Just noted this on the NOAA/NWS Space Weather Prediction Centre home page.
Effective Wednesday, July 25, 2012, at 1600 UTC (10:00 AM MDT), SWPC will modernize its geomagnetic storm watch products. These products will now be issued relative to the highest expected geomagnetic storm category (NOAA Scale) and will be based on the 3-hour geomagnetic K-index rather than the 24-hour A-index. Watch products will still be valid for the entire UTC day, just as they are under the A-based watches today. This change will better align SWPC's geomagnetic watch products with its geomagnetic warning and alert products and NOAA Scale designations. Product Subscription Service customers are not required to take any action regarding this change. The current A-based watches contain expected geomagnetic storm scale (G-level) information so all subscriptions will be automatically transferred to the new G-based watch products.