After becoming a tropical storm, Zeb proceeded to steadily intensify. Its large inflow spawned a circulation well to the east-northeast, which organized into a separate tropical storm – Alex. Early on October 11, the storm entered the area of responsibility of PAGASA – the Philippine-based weather agency – which gave it the local name "Iliang". Late on October 11, the JTWC upgraded Zeb to typhoon status, or one-minute winds of at least . This was based on the appearance of a banding-type eye on satellite imagery. On October 12, the storm rapidly intensified as it turned more to the west-northwest toward the Philippines. During this time, it caused increased wind shear over the smaller Tropical Storm Alex to the east-northeast, ultimately absorbing it. At 00:00 UTC on October 13, the JTWC upgraded Zeb to super typhoon status, estimating winds of , marking that Zeb attained Category 5 status on the Saffir-Simpson scale. Twelve hours later, the agency estimated that the typhoon strengthened further to a peak of 285 km/h (180 mph), making it the strongest storm of the season. At the same time, PAGASA also estimated peak 10-minute winds of , also designating Zeb as a super typhoon. Late on October 13, the JMA estimated peak 10-minute winds of just east of the island of Luzon. While near peak intensity, the JTWC estimated that winds of extended , and gales extended from the center.