A B737-300 PLT COMMENTS THAT ATC ALLOWED ANOTHER ACFT'S RWY 13 TKOF ROLL TO BEGIN WHILE HIS ACFT WAS XING BUT STILL PARTIALLY ON RWY 13.

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THE SAME PERSON WAS WORKING CLRNC DELIVERY; GND AND TWR. TAXI CLRNC WAS 'TAXI TO RWY 9L; CROSS RWY 13; AN ACFT IS HOLDING ON RWY 13.' I CHKED MY CHART AND TOLD THE FO; WHO HAD NEVER BEEN TO PBI; LOOKS LIKE A STRAIGHT AHEAD TAXI ON TXWY A AND WE ARE CLRED ACROSS RWY 13. 100 YARDS FROM RWY 13 I REMARKED I COULD SEE THE ACFT HOLDING ON THE RWY. THE FO ASKED GND TO CONFIRM WE WERE CLRED TO CROSS RWY 13 AND RECEIVED AN AFFIRMATIVE RESPONSE. ALL LNDG LIGHTS AND OTHER EXTERNAL LIGHTS WERE ILLUMINATED 25 YARDS FROM RWY 13. AS THE NOSEWHEEL WAS ABOUT 10 FT FROM THE HOLD SHORT LINE OF RWY 13; 10 KTS TAXI SPD; TWR CLRED THE ACFT HOLDING IN POS FOR TKOF. I IMMEDIATELY APPLIED MORE PWR AND CROSSED THE RWY. IF I HAD APPLIED BRAKES; WE WOULD HAVE STOPPED WITH THE MAJORITY OF OUR ACFT ON THE RWY. I BELIEVE WE WERE OFF THE RWY BEFORE THE OTHER ACFT BEGAN HIS TKOF ROLL. DISTANCE BTWN ACFT WAS NEVER LESS THAN 300-500 FT. I TOLD TWR WE WERE ON THE RWY WHEN HE CLRED THE OTHER ACFT FOR TKOF. HE REPLIED THAT IT WAS DIFFICULT TO TELL FROM THE TWR AND HE THOUGHT WE WERE PAST RWY 13. I WAS VERY UPSET AND MADE NO FURTHER RADIO CALLS. THE TWR IS NOT LOCATED IN A GOOD POS. TWR SHOULD EITHER HAVE TOLD US TO CALL CLR OF THE RWY; LIKE IN CAT 3 OPS OR HAVE A POINT OF REF THAT TELLS THEM WE ARE CLR. ALSO; GND RADAR MIGHT HELP. HOWEVER; THERE IS ONLY SO MUCH 1 PERSON IN THE TWR CAB CAN DO. COMPANY PROCS ARE GREAT. WE EVEN MADE AN EXTRA CALL TO CONFIRM RWY XING PERMISSION. MAKE IT FOGGY; DISTANCES A LITTLE CLOSER AND WE HAVE ANOTHER CANARY ISLANDS INCIDENT.