The force that determines the direction of spiral in a hurricane is the Coriolis Effect.

Here's why:

* Earth's Rotation: The Earth rotates on its axis, and this rotation creates an apparent force that deflects moving objects. This force is called the Coriolis Effect.

* Northern Hemisphere: In the Northern Hemisphere, the Coriolis Effect deflects objects to the right. This causes winds in a hurricane to spiral inwards in a counterclockwise direction.

* Southern Hemisphere: In the Southern Hemisphere, the Coriolis Effect deflects objects to the left. This causes winds in a hurricane to spiral inwards in a clockwise direction.

So, the Coriolis Effect is the key player in determining the direction of the spiral in a hurricane.