Actually, most of the Pacific information comes from the Joint Typhoon Warning Center, which is a US Navy and Airforce service out of Pearl Harbor. They cover the entire Western Pac. The link is below. The local HK office basically uses their information and adds local details and warnings. The current prognostic reasoning indicates the Typhoon will be 180NM or nautical miles from Hong Kong on the 21st. As such, landfall is indicated very close to HK. Should be interesting.
Joint Typhoon Warning Center (JTWC)