Hong Kong Observatory vs US Weather

The Hong Kong Observatory's Open Data API exposes roughly 50 machine-readable datasets covering real-time weather observations, 9-day forecasts, lightning counts, tropical cyclone tracking, tidal predictions, UV index and radiation levels, plus historical rainfall and sunshine records, for Hong Kong and nearby waters. It is a free, keyless service built for machine-to-machine consumption, mirrored on the government's data.gov.hk portal alongside the Observatory's own documented endpoint.

The National Weather Service API serves official US government forecasts, active alerts, and observation-station data as GeoJSON and JSON-LD feeds, with no signup or API key required. It's widely used by third-party weather apps and accepts direct browser calls, though it requires a descriptive User-Agent header identifying your application on every request.