Re: Explain how the eye of a hurricane forms?

That is a very good question.  Unfortunately, science does not have a 
concrete answer yet.  Current theory includes the centrifugal force 
component you mentioned resulting from wind speeds near the center of 
the storm that are too fast for the pressure differences near the 
center.  This results in the centrifuging effect about which you spoke.  

Another component is the ring of thunderstorms surrounding the eye.  At the 
base of the thunderstorms, air is rushing together (a process called 
convergence).  At the top of the thunderstorms, air is rushing apart 
(called divergence).  Since the thunderstorms are arranged in a ring, some 
of the air rushing away from the tops of the thunderstorms meets in the 
center of the circle. This air rushing toward the center of the top of a 
hurricane is then forced down (since the top of the hurricane is at the top 
of the troposphere...the layer of atmosphere where weather occurs).  This 
sinking air inside the ring of thunderstorms results in decreasing 
cloudiness over the center and eventually, if it goes on long enough, 
results in an eye.

As for why the eye doesn't get bigger due to centrifugal force in stronger 
storms, the answer to that may be that the lower air pressure at the 
hurricane's center results in a stronger force than the centrifugal force. 
Observations from inside a hurricane indicate that the centrifugal force 
component may be weak...especially compared to other forces within a 
hurricane.  

In any hurricane, air rotates around the storm toward the center.  It may 
be that the momentum of the air rotating around the storm inwardly toward 
the center of the hurricane becomes balanced by centrifugal force the storm 
exerts near its center...resulting in a certain eye size.  As the air 
pressure at center of a hurricane decreases, the air rotates in toward the 
center at a faster rate...yielding higher momentum air.  Since the 
centrifugal force produced by a hurricane at its center seems to be weak, 
the higher momentum air would reach balance with the centrifugal force 
closer to the center of the storm.  

To get a better idea of how this might work, picture a tetherball.  It is 
on a rope attached to a pole.  As the ball rotates around the pole, 
centrifugal force holds it at the end of the rope.  However, as the rope 
shortens, the seemingly suspended ball gets closer to the pole.  In this 
analogy, the pole is the center of the hurricane and the rope represents 
the increasing force generated by the falling pressure at the center of the 
storm.  In the case of this tetherball though, the centrifugal force on the 
ball keeps it from reaching the pole because the rope called pressure can 
only shorten so much.

Hope this isn't too confusing.  Someday, science will have a firm answer to 
this question.

For detailed and somewhat complicated information about eye formation, see:
 http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqA.html#A11

and for some general information about hurricanes see:
 http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqA.html