1975 Pacific Northwest hurricane

1975 Pacific Northwest hurricane

Category 1 hurricane (SSHWS/NWS)
The hurricane near peak intensity
Formed	August 31, 1975
Dissipated	September 5, 1975
Highest winds	1-minute sustained: 75 mph (120 km/h)
Lowest pressure	990 mbar (hPa); 29.23 inHg
Fatalities	None reported
Damage	None
Areas affected	Western Canada, Northwestern United States (Both while extratropical)
Part of the 1975 Pacific hurricane season

The 1975 Pacific Northwest hurricane was an unusual Pacific tropical cyclone that attained hurricane status farther north than any other Pacific hurricane. It was officially unnamed, with the cargo ship Transcolorado providing vital meteorological data in assessing the storm. The twelfth tropical cyclone of the 1975 Pacific hurricane season, it developed from a cold-core upper-level low merging with the remnants of a tropical cyclone on August 31, well to the northeast of Hawaii. Convection increased as the circulation became better defined, and by early on September 2 it became a tropical storm. Turning to the northeast through an area of warm water temperatures, the storm quickly strengthened, and, after developing an eye, it attained hurricane status late on September 3, while located about 1,200 miles (1,950 km) south of Alaska. After maintaining peak winds for about 18 hours, the storm rapidly weakened, as it interacted with an approaching cold front. Early on September 5, it lost its identity near the coast of Alaska.

On August 26, the tropical cyclone that was once Hurricane Ilsa degenerated into a remnant low pressure area about 1,200 miles (1,950 km) west of the southern tip of the Baja California Peninsula. The remnants of Ilsa drifted northwestward through the field of the eastern north Pacific Ocean. At the same time, a mid-tropospheric trough slowly intensified while gradually undergoing cyclogenesis to develop into a cold-core upper-level low. Early on August 31, a low-level circulation formed within the upper-level low about 930 miles (1,500 km) northeast of Hawaii; at that time, the circulation and the remnants of Ilsa were located within 370 miles (600 km) of each other. The cold-core low rapidly intensified as convection increased, and late on August 31 it absorbed the remnants of Ilsa, which influenced the development of the system. Convection steadily organized as it tracked westward, and it is estimated it transitioned into a subtropical depression by 18:00 UTC on September 1.