SAIPAN — Tropical Depression 17W still has not made its long-awaited northwest turn, and its continued westward drift near Chuuk has nudged the forecast track slightly left, National Weather Service Guam Meteorologist in Charge Brandon Aydlett said in a Facebook briefing Wednesday evening, putting Saipan and Tinian at a 20 to 30 percent chance of tropical storm conditions this weekend.
“We’re still not seeing that northwest motion that we’ve been waiting for. We’ve been talking about it for the past several days. It’s still not come in yet,” Aydlett said. Forecasters had expected the turn as early as Wednesday evening, overnight or into Thursday, and the models still point that way.
The system held 35 mph winds as of 1 p.m., just shy of the 39 mph tropical storm threshold, which Aydlett said could be reached Wednesday evening or overnight as 17W becomes better organized. The latest forecast track still carries an intensifying tropical storm, then typhoon, through the far Northern Mariana Islands, with Saipan and Tinian on the southern edge of the forecast cone.
Aydlett said the leftward drift is what forecasters are watching most closely. “That is one of those things that does make us all sweat here in the Marianas when there’s a deviation that could bring it closer to us,” he said. A shift left of track would mean an increasing threat of impacts for Saipan, Tinian and points south.
Current wind speed probabilities put tropical storm conditions at 5 percent for Guam, near 10 percent for Rota and 20 to 30 percent for Tinian and Saipan, with a 5 to 10 percent chance of typhoon-force winds for Tinian and Saipan. The most likely arrival time for tropical storm force winds in the lower CNMI is around midnight Friday night into Saturday, with the far northern islands near or just after daybreak Saturday. The earliest reasonable arrival, if 17W moves faster, would be Friday afternoon or early evening for the lower Marianas.
No tropical storm or typhoon watches or warnings are in effect for Guam, Rota, Tinian or Saipan, and the Marianas remain outside the 48-hour window in which a watch would be issued. Aydlett noted the weather service is aware of a few people in the northern islands and urged preparation and communication there.
Wednesday’s heavy showers and thunderstorms across the Marianas, which brought a flash flood warning to Guam and flood advisories to Saipan and Tinian, are not the depression itself, Aydlett said, but part of the broader pattern tied to it. Those storms were trending down Wednesday evening, with quieter weather possible before the weekend.
In Chuuk State, a tropical storm watch remains in effect for Fananu, Ulul, Chuuk, Losap and Lukunor, while watches for Pohnpei State islands were canceled Wednesday afternoon as 17W pulls away. Aydlett said central and eastern Micronesia will still see west to southwest gusts exceeding 35 to 40 mph, torrential rainfall with flash flood and mudslide concerns and dangerously choppy seas through Thursday night and Friday, and he urged islanders to reconsider inter-island travel.
For the Marianas, southwest winds are expected to build from late Saturday into Sunday and Monday, bringing increasing showers and choppier seas regardless of 17W’s exact path.
“The trends are what matter right now,” Aydlett said.
