THE WEATHER BEAT · SEP 30

Choi-wan is named, and Saipan and Tinian move from a watch to a Tropical Storm Warning

The Guam weather office upgraded Saipan and Tinian to a Tropical Storm Warning as 26W became Choi-wan, with a typhoon forecast near Alamagan by Friday.

By the Weather Rock September 30, 2026, 8:30 p.m. · 5 min read ShareCopy link

Today, officially

In the space of one night, the storm the Marianas were watching picked up a name and the islands moved from a watch to a warning. At 9:10 a.m. Chamorro Standard Time on Thursday, the Weather Service office in Tiyan, Guam said Tropical Storm 26W had been named Choi-wan. In the same statement it put Saipan, Tinian and their adjacent waters under a Tropical Storm Warning. That is 7:10 p.m. Wednesday on the US East Coast. A warning means tropical storm conditions are expected within 24 hours. The watch it replaced only said they were possible.

The office gave its reason plainly. Choi-wan has picked up forward speed again, and its tropical storm force winds are expected to spread a little to the west and southwest. That keeps Saipan and Tinian, in the statement's words, "well within said wind field." As of 7 a.m. ChST the center was about 370 miles east-northeast of Guam. It was moving west-northwest at 9 mph with winds of 40 mph.

The track is the same one this desk described on Wednesday, only closer. Choi-wan is forecast to keep moving west through Thursday night, turn northwest Friday morning as it approaches Alamagan from the south, and strengthen into a typhoon. It then turns sharply north and moves north-northeast late Friday night. Because the storm slows and bends near the northern islands, the office expects a long stretch of rough weather. It describes "a lengthy period of time of damaging to destructive tropical storm conditions" from Thursday evening into Sunday afternoon. For Saipan and Tinian, the statement says the strongest tropical storm winds look to stay north, packed close to the center. Alamagan and Pagan are the islands it places inside the typhoon force winds, Friday night into early Saturday.

The water may matter as much as the wind. A Coastal Flood Watch covers the north and west facing reefs of Saipan and Tinian through Monday evening, and its impacts section reads "Numerous roads may be closed." The rain comes in two parts. Choi-wan brings rain through the weekend, and the statement says a monsoon surge south of the storm will keep Saipan and Tinian wet into next week. Guam and Rota are under a Wind Advisory from Friday for southwest winds of 30 to 35 mph.

The office's instructions are practical. Take small loose objects indoors. Identify suitable shelter. Stock a few days of food and water. Remain in sturdy shelter until the all-clear.

*Source: NWS Tiyan GU Tropical Storm Warning and local statement, sent 9:10 a.m. ChST 1 October 2026 (23:10Z 30 September); Flood Watch sent 2:57 a.m. ChST; High Surf Advisory and Coastal Flood Watch sent 4:18 a.m. ChST; Wind Advisory for Guam and Rota sent 3:06 a.m. ChST; all read from api.weather.gov at 00:3xZ 1 October. The two rain figures for Saipan and Tinian come from two products and are reported as issued. Times are Chamorro Standard Time (UTC+10).*

This is a morning summary, not emergency information. For live warnings see weather.gov and your local officials. The Guam office posts its products at https://www.weather.gov/gum/, and preparedness guidance is at https://www.ready.gov/.

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