A USPS Status Alert can mean several different things.
However most commonly when you get a USPS Status Alert on your tracking information it means that your USPS package is undergoing unusual shipping conditions.
Or it can also mean that your package has been lost but they are trying to find it.
Other causes of a USPS Status Alert are refusal by the recipient, absence of the recipient, expiry of collection deadline, customs issues/or item loss, damage, etc.
If the package does not show up on the expected delivery date or the tracking Status Alert does not update then contact USPS or go to your local post office with the tracking number.
They can help you locate the package.