The system reached its peak intensity on June 17, at 15:00 UTC, with maximum sustained winds of 80 knots (90 mph; 150 km/h) and a central pressure of 976 mbar (28.82 inHg).

[3] Late on June 10, a broad low-pressure area formed off the coast of southwestern Mexico, producing disorganized showers and thunderstorms in an environment conducive for gradual development.

[10] Blas then developed a mid-level eye on the western portions of the cyclone,[11] then maintained its intensity due to very cold cloud tops near the center and a strong upper-level outflow in three of the storm's quadrants.

[12] Blas strengthened slightly on June 17, with its maximum sustained winds increasing to near 90 mph (140 km/h) and a minimum central barometric pressure of 976 mbar (28.82 inHg).

[15] The storm continued to weaken that day, with satellite images showing a partially exposed low-level center with convection confined to the southeastern quadrant of its circulation.

[16][17] Despite persistent wind-shear and transiting over cool waters with temperatures below 79 °F (26 °C), Blas maintained limited convection on the eastern half into June 19.

[20] With little or no convection remaining in association with Blas, along with their being no longer tropical-storm force winds in the circulation, the NHC downgraded the storm to a tropical depression six hours later.

[21] By 15:00 UTC that same day, Blas transitioned to a post-tropical cyclone about 350 mi (565 km) southwest of the southern tip of the Baja California peninsula.