watchOS 5.3 (build 16U5537b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-05-28T17:12:27Z. The update package is 196.03 MB. This is a delta (partial) update that requires 5.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 345d889b618324ad5aefc43c02c42b163e7d846a.zip.