The first system of the 2009 Pacific hurricane season, One-E formed out of an area of disturbed weather on June 18, 2009, and initially tracked slowly northwards.

Late on June 18, the National Hurricane Center noted that the system was on the verge of becoming a tropical storm; it would have been named Andres had this occurred.

However, the following day, strong wind shear caused the depression to rapidly degenerate into a trough of low pressure before dissipating off the coast of Sinaloa.

[1][2][3] The system continued to organize, and on June 17 the National Hurricane Center (NHC) noted the likelihood for tropical cyclogenesis; although, at the time, the circulation was not well-defined.

[4] It organized further,[5] and on June 18, the NHC initiated advisories on the first tropical depression of the 2009 season about 350 miles (565 km) south-southwest of Mazatlán, Sinaloa.

[5] The depression traveled northward along the periphery of a mid-level ridge over Mexico and an unusually strong mid to upper-level trough situated over the Baja California Peninsula.

[8] By the morning of June 19, the center of circulation was situated along the southern edge of deep convection, indicating that the depression was beginning to degenerate.

[10] At 11:00 am PDT (1800 UTC), the depression reached its peak intensity with winds of 35 mph (55 km/h) and a barometric pressure of 1003 mbar (hPa; 29.62 inHg).

[1] The remnants of the depression were monitored by the United States Naval Research Laboratory for several more hours until the system moved inland over Sinaloa.

[14] Late on June 18, a tropical storm warning was declared for the Islas Marías and the watch along Sinaloa was extended southward to Cabo Corrientes, Jalisco.