watchOS 5.3 (build 16U5558b) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2019-06-24T17:25:05Z. The update package is 502.07 MB. This is a delta (partial) update that requires 5.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c677fd6b30d0e9be58883cf3b9a8292d5d875dd0.zip.