Halong formed as a tropical storm on October 5, 2025 in the northern Philippine Sea. Halong strengthened into a typhoon by the next day. On October 7, Halong underwent rapid intensification, becoming a powerful Category Four typhoon.

As the storm approached the Izu Islands of Japan, it weakened to a Category Three typhoon. As Halong passed the islands on October 9, it brought over 8″ (207mm) of rain to Hachijō-jima in just three hours, the highest ever recorded for the area.

After passing the islands, Halong turned eastward and began to weaken. On October 10 near 13:10 UTC, the storm became an extratropical cyclone. The system continued northeastward across the northern Pacific Ocean as a strong storm, heading towards Alaska. By October 11, the extratropical cyclone was near the Aleutian Islands and it moved into the Bering Sea later that day. The remnant low of Halong slammed into the western coast of Alaska on October 12, bringing hurricane force winds, storm surge, and coastal flooding to the remote communities.