BE36 pilot reports requesting a diversion to BHM due to weather approaching his intended destination; which is granted. Upon switching to BHM Approach; it becomes increasingly apparent that the Controller is not aware of the planned diversion until the field is reported in sight.

Narrative

En route to CRX; my satellite downlink showed heavy rain heading towards CRX. I advised ATC (I believe I was talking to Atlanta Center at the time) and asked to divert to BHM so I could evaluate my options. The Controller promptly cleared me to BHM. As I neared BHM; I was handed off to Birmingham Approach. I advised Approach I was at 6;000 MSL and had information Zulu. Approach responded with the local altimeter setting; but said nothing about which approach to expect. About 10 miles southeast; I told Approach I had the field in sight. At that point; the Controller apparently realized I was planning to land at BHM; since he said that he had not received any word that I was diverting and thought I was still heading to CRX. When I confirmed my intention to divert; he vectored me for a visual approach and I made an uneventful landing. In retrospect; I should have realized the potential for a disconnect on initial contact when Birmingham Approach said nothing about what approach I should expect. Lesson learned; don't assume flight plan changes are always entered into the system or that every controller is made aware of such changes.