS DAYLIGHT VMC; NO CEILING SCATTERED CLOUDS 3000 FT MSL; UNLIMITED VISIBILITY. PUBLISHED APCH HAD NO FAF BUT WAS A BASE TURN FROM OVERHEAD VOR AT FIELD TO FINAL STRAIGHT IN. WE WERE HOLDING S OF EXTENSION OF FINAL; OBSERVING WX AND GETTING RPTS. AFTER 10 MINS TWR RPTED RAIN OFF FIELD; 2500 FT CEILING; 7 KM VISIBILITY WINDS CALM. WE COULD SEE AREA OF FIELD FROM OUR POS JUST BELOW BASE OF CLOUDS; ALTHOUGH RAIN BTWN OUR POS AND THE FIELD MADE DETERMINATION OF VISIBILITY DIFFICULT. REQUESTED DIRECT TO 11 DME ON VOR FINAL TO LINE UP AND ACQUIRE RWY. SOME LANGUAGE DIFFICULTY WITH CTLR AS FAR AS ACTUAL CLRNC. WE MADE IT CLR THAT WE PLANNED TO PROCEED DIRECT TO THIS FIX AND COME STRAIGHT-IN ON FINAL TO AVOID WX N OF FIELD. WE WERE IN RADAR CONTACT ON VECTORS AT 3000 FT MSL. MSA FOR OUR POS WAS 2000 FT MSL; BUT CTLR WOULD NOT GIVE US LOWER THAN 3000 FT TILL ESTABLISHED ON FINAL. I WAS RELUCTANT TO ACCEPT VISUAL BECAUSE OF RAIN; EVEN THOUGH FIELD WAS BEING CALLED VFR. CTLR CLRED US TO THE FIX AND FOR THE APCH. WE DID NOT CALL THE FIELD RIGHT AWAY; WHICH IN RETROSPECT RAISES THE QUESTION; WHAT KIND OF APCH WERE WE ACTUALLY CLRED FOR? HE NEVER ACTUALLY SAID 'CLRED VISUAL APCH;' HE JUST SAID 'CLRED APCH' AND WE WERE SO BUSY EVALUATING OUR MARGINAL VISIBILITY CONDITIONS; AND TRYING NOT TO LOSE TRACK OF OUR POS VISUALLY AND BACKING THAT UP WITH THE VOR FINAL AND GLIDE PATH IN THE FMC THAT WE DID NOT THINK TO QUESTION IT. THERE IS NO PUBLISHED STRAIGHT IN APCH IN OUR COMMERCIAL CHART PROVIDER FOR THIS RWY; AND YET; AS WE LINED UP ON FINAL; THE RAIN CAUSED US TO RELY HEAVILY ON THE VOR/FMC GUIDANCE FOR THE FINAL SECTION OF THE VOR BASE THAT LINES UP WITH THE LNDG RWY. I CALLED RWY IN SIGHT THROUGH THE RAIN; AND ENCOUNTERED GENERAL VMC (NO RAIN). ON ABOUT 4 MI FINAL; TWR CLRED US TO LAND. MARGINAL VFR CONDITIONS EXISTED WHILE IN THE RAIN FOR A COUPLE OF MI ON FINAL. USED THE VOR FINAL AND PUBLISHED MINIMUMS TO BACK OURSELVES UP; BUT WE COULD NOT ACTUALLY HAVE BEEN SHOOTING THAT APCH BECAUSE WE INTERCEPTED IT INSIDE THE IAF; WITH NO PUBLISHED FAF. MORAL OF THE STORY; SHOOT THE WHOLE APCH IF WX IS QUESTIONABLE; AND MAKE CERTAIN WHAT THE CTLRS HAVE CLRED YOU TO DO (COMPLICATED BY LANGUAGE DIFFICULTIES). LNDG UNEVENTFUL.