The ninth named storm of the 2015 Pacific typhoon season, Chan-hom developed on June 29 from a westerly wind burst that also spawned Tropical Cyclone Raquel in the southern hemisphere.

While near the island, the storm dropped heavy rainfall on neighboring Guam, causing flooding and minor power outages.

Jeju Island offshore South Korea recorded 1,250 mm (49 in) of rainfall, and one person died due to a thunderstorm in the country.

During June 2015, a near record strength pulse in the Madden–Julian oscillation, lead to a period of significant weather across the Western Pacific.

[1][2] This significant weather included a major westerly wind burst during late June, which caused a set of twin tropical cyclones to develop.

[4][nb 1] Drifting generally northward, the disturbance slowly organized within a region of low to moderate wind shear and favorable outflow aloft.

[7] Following further organization, the JTWC issued a Tropical Cyclone Formation Alert that day at 22:30 UTC with the system located about 345 km (214 mi) northeast of Pohnpei.

[9] Upper-level ventilation allowed for growth of the cyclone,[12] but moderate wind shear displaced the center from the deepest convection for much of July 1.

[7] Early on July 2, the large circulation of Chan-hom absorbed a smaller disturbance to its southeast,[14] and the storm turned to the west-southwest.

Dvorak satellite classifications indicated that the system reached typhoon intensity following an expansion of the central dense overcast; the JTWC classified Chan-hom as such by 15:00 UTC,[15] although the JMA maintained it as a severe tropical storm.

[7] Shortly thereafter, strong wind shear from a tropical upper tropospheric trough (TUTT) cell to the northeast dramatically weakened the storm.

[16][17] Alongside the shear, subsidence over the cyclone, a trough to the north, and a remnant vortex to the northeast all served to suppress convection.

[19] Coinciding with Chan-hom's abrupt collapse on July 3, the system turned northeast as it entered a weakness in the steering ridge.

[20] Wind shear eased early on July 4 as the TUTT cell retreated to the north and the subtropical ridge steadily re-established itself.

[24][25] Once clear of the Mariana Islands, steady development ensued owing to low wind shear and good outflow.

[30] Chan-hom's eye briefly improved in structure before entering a state of flux and collapsing later that day; convection on the northern side of the storm diminished simultaneously.

[36] The typhoon reached its peak strength during this time with estimated winds of 165 km/h (103 mph) and a barometric pressure of 935 mbar (hPa; 27.61 inHg).

[41] Early on July 11, the typhoon reached the southwestern edge of the subtropical ridge and began turning to the north and later north-northeast.

[47][48] Around 18:00 UTC, Chan-hom moved ashore on the Ongjin peninsula in North Korea, southwest of the capital Pyongyang, with winds of 85 km/h (53 mph).

[45] The rains caused widespread flooding in eastern China;[50] 11 rivers in Zhejiang surpassed the warning level of 1.91 m (6.3 ft).

[55] Winds from Chan-hom were strong enough to knock down street signs across Zhejiang, as well as destroying an unoccupied building in Cixi City.

[53] The high agriculture damage – estimated at ¥3.62 billion (US$583 million) – was mostly due to the typhoon's concurrence with the local harvesting of vegetables and melons.

[50] On the other side of the Rota Channel, Andersen Air Force Base on northern Guam recorded wind gusts of 117 km/h (73 mph).

[49] The remnants of Chan-hom later impacted southern areas of Khabarovsk Krai, producing heavy rain and high winds, peaking at 79 km/h (49 mph).

[77] The towns of Bikin, Sovetskaya Gavan, and Vyazma, saw 40 to 80 mm (1.6 to 3.1 in) of rain or roughly 60–70 percent of their average monthly precipitation for July during the storm's passage.