CREW ELECTS TO REJECT THE TAKEOFF AFTER ROTATING DUE TO WINDSHEAR ENCOUNTER THAT CAUSES ACFT TO SETTLE BACK ON THE RWY.

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CLRED FOR TKOF ON RWY 3 APPROX XA50. FO WAS AT THE CTLS. CURRENT METAR (NEARLY 1 HR OLD) AS FOLLOWS: DATE AND TIME 050/06KT 10 SM SCT110 19/M06 A3000. LIGHT WIND WAS CONFIRMED BY OBSERVATION OF WINDSOCK AND FLAGS. REVIEW OF PERFORMANCE CHARTS SHOWED COMFORTABLE MARGINS FOR ACCELERATION/STOP AND ACCELERATION/GO. BROKEN CLOUDS AND VIRGA WERE NOTED TO THE S; SCATTERED TO BROKEN CLOUDS WERE OBSERVED TO THE N. RWY WAS DRY AND CLEAN. ROTATION SPD WAS INCREASED BY 6 KTS OVER THAT REQUIRED FOR OUR TKOF WT TO ASSURE CLEAN UNSTICK. MAX PWR WAS SET BEFORE BRAKE RELEASE. ACCELERATION WAS NORMAL UNTIL AFTER 80 KT STATUS CHK AND CALLOUT. MOMENTARY HESITATION OF IAS INCREASE WAS NOTED AT APPROX 87 KTS; FOLLOWED BY RESUMPTION OF NORMAL ACCELERATION. NORMAL ROTATION TO TOGA V-BAR PITCH ATTITUDE RESULTED IN LIFT-OFF; BUT THE ACFT IMMEDIATELY BEGAN TO SETTLE. IAS WAS DECREASING RAPIDLY IN SPITE OF SUBJECTIVE FEEL OF NORMAL ACCELERATION. SUBJECTIVELY; GND SPD WAS INCREASING RAPIDLY. MAIN WHEELS CONTACTED THE RWY 2-3 SECONDS AFTER LIFT-OFF. FO CORRECTED FOR A SLIGHT WEATHERVANE YAW ON LIFT-OFF AND MAINTAINED TKOF PITCH ATTITUDE. WHEN THE MAINS TOUCHED DOWN; I TOOK THE CTLS AND APPLIED FULL REVERSE AND MODERATE BRAKING (TO AVOID WHEEL LOCKUP). APPROX 2500 FT OF RWY REMAINED. IAS WAS LESS THAN 100 KTS; GND SPD (SUBJECTIVELY) WAS AT LEAST 120 KTS. UPON REACHING THE END OF THE PAVEMENT; I STEERED 10 DEG L TO AVOID THE LOC ANTENNA BERM; CONTINUED FULL REVERSE; AND APPLIED MAX BRAKING ON SANDY SOIL. FO ASSISTED WITH BRAKING AND EXECUTED THE EMER SHUTDOWN PROC BEFORE THE ACFT CAME TO REST. THE ACFT STOPPED APPROX 500-600 FT PAST THE END OF THE RWY. AFTER ASSURING THAT EMER EGRESS WAS NOT REQUIRED; I EXITED THE ACFT AND FOUND ALL LNDG GEAR INTACT AND NO VISIBLE DAMAGE. BOTH MAINS DEFLATED WITHIN A FEW MINS WHEN THE FUSE PLUGS ACTIVATED FROM THE HEAT GENERATED BY THE MAX BRAKING EFFORT. I NOTED A STRONG; STEADY WIND; ESTIMATED TO BE IN EXCESS OF 20 KTS; COMING FROM THE DIRECTION OF THE RWY. THE NEW METAR AT XA54 SHOWS 340 DEGS 12 KTS GUSTING 23 KTS. RWY WAS CHANGED TO RWY 21 WHILE WE WERE WAITING FOR SVC VEHICLES TO ARRIVE. THIS EVENT IS THE RESULT OF A STRONG NEGATIVE WINDSHEAR AT ROTATION. MY DECISION TO ABORT WAS PROMPTED BY A FLASHBACK TO A SIMULATOR SCENARIO (CE560) A FEW YRS AGO. IF I HAD TO DO IT AGAIN; I WOULD DISCONTINUE THE TKOF AT THE POINT WHERE THE IAS HESITATED MOMENTARILY. OUR TRAINING DISCOURAGES ABORTING AFTER 80 KTS EXCEPT FOR FIRE; ENG FAILURE OR DIRECTIONAL CTL. THE FO AND I WERE PRIMED TO CONTINUE IN THE ABSENCE OF AN ABNORMAL INDICATION PRIOR TO 80 KTS. IN THIS SITUATION; I DO NOT BELIEVE THE ACFT COULD HAVE REMAINED AIRBORNE AND CLBED TO AVOID A CFIT OUTCOME. CRM AND THE FO'S PERFORMANCE WERE EXCELLENT. NO INJURIES WERE SUSTAINED BY ANYONE; AND THE ACFT WAS RETURNED TO SVC AFTER REPLACEMENT OF BOTH MAIN WHEELS AND A THOROUGH BRAKE INSPECTION.