Having passed through the islands of Micronesia, the system turned west and quickly moved under the influence of a subtropical ridge (STR).

Rammasun posed a significant threat to the Philippine island of Luzon, as it was expected to reach typhoon intensity before making landfall there.

[5] The American National Weather Service stated that an unexpected rise in wind shear kept the system from intensifying much further before reaching Guam.

[15] At around 17:00 Philippine Standard Time (09:00 UTC), Rammasun's eye passed directly over Rapu-Rapu, Albay while the storm was at its initial peak intensity.

[21] The system was subsequently declared a tropical depression during the next day, by both the Japan Meteorological Agency (JMA) and the JTWC with the latter assigning it the designation 09W.

[22][23] Early on July 11, the JTWC reported that the system had intensified into a tropical storm, after they had assessed the intensity slightly higher than the Dvorak estimates from various agencies.

[25] Early on July 12, the JMA reported that the depression had become a tropical storm and named it Rammasun, as the system passed through the Rota Channel to the north of Guam.

[26][27] Later that day as Rammasun moved westwards under the influence of the subtropical ridge of high pressure, the JTWC reported that it had regained tropical storm status after Dvorak estimates from various agencies supported it and the low level structure of the system had improved.

During July 14, both the JTWC and the JMA upgraded Rammassun to a typhoon after Dvorak estimates from various agencies suggested maximum sustained winds of 65 knots (120 km/h; 75 mph).

[36] Though initially expect to maintain that intensity and make landfall before weakening into a tropical storm again due to land interaction, Rammasun further intensified.

Early on July 20, the JMA reported that Rammasun had weakened into a tropical depression before it was last noted later that day over the Chinese Province of Yunnan.

[53][54][55] After TCCOR 2 was declared, all of the non essential agencies of the Guam Government and several business were shut down, including the Judiciary and University.

[54][55][56][57] Six elementary schools around the island were used as storm shelters, while woman who had been pregnant for more than 38 weeks and or high risk were asked to report to the Guam Memorial Hospital.

[54] A TCCOR 1 was subsequently declared during July 11, as destructive winds were expected to impact the island nation within twelve hours.

[57] As a result, all outdoor activity was prohibited until early the next day when the watches and warnings were cancelled after the system was downgraded to a tropical depression.

[70] In the wake of the storm, The National Transmission Corporation of the country said in their statement, "Preparations included ensuring the reliability of communications equipment, availability of hardware materials and supplies necessary for the repair of damages to facilities, as well as the positioning of line crews in strategic areas, to facilitate immediate restoration work.

[73] Philippine National Disaster Risk Reduction and Management Council's head Alexander Pama, in an interview, said "We are already warning the public to be on alert for possible effects of the weather disturbance: landslides, flash floods, strong rains and winds."

[citation needed] The Embassy of the United States in Manila cancelled non-immigrant visa applicant interviews scheduled for July 15 and 16.

Spokesperson Armand Balilo said "Authorities are already on standby to prevent any maritime vessels from sailing as the Philippines braces for Glenda (Ramassun).

[75] Department of the Interior and Local Government Director Edgar Tabell said "All DILG offices in Luzon and Eastern Visayas have been activated to prepare for Glenda.

[87] Gale-force winds were subsequently recorded offshore and on higher ground, before it made its closest point of approach during July 18, as it passed around 390 km (240 mi) to the southwest of Hong Kong.

[87] Over the region at least 51 trees were blown down while there were several reports of fallen objects including a lamp post on the Tsuen Wan flyover.

The city's mayor, Liu Chun-mei, told the Xinhua News Agency that many houses had been damaged and more than 700,000 people evacuated.

[92] Vietnamese authorities ordered an evacuation of people from parts of the northern coast of the country on July 18 in preparation for Rammasun.

Prime Minister Nguyễn Tấn Dũng ordered authorities to help in evacuation and "require all boats to remain close to the shore".

Duong Anh Dien, a government official, told Tuoi Tre that he ordered the cancellation of "all administrative meetings".

The mountainous province of Bắc Kạn, Cao Bằng, Lai Chau, Lạng Sơn and Lào Cai were put on high alert for flash floods and landslides.

[97] After the system had caused damage to the Philippines, China and Vietnam, the name Rammasun was retired at the Third Joint Session of the ESCAP/WMO Typhoon Committee and WMO/ESCAP Panel on Tropical Cyclones during 2015.