B767 First Officer reports encountering a thunderstorm shortly after takeoff with momentary stick shaker activation. Crew elected to accelerate to turbulent air penetration airspeed below 10;000 FT.

Narrative

Change of wind direction during taxi out required runway change. Departure was to south; with left turn after takeoff. Conditions were moderate chop through cleanup; increasing to moderate turbulence as turn completed to south. Heavy rain; hail; turbulence; and windshear conditions were encountered. Normal speed profile was followed; with 250 KIAS flown after cleanup (minimum clean maneuver was only a few knots less). At approximately 7000 FT; a shallow banked turn (approximately 15 degrees) was initiated to avoid continued flight through severe weather. A momentary stick shaker was experienced during turbulence and windshear. Crew selected flight ignition; and exercised the Captain's emergency authority to begin to accelerate to turbulent air penetration speed below 10000 FT. Pilot not flying contacted ATC and advised them of deviation severe weather and suggested discontinuing all south departures. During acceleration; windshear and turbulence increased and a second momentary stick shaker was experienced while wings level. Airspeed indications were changing rapidly; with deviations noted in excess of 20 knots above and below current speed during the acceleration maneuver.