The weather system moves at the speed of120km per hour. After 24-36 hours,

A, the northeast wind is on the south side of the high pressure, so it does not meet the meaning of the question;

B the pneumatic system moves from west to east at the speed of 120km per day. After 24 hours, the ground A will be located in the southwest of the high pressure center. Under the action of horizontal pressure gradient force and geostrophic deflection force, the ground A mainly blows southeast wind, so it is correct.

C, the northwest wind is on the east side of the high pressure, so it does not meet the meaning of the question;

D, the southwest wind is on the north side of the high pressure, which does not meet the meaning of the question.

Therefore, choose: B.