watchOS 5.3 (build 16U5558b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-06-24T17:25:02Z. The update package is 190.08 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: 56a395a7a4182425f64e44687e3f6f70aa580162.zip.