ACR OVERSHOOTS ASSIGNED ALT WHEN FO IS RELUCTANT TO TAKE CAPT'S DIRECTION.

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TSTMS RPTED; VISUALLY OBSERVED AND MONITORED ON WX RADAR PRIOR TO TKOF. FO WAS FLYING THIS LEG. TKOF WAS UNEVENTFUL; BUT CLOSE PROX TO WX OBVIOUSLY DISTR HIM; AS VECTOR FROM DEP WAS ISSUED TO TURN TO 300 DEG HDG (WX WAS 5-10 MI AWAY). HE BROUGHT NOSE UP TOO HIGH. I TOLD HIM TO LOWER IT; THEN HE USED TOO MUCH ANGLE OF BANK (22 DEGS). 15 DEG ANGLE OF BANK WAS MAX ALLOWABLE AT THIS POINT (LEADING EDGE SLATS EXTENDED). I TOLD HIM TO REDUCE IT; BUT HE ONLY REDUCED IT TO 20 DEGS ANGLE OF BANK. I RECOMMENDED HE ENGAGE AUTOPLT; BUT HE REFUSED. NOW WE WERE CLBING THROUGH 4500 FT WITH 2200 FPM. HE CLBED THROUGH 5000 FT; SO I PUSHED FORWARD ON YOKE TO STOP THE CLB AND ALERT HIM. HE SAID 'I'VE GOT IT.' SO I SLOWLY RELEASED FORWARD PRESSURE; BUT ACFT CONTINUED TO SLOWLY CLB (100-200 FPM); ALT NOW 5200 FT. SO I REAPPLIED FORWARD PRESSURE AND HE SAID 'I'VE GOT IT.' HE BEGAN TO RETAKE CTL AND FLY IT MANUALLY. RECOMMENDATION: WHEN WX BECOMES AN OVERRIDING CONCERN; ENGAGE THE AUTOPLT TO REDUCE WORKLOAD AN ALLOW MORE TIME TO ANALYZE AND INTERP THE WX.