Champi exploded into a 150-mph super typhoon hours before Guam’s typhoon warning came down

Super Typhoon Champi (29W) carried sustained winds of 150 mph when the National Weather Service in Guam lifted the typhoon warning for Guam and Rota at 5:51 p.m. Chamorro Standard Time on Sunday, October 18. The storm, a 70-mph tropical storm late on Friday, was by then about 170 miles west of the island and still moving away.

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The cancellation says nothing about the storm weakening. Guam had simply fallen outside the typhoon’s wind field, and forecasters expected the system to keep strengthening as it travelled west toward open water.

NWS Guam Advisory 15 and the 150-mph reading

The cleanest statement of the intensity comes from NWS Guam’s Super Typhoon Champi Advisory Number 15, issued at 1:31 p.m. ChST on October 18. It put maximum sustained winds at 150 mph, with the center at 13.2 degrees north and 142.9 degrees east, about 130 miles west of Guam and moving west at 16 mph. Typhoon-force winds reached up to 60 miles from the center and tropical-storm-force winds up to 160 miles. The advisory left the typhoon warning for Guam, Rota and adjacent coastal waters in place, and it said the storm could become a Category 5 super typhoon early Monday morning.

The Joint Typhoon Warning Center supplies the underlying analysis and reached the same number in knots. JTWC Warning No. 015, valid at 0300 UTC on October 18, listed 130 knots with gusts to 160 knots and a minimum central pressure of 934 millibars, placing the center about 72 nautical miles west-southwest of Naval Station Guam. Its forecast table topped out at 140 knots, roughly 161 mph, within 24 to 48 hours, then eased to 105 knots by day five.

The 5:51 p.m. cancellation and the wind advisory left behind

NWS Guam’s local statement, as relayed on Meteoblue’s Guam warnings page, carried the line “TYPHOON WARNING IS CANCELLED FOR GUAM AND ROTA.” The same statement logged Champi at 150 mph at 5 p.m., about 170 miles west of Guam and moving west at 10 mph, with heavy rainbands reaching roughly 100 miles east of the center. The 150-mph reading in the 1:31 p.m. advisory therefore predates the cancellation by about four hours and 20 minutes, which is the interval the storm spent leaving the island’s wind field at full strength.

What stayed behind was a wind advisory. Southeast winds of 25 to 35 mph were forecast for Guam and Rota until 4 a.m. on October 19, with the warning that “Tree limbs could be blown down and a few power outages may result.”

Eyewall replacement and the Category 5 forecast

The 5 p.m. statement added a technical caveat: the eye was obscured, and Champi appeared to be undergoing an eyewall replacement cycle, the process in which a second ring of thunderstorms forms outside the first and starves it. Such cycles often weaken a storm briefly before it restrengthens. The Watchers, a hazards-tracking site, reported that by 1200 UTC on October 18 JTWC had Champi at 140 mph after a second eyewall formed and dry air entered the circulation, with a forecast to regain 150 mph by 0000 UTC on October 19.

That reporting also puts the earlier intensification on a clock. The Watchers wrote that Champi passed about 10 miles south of Merizo, Guam, at 1826 UTC on October 17, which was 4:26 a.m. ChST on October 18, and was upgraded to a super typhoon roughly three hours later. Scripps News, writing on October 16, had described a 70-mph tropical storm that forecasters expected to become a typhoon early Saturday and a Category 2 storm near Guam on Sunday, with the National Weather Service advising preparation for winds near 100 mph. A system forecast to reach about 100 mph instead sat at 150 mph by Sunday afternoon, a gain of roughly 80 mph in under two days.

Condition of Readiness 1 after the warning

Cancelling the warning did not end the emergency response. Guam Homeland Security and the Office of Civil Defense, in Joint Information Center Release No. 14 posted at 12:45 p.m. ChST on October 18, kept the island at Condition of Readiness 1 and told residents to stay in a sturdy, concrete-reinforced structure until Condition of Readiness 4 is announced. The release said tropical-storm-force winds of 40 to 50 mph, gusting to 60 mph, could continue into the afternoon, closed all public schools on Monday, October 19, for damage assessment, and reported that about 51 percent of the Guam Power Authority’s distribution feeders were online as of 9 a.m., with outages worst in southern Guam and no island-wide blackout.

NWS Guam’s tropical cyclone products page describes the Local Statement as the island-specific product issued every six hours while watches or warnings are active, and the Public Advisory as a plain-language version of the JTWC warning. With the Guam warning cancelled, the JTWC warning numbers and the NWS public advisories carry the storm’s track from here.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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