Storm activity in the Central Pacific Hurricane Center's area of responsibility was below average, with no tropical cyclones forming in the region.

[nb 1][5] The passage of an eastward-moving kelvin wave generated a broad area of low pressure within the Intertropical Convergence Zone well south of Mexico on May 11.

A ridge extending from Mexico into the eastern Pacific forced the depression west, while low wind shear and warm ocean temperatures allowed it to become Tropical Storm Aletta by 00:00 UTC on May 15.

Aletta weakened to a tropical depression as it curved northeast early on May 17, and despite producing intermittent bursts of convection for a few days, ultimately degenerated to a remnant low around 06:00 UTC on May 19.

As the system moved west-northwest, upper-level winds gradually diminished, allowing Bud to attain hurricane strength by 00:00 UTC on May 24.

[7] A trough over the southwestern United States directed the storm northeast, while increasing southwesterly wind shear prompted weakening.

After the storm moved ashore, it rapidly weakened over the mountains terrain of southern Mexico, degenerating to a remnant low around 00:00 UTC on June 17 and dissipating over Guerrero twelve hours later.

[11] The storm made landfall in southern Mexico, bringing with it heavy rains and gusty winds which caused flash floods and numerous landslides along the area, primarily the state of Oaxaca.

[15] A quick-moving tropical wave left Africa on June 23 and emerged into the East Pacific late on July 4, where it interacted with a disturbance within the ITCZ.

A mid-level ridge extending west from Mexico directed the cyclone west-northwest, while a favorable environment allowed Emilia to intensify.

Hampered by strong upper-level winds across the central Atlantic, it entered the East Pacific on August 2, where interaction with a kelvin wave led to an uptick in convection.

On a west-northwest heading, the newly formed system intensified within a favorable environment, attaining hurricane strength by 18:00 UTC on August 8 and reaching peak winds of 80 mph (130 km/h) several hours later.

The storm also brought intervals of heavy showers, gusty winds exceeding 40 mph and hot temperatures in most municipalities in Sinaloa.

[31] Ileana would not maintain hurricane strength for long, and, as predicted, weakened back to tropical storm status on August 31 as it began to turn west.

[32] Weakening continued as Ileana traversed cooler sea surface temperatures and encountered increasing wind shear and more stable air environment.

[36] The next day, the depression became the tenth storm of the 2012 season; however, no significant strengthening was anticipated because of moderate to high vertical wind shear in addition to the marginally warm sea surface temperature along John's path.

[41] John brought rain and wind to the Baja California Peninsula; the Los Cabos port was closed for small craft.

[57] On September 23, rapid intensification was noted as a distinct possibility[58] as vertical wind shear was forecast to remain under 5 knots for the next 36 hours.

[60] Miriam continued to intensify on the 24th, developing a 10 nautical mile wide eye[61] and by 8 am PDT that day, it became a Category 3 major hurricane with maximum sustained winds of 120 mph.

[64] Miriam continued to steadily weaken over colder sea surface temperatures and became a tropical depression on the 27th as the last of the deep convection dissipated, as the moisture separated from the storm, and began streaming over Baja California.

[68] Early on September 25, the National Hurricane Center began monitoring an area of disturbed weather a few hundred miles south of Acapulco, Mexico.

[70] Satellite, ship, and buoy observations early on September 28 revealed that the low had become much better defined, and at 1500 UTC, the first advisory was issued on Tropical Storm Norman, located at the time about 85 mi (135 km) east of Cabo San Lucas, Mexico.

[78] Over the next several hours, a convective cloud band gained curvature over the northwest quadrant of the circulation and a central dense overcast persisted,[79] and on this basis and Dvorak classifications, Fifteen-E was upgraded to Tropical Storm Olivia with an estimated wind speed of 45 mph.

[81] Olivia continued moving northward, but with no change in strength until the afternoon of October 8, when the low-level circulation became exposed to the southwest of the main area of deep convection around 6:00 AM PDT.

[85][86] Early on October 10, the National Hurricane Center first began monitoring a trough of low pressure off the southern coast of Mexico.

[87] Initially, upper-level winds were only marginally favorable, and although the thunderstorms remained disorganized, the NHC estimated a 50% chance for development by early on October 12.

[90] Warm waters, very little wind shear, and a moist environment allowed Paul to quickly intensify and developed organized rainbands.

On October 14, Paul began moving northward while rounding a ridge, also influenced by an upper-level low west of Baja California.

It developed a well-defined surface low four days later, and an increase in deep convection and its organization resulted in the formation of the final tropical depression of the season at 6:00 UTC on October 30.

Moving northwestward to westward under a weak low-level ridge, Rosa gradually intensified until it reach its peak intensity with 50 mph winds and a minimum pressure of 1,001 millibars early the next day.