Forming out of a tropical wave on July 30, 1997, roughly 345 mi (555 km) south of Salina Cruz, Mexico, Guillermo tracked in a steady west-northwestward direction while intensifying.

The remnants persisted for more than a week as they tracked towards the northeast and later south and east before being absorbed by a larger extratropical system off the coast of California on August 24.

However, because of its extreme intensity, it produced large swells across the Pacific Ocean, affecting areas from Hawaii to coastal Mexico.

The National Hurricane Center (NHC) stated that they had issues monitoring the system as it moved through the Caribbean; however, they interpreted through satellite data that the wave crossed Central America and entered the Pacific Ocean between July 27 and 28.

In response to a deep-layer ridge to the north, the depression tracked at a steady pace towards the west-northwest, and this motion persisted through the first week of August.

[1] Operationally, Guillermo was thought to have briefly leveled out in intensity on August 2;[2] however, in post-storm analysis, the NHC discovered that a steady period of rapid intensification took place.

[6] After maintaining this intensity for roughly 18 hours, the system began to weaken as it moved into a less favorable environment with moderate wind shear.

By August 8, Guillermo moved over colder waters and was downgraded to a tropical storm as sustained winds dropped below 75 mph (121 km/h).

Around this time, the storm started to move along the western edge of the ridge that previously steered it towards the west-northwest, causing Guillermo to turn northwest.

On August 9, the storm crossed longitude 140°W, denoting a shift in warning responsibility from the NHC to the Central Pacific Hurricane Center (CPHC).

[7] Later that day, Guillermo transitioned into an extratropical cyclone at an unusually high latitude of 41.8°N,[1] roughly 850 mi (1,370 km) south-southeast of Unalaska, Alaska.

[9] On August 24, Guillermo's remnant low was finally absorbed by a larger extratropical system, while situated roughly 345 mi (555 km) off of the northern California coastline.

[10] Due to accurate forecasts, emergency officials across California were able to close off swimming zones and warn the public about dangerous rip currents prior to their arrival.

On August 6, a teenage boy and girl were injured on a beach in Corona Del Mar, while an 18-year-old was pulled ashore and sent to the hospital with neck injuries.

[15] In addition to coastal impacts, the system brought a surge of warm, moist air into Southern California, bringing temperatures in some areas as high as 110 °F (43 °C).