The season officially began on May 15, 2003 in the Eastern North Pacific (east of 140°W), and on June 1 in the Central (between 140°W and the International Date Line); both ended on November 30.

[2] On May 16, 2003, the Servicio Meteorológico Nacional (SMN, National Meteorological Service) released their prediction for tropical cyclone activity in the eastern Pacific.

[3] Three later days, National Oceanic and Atmospheric Administration (NOAA) issued its Central Pacific hurricane season forecast, calling for a slightly below-average level of activity due to the expected development of La Niña.

A third system, Tropical Storm Guillermo, weakened to a remnant low just to the east of the Central Pacific Hurricane Center's area of responsibility.

Following the development of a closed low-level circulation, the disturbance was classified as a tropical depression around 18:00 UTC on May 19 roughly 1,060 mi (1,710 km) south-southeast of Cabo San Lucas.

The storm moved slowly to the west and reached its peak on June 18 with 60 mph (97 km/h) winds; around this time, the cyclone displayed an eye-like feature on weather satellite.

Under the influence of strong shear from the southeast, Blanca began to weaken and move erratically, although intermittent bursts of deep convection continued.

This peak was short-lived as an increase in east-northeasterly shear stripped the storm of its convection and caused it weaken back to a tropical depression on July 7.

The northwest motion caused by a mid-level ridge north and northeast of the cyclone brought it over colder water, and the system degenerated into a post-tropical remnant low around 06:00 UTC on July 8.

[21] A tropical wave passed over Central America on July 12 and began to show signs of organization south of the Gulf of Tehuantepec two days later, prompting Dvorak classifications on the system.

[21] Tracking westward on the southern periphery of a ridge, the depression became Tropical Storm Felicia twelve hours later, and forecasters anticipated further strengthening into a minimal hurricane.

[24] A tropical wave entered the eastern north Pacific Ocean on August 1 and began to show signs of organization three days later, including the development of convection and the formation of a surface low.

It acquired sufficient organization to be deemed a tropical depression by 06:00 UTC on August 7 roughly 605 mi (975 km) southwest of Cabo San Lucas.

It maintained this strength for a full day, until outflow from the developing Tropical Storm Hilda about 690 mi (1,110 km) to its east disrupted its convection.

The remnant low entered the Central Pacific and interacted with another weak low-level circulation that would later become Tropical Depression One-C prior to dissipation on August 13.

The resultant disturbance moved west and developed into Tropical Depression Eight-E approximately 690 mi (1,110 km) to the south of Cabo San Lucas around 06:00 UTC on August 9.

Hilda moved west-northwest initially, but increasingly cooler waters weakened the cyclone, and low-level flow across the East Pacific turned the storm west.

It moved northwest and became Tropical Depression Nine-E off Cabo Corrientes by 12:00 UTC on August 22 while it was located about 220 mi (350 km) southeast of Baja California Sur.

The storm tracked northwest across the southern Gulf of California and began to weaken due to land interaction, ultimately making landfall with winds of 80 mph (130 km/h) just to the east of La Paz.

[30] The slow motion of Ignacio produced heavy rainfall across the southern portion of the Baja California Peninsula, including a peak 24‑hour total of 7.25 in (184 mm) in Ciudad Constitución,[32] which was beneficial in ending an ongoing drought but resulted in severe flooding.

[37] The remnants of Ignacio produced thunderstorm activity in high terrain areas of central California, resulting in 3,500 customers losing power, over 300 lightning strikes, and 14 forest fires.

[38] At 06:00 UTC on August 28, an area of disturbed weather within the Intertropical Convergence Zone developed into Tropical Depression Ten-E some 1,725 miles (2,776 km) east of the Hawaiian Islands.

After reaching its peak strength with 105 mph (169 km/h) winds about 800 mi (1,300 km) to the east of Hawaii, Jimena began to weaken as a result of increased shear.

By 12:00 UTC that day, an increase in organization prompted the designation of Tropical Depression Eleven-E roughly 280 mi (450 km) south-southwest of the tip of Baja California.

High pressure to its west facilitated Marty's development, while favorable conditions allowed it to become a Category 2 hurricane with peak winds of 100 mph (160 km/h) early on September 22.

[50] Low wind shear and warm waters favored development, and the depression intensified into Tropical Storm Nora early on October 2.

Although the NHC anticipated further strengthening to major hurricane status, Nora weakened due to increased wind shear from the developing Tropical Storm Olaf to its east.

[62] Moisture from Nora and Olaf interacted with an upper-level low to produce flooding across parts of Texas, forcing a family to evacuate in McGregor.

Olaf moved erratically before ultimately accelerating northward toward the Mexico coast, and it made landfall about 20 miles (32 km) west of Manzanillo with winds of 60 mph (97 km/h) on October 7.

[65] Since Olaf struck the Mexico coastline as a more coherent system than Nora, it produced significantly more rainfall across the region,[66] resulting in severe flooding in the states of Jalisco and Guanajuato.