THE WEATHER BEAT · OCT 2
Choi-wan becomes a typhoon, and Alamagan, Agrihan and Pagan are under a Typhoon Warning
Choi-wan became a typhoon near Pagan, and the Guam weather office has Alamagan, Agrihan and Pagan under a Typhoon Warning as it strengthens.
Key points
- Choi-wan is now a typhoon. In its 8:26 a.m. ChST statement on Saturday, 3 October, the Weather Service office in Tiyan, Guam said a Typhoon Warning remains in effect for Alamagan, Agrihan and Pagan in the northern Marianas. On the US East Coast that was 6:26 p.m. EDT Friday.
- At 7 a.m. ChST the center was 55 miles west-southwest of Agrihan, with winds of 85 mph. The office forecast Category 2 strength as it passes Agrihan Saturday and Category 3 Saturday night as it moves away.
- Saipan and Tinian stay under a Tropical Storm Warning. A Flood Watch covers Guam, Rota, Saipan and Tinian through late Sunday night, and a Coastal Flood Watch covers the north and west facing reefs of Saipan and Tinian through Monday evening.
Today, officially
On Wednesday this desk wrote that Choi-wan was forecast to become a typhoon near Alamagan. By Saturday morning in the Marianas it had. The Guam office's local statement, sent at 8:26 a.m. Chamorro Standard Time, calls it Typhoon Choi-wan (26W). At 7 a.m. ChST the center was about 235 miles north-northwest of Saipan and 55 miles west-southwest of Agrihan, with maximum sustained winds of 85 mph. Agrihan was under only a Tropical Storm Watch on Wednesday. It now shares the Typhoon Warning with Alamagan and Pagan.
The statement put the typhoon winds in the north. It said winds of 74 mph or more would continue for Alamagan, Agrihan and Pagan into Saturday afternoon, as the storm moves north through the northern islands and strengthens. The office forecast Category 2 as Choi-wan passes northwest of Agrihan on Saturday and Category 3 that night as it pulls away. Tropical storm winds of 39 to 73 mph, it said, look to continue on either side of the typhoon winds through at least Sunday morning.
Saipan and Tinian are south of the center, but not out of it. The statement said the monsoon surge along Choi-wan's southern side would keep tropical storm conditions on Tinian and Saipan for the rest of Saturday. It also forecast heavy downpours and gusts occasionally over 60 mph at Guam and Rota. The two products describe the storm's motion differently. The statement had it moving north at 6 mph. The Flood Watch, sent about 100 minutes earlier, called it nearly stationary and expected it to pivot north-northeast through the weekend near Pagan and Agrihan. Both are reported here as issued.
The water may last longer than the wind. The statement said surf on north, south and west facing reefs would run 10 to 14 feet and rise by several feet at nearest passage. For all three northern islands it expected significant coastal erosion and some coastal inundation. On Saipan and Tinian, the Coastal Flood Watch's impacts section reads "Numerous roads may be closed."
The office's instructions are short: stay indoors in heavy rain and strong wind, follow local emergency managers, and remain in sturdy shelter until the all-clear is given.
| Item | As issued |
|---|---|
| Storm | Typhoon Choi-wan (26W) |
| Position, 7 a.m. ChST Sat 3 Oct | 18.4N 144.9E, about 235 miles NNW of Saipan, 55 miles WSW of Agrihan |
| Motion | north (10 degrees) at 6 mph per the statement; "nearly stationary" per the Flood Watch |
| Intensity | 85 mph; forecast Category 2 Saturday, Category 3 Saturday night |
| Typhoon Warning | Alamagan, Agrihan, Pagan |
| Tropical Storm Warning | Saipan, Tinian and adjacent waters |
| Coastal waters, Saipan and Tinian | southwest wind to 45 kt, gusts to 60 kt, seas 14 to 20 feet |
| Surf | 10 to 14 feet on north, south and west reefs of the northern islands (statement); 10 to 14 feet on north and west reefs of Saipan and Tinian, 8 to 12 feet on Guam and Rota (High Surf Advisory, until 4 a.m. ChST Monday) |
| Rain | 8 to 14 inches by early Monday, up to 20 inches near the center (statement); 5 to 8 inches for Saipan and Tinian, 4 to 6 inches for Guam and Rota (Flood Watch, through late Sunday night) |
| Guam and Rota | Wind Advisory, southwest 25 to 35 mph, gusts to 45 mph, until 4 a.m. ChST Sunday |
*Source: NWS Tiyan GU, all read from api.weather.gov at about 00:00Z 3 October: the local statement filed as the Saipan and Tinian Tropical Storm Warning, sent 8:26 a.m. ChST 3 October; the coastal waters Tropical Storm Warning, sent 8:50 a.m. ChST; the Flood Watch, sent 6:47 a.m. ChST; the High Surf Advisory and Coastal Flood Watch, sent 4:00 a.m. ChST; the Wind Advisory, sent 2:46 p.m. ChST 2 October. The Typhoon Warning is quoted from the local statement. The rain figures 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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