The Coast Guard Navigation Center has published a special notice to mariners that use GPS equipment. The special notice outlines the details of the GPS Week Number Rollover that will occur April 6-7.

To best prepare for the rollover event, users of GPS equipment who are concerned should update their firmware, or contact their equipment manufacturer to ensure their equipment is ready for this event.

When the week number reaches 1024 at 18 seconds before midnight (UTC) on April 6, it will reset to zero as it keeps counting. This has happened once before, in August 1999.

Recent devices have likely been designed to handle the rollover event.

Older GPS receivers, however, or receivers that have not been provided manufacturer updates, may be affected by the rollover. The impact might occur in April, or could affect such equipment at a later date. The date might revert back to August 1999, or may revert to another date. Since this issue does not affect the other parts of the GPS navigation message (it only affects the date), the receiver’s ability to calculate the position and to display the exact time of day should not be impacted.

Additional information about GPS and the GPS Week Number Rollover is available here:

Civil GPS users are encouraged to report disruptions or anomalies to the U.S. Coast Guard Navigation Center or via phone at 703-313-5900, 24 hours a day.