OPENING A SECTOR; ZTL CTLR MISJUDGES WINDS ALOFT WHEN ISSUING SEPARATION CLRNC FOR 2 DSNDING ACR'S RESULTING IN AN OPERROR.

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I PLUGGED INTO A BUSY SECTOR. WE DID NOT HAVE STAFFING TO OPEN THE ULTRAHIGH. MY AIRSPACE WAS FL240 AND ABOVE. RIDES WERE BAD; ACFT WERE REQUESTING CHANGES. THERE WERE A LOT OF ACFT SWBOUND ACROSS MY ARR FIX; SO GETTING ATC ARRS DOWN WAS TOUGH. ACFT #1 WAS ON AN 80 DEG HDG; BUT WAS TFC FOR SOMEONE ELSE. ACFT #2 WAS NE OF RMG AND BHM; BUT I COULD NOT GET HIM DOWN BECAUSE OF OTHER TFC. I TURNED ACFT #1 DIRECT RMG; THINKING HE WOULD GO BEHIND ACFT #2. THE WIND WAS STRONG OUT OF W TO NW. I HAD AT LEAST 3 OTHER SITS THAT NEEDED ATTN. WHEN I REALIZED WHAT WAS HAPPENING; ACFT #1'S MODE C SHOWED FL284. I TOLD HIM TO 'MAINTAIN FL290 AND CLB BACK UP IF YOU GO THROUGH IT.' I THEN IMMEDIATELY DSNDED ACFT #2 TO FL240 'SAY ALT LEAVING;' WHICH HE REPLIED 'OUT OF FL280.' AT ONCE I TOLD ACFT #2 TO MAINTAIN FL280; BUT ACFT #2 HAD GONE THROUGH FL277. FACTORS AFFECTING QUALITY OF HUMAN PERFORMANCE: 1) NOT ENOUGH STAFFING TO SAFELY RUN THE OP. THE ULTRAHIGH SHOULD HAVE BEEN OPEN. THE SUPVR ASKED FOR OVERTIME; BUT WAS ONLY AUTH 1. C) NORMAL REQUIRED STAFFING IS 15; TOTAL ON DUTY CTLRS WAS 10. 2) MY DECISION TO NOT SHUT EVERYONE OFF AROUND ME COULD HAVE BEEN A FACTOR; BUT IT IS NOT MY NATURE TO SHUT DOWN THE NAS UNLESS ABSOLUTELY NEEDED. CORRECTIVE ACTIONS: 1) STAFF THE AREA ADEQUATELY. 2) OPEN SECTORS IN A TIMELY MANNER. 3) HAVE TMU MANAGE THE TFC BETTER. TMU CALLED TO TELL THE SUPVR WE WERE GOING TO BE BUSY; BUT DID NOTHING TO MOVE ACFT OUT OF THE SECTOR.