Within a favorable atmosphere, Rosa entered a period of rapid intensification on September 27, peaking as a Category 4 hurricane with maximum sustained winds of 150 mph (240 km/h) a day later.

Over the next few days, Rosa turned north and then northeast while steadily weakening, making landfall in Baja California as a tropical depression on October 2.

[1] The National Hurricane Center (NHC) issued a Tropical Weather Outlook on September 19, anticipating that an area of low pressure would form in the Gulf of Tehuantepec over the weekend.

[1] At the time of its formation, the depression was located within a favorable tropospheric environment of warm sea surface temperatures and minimal vertical wind shear, featuring a well-defined center of circulation under an expanding area of strong convection.

[1][6] The NHC remarked that Rosa's structure was well developed at the middle levels of the troposphere, with distinct rainbands wrapped around the southern semicircle of the cyclone.

[9] Rosa turned to the northwest on the afternoon of September 28 in response to an approaching mid- to upper-level trough, which would continue to influence the remainder of the hurricane's development.

[1][12] However, Rosa began to experience impinging wind shear from the developing trough, causing a misalignment between the upper and lower levels of the hurricane,[13] as well as coinciding with a final weakening phase.

[12] The unrelenting wind shear – combined with progressively cooler seas and drier air – quickly eroded Rosa's core, disrupting the eye and convection over the southern half of the hurricane.

[17] At 11:00 UTC on October 2, Rosa made landfall about 70 mi (110 km) southeast of Punta San Antonio in Baja California,[1] becoming the first tropical cyclone to move over the state since Nora of 1997.

[18][19] During its approach towards the Gulf of California, Rosa exhibited an increasingly unwound and diffuse structure, prompting the NHC to declassify it as a tropical cyclone at 15:00 UTC.

[22] The Government of Mexico issued a tropical storm watch on September 29 for the Pacific Coast of the Baja California Peninsula from Punta Abreojos to Cabo San Quintín.

[34] Farther south, in the state of Colima, floodwaters swept through the city of Manzanillo, causing sinkholes, rupturing underground pipes, and inundating buildings.

[38][39] Flood watches and warnings were issued on September 30 for Southern California, Arizona, southwest Colorado, Utah, central Nevada, and a small portion of southeast Idaho.

[22] The remnants of Rosa caused flash floods throughout the communities of Guadalupe, Glendale, Scottsdale, Fountain Hills, Deer Valley, and Sun City[48] and knocked out power in Yuma.

[52] Engineers were recruited to carry out assessments of the dam,[54] and authorities continued to monitor the water level for two weeks before allowing residents to return to their homes on October 17.

[56] The Federal Highway Administration announced on September 10, 2019, that it was providing $4.7 million to the state of Arizona to fund road and bridge repairs required as a result of Rosa.