Upon entering the western North Pacific Ocean, tropical cyclone warning duties transferred from the CPHC to the Japan Meteorological Agency (JMA), and the JMA first assessed Paka as a 65 km/h (40 mph) storm. The Joint Typhoon Warning Center (JTWC) unofficially assumed warning duties for interests in the United States Department of Defense. Paka continued to intensify after crossing the date line, and from late on December 7 through early the following day it remained a strong tropical storm. However, upper-level wind shear increased, and it again weakened. At 1200 UTC on December 9, the JTWC assessed Paka as an 85 km/h (50 mph) tropical storm and forecast it to continue weakening. By December 10, the shear had begun to decrease as the storm moved through the Marshall Islands, and that night the JTWC upgraded Paka to typhoon status. Paka officially attained typhoon status when JMA classified it with winds of 120 km/h (75 mph) at 0000 UTC on December 11.