On September 6 at 06:00 UTC, the Joint Typhoon Warning Center (JTWC) began monitoring an area of convection approximately 140 nautical miles (260 km; 160 mi) southwest of Manila, assessing its development potential as low.

[1] The next day at 20:00 UTC, its development potential was upgraded to medium as it continued northeastward, with satellite imagery depicting a partially exposed low-level circulation.

[7] The depression continued westward, being steered by a low to mid-level subtropical ridge, and on September 10 at 06:00 UTC, the JTWC upgraded 27W to a tropical storm as it was located approximately 80 nautical miles (150 km; 90 mi) south-southeast of Kaohsiung.

[6][8] 27W was located in a favorable environment with high sea surface temperatures,[9] with infrared satellite imagery showing a small storm and flaring convection obscuring its circulation.

[18] Barijat brought increased risk of flooding and landslides in the provinces of Batanes, Cagayan, and Isabela, with the soil saturation worsening the effects of Typhoon Mangkhut.

[20] 40 thousand residents were evacuated in the cities of Zhanjiang and Maoming,[21] with passenger and train services being halted due to safety concerns.