[3] This quick evolution of the storm continued, and a small but defined central dense overcast became evident on satellite imagery.

[4] This, bundled with increasing satellite estimates, allowed the National Hurricane Center (NHC) to upgrade the depression to Tropical Storm Douglas at 03:00 UTC, July 21.

[5] Well-defined banding developed on the storm's western side, while thunderstorms near the center gathered into a comma head shape.

[9] Convection re-developed, and a ragged eye became briefly evident on satellite imagery, indicating Douglas had strengthened to low-end Category 1 hurricane intensity.

[10] Douglas jumped to Category 3 major hurricane status, as rapid intensification continued, and the storm became larger in size.

[11] Intensification slightly leveled off as the day went on, but the formerly-ragged eye became very warm and symmetrical, indicating the storm had entered a more stable state.

[12] Despite this, a regrowth of the eyewall began, and Douglas reached its peak intensity as a Category 4 hurricane at 21:00 UTC on July 23, with maximum 1-minute sustained winds of 130 mph (210 km/h) and a minimum central pressure of 954 millibars (28.2 inHg).

[13][14] On July 24, visible imagery revealed Douglas' eye had become increasingly cloud-filled, while the storm's overall satellite appearance degraded.

[22][23] Nonetheless, the storm remained in rather healthy condition, despite being situated over cold sea surface temperatures and experiencing wind shear near Hawaii.

[31][13] Douglas' post-tropical low entered the Western Pacific basin later on July 30,[32] before opening up into a trough at 06:00 UTC that day.