Tropical Depression 23W (#Mirasol) – Tropical Cyclone Advisory #1: 1200 UTC 16 September 2025

Tropical depression forms along the eastern coast of Luzon, likely to bring heavy rainfall to parts of northern Luzon during the next couple of days

Author

Will Weaver
September 16, 2025

…Tropical depression forms along the eastern coast of Luzon… …Likely to bring heavy rainfall to parts of northern Luzon during the next couple of days…

Himawari-9 infrared satellite image (Weathernerds)

Current storm information:

  • Position: 15.8°N 122.8°E

  • Movement: NW at 7 knots (10 km/h)

  • Intensity: 30 knots (55 km/h)

  • Central pressure: 1006 hPa

Trend:

  • Little change in strength is forecast during the next 24 hours.

Watches and warnings:

PAGASA wind signal map (click to enlarge)

  • TCWS #1 (Philippines): Batanes Islands, Babuyan Islands, Ilocos Norte, Apayao, Cagayan, northern Ilocos Sur, Abra, Kalinga, Mountain Province, Ifugao, Isabela, eastern Nueva Vizcaya, northeastern Quirino, northern Aurora, Polillo Island, Catanduanes, and the northern coasts of Camarines Norte and Camarines Sur

Hazards affecting land:

  • The depression is likely to produce areas of heavy rainfall over portions of northeastern Luzon, as well as the Batanes and Babuyan Islands and the southern coast of Taiwan, during the next couple of days. This rainfall could cause isolated flooding in low-lying areas. For additional information, refer to products from your local weather office.

  • Interests in southern China, including Hong Kong and Macau, should monitor the progress of this system.

Discussion:

WSFM MWI 37GHz microwave satellite image. It doesn’t look like much but there is some rudimentary banding wrapping into 23W’s circulation just northeast of Polillo Island.

The area of low pressure off the eastern coast of Luzon has continued to increase in organization since yesterday’s tropical weather outlook. Microwave satellite imagery indicates that some fragmented banding has developed and is wrapping into an increasingly well defined circulation center. A bullseye HYSAT pass from 0959 UTC was able to resolve this circulation center, and a small area of 25 to 30 kt winds is evident primarily to the east of the center. The system is a bit lopsided with most of the convection displaced east of the center by some low to moderate westerly subsidence associated with a mid- to upper-level high pressure area over the South China Sea. Still, the system is organized enough that it can be considered a tropical depression, and the system is now Tropical Depression 23W with winds of 30 kts.

Although TD 23W is in a marginally favorable environment with very warm SSTs offset by the aforementioned westerly shear, it appears unlikely to strengthen significantly before moving inland over northeastern Luzon during the next few hours. Therefore, little change in strength is likely until 23W emerges over the Luzon Strait on Wednesday evening. Once 23W reaches the Luzon Strait, it should run headlong into a very strong subtropical ridge firmly entrenched over the East China Sea and turn sharply westward. The shear is forecast to relax by that point, and this could enable some modest strengthening as 23W approaches southern China. How strong 23W gets will depend on how sharp its westward turn is. The JTWC and JMA forecasts track 23W over southern China by Friday evening and indicate weakening and eventual dissipation, although the operational GFS model and some GFS and ECMWF ensemble members show a track off the coast, and therefore strengthen 23W more. Given that a majority of the ensemble guidance (GFS, ECMWF, and Google DeepMind), as well as the dynamical HWRF and HAFS models, show a track over land, the forecast track below reflects this. However, there is low confidence in that part of the forecast at this time.

Forecast positions and maximum winds

  • 00 hrs: 15.8°N 122.8°E – 30 kts

  • 12 hrs: 17.0°N 122.2°E – 30 kts inland

  • 24 hrs: 18.5°N 121.5°E – 35 kts on the northern Luzon coast

  • 48 hrs: 20.8°N 118.3°E – 45 kts 

  • 72 hrs: 22.0°N 115.7°E – 55 kts 

  • 96 hrs: 22.1°N 113.8°E – 65 kts

  • 120 hrs: 21.8°N 110.8°E – 40 kts inland

JMA forecast map