Apple has begun sending out emails notifying iCloud members of imminent storage downgrades to their accounts, The Unofficial Apple Weblog said.

The emails have been sent to iCloud members who were previously paid MobileMe subscribers.

When Apple transitioned to iCloud from MobileMe the company gave a temporary extra 20 GB of space to MobileMe subscribers as an incentive to move to iCloud. The extra space was originally set to expire on June 30 of this year, but in May Apple extended the expiration date until the end of September.

As Apple reminds people in the email it sent out Sept 24, now the extra 20 GB allowance expires on Sept 30, 2012. After that date, those iCloud customers will be downgraded to the normal 5 GB plan unless they choose to pay for an upgrade.