Tropical Storm Ragasa (24W/Nando) – Tropical Cyclone Advisory #4: 1200 UTC 18 September 2025

…Depression in the Philippine Sea becomes Tropical Storm Ragasa as it becomes nearly stationary… …Interests in the Babuyan Islands and northern mainland Luzon should closely monitor its progress…

Current storm information:

• Position: 15.7°N 133.0°E

• Movement: Nearly stationary

• Intensity: 35 knots (65 km/h) 

• Central pressure: 1002 hPa

Trend:

• Additional strengthening is forecast during the next 24 hours.

Discussion:

Convection associated with the tropical depression in the central Philippine Sea has continued to consolidate and increase in coverage since the previous advisory. The convection has begun to coalesce into a central dense overcast, consisting of a spiral band of very intense (-80°C cloud tops) convection wrapping into the circulation center. The system continues to experience some northwesterly shear associated with Tropical Storm Mitag well to the northwest, and as a result the poleward outflow channel remains restricted with most of the convection being located to the south of the center. Although Dvorak estimates only range from T1.5 to T2.0, a recent RCM-3 SAR pass indicated the system is producing tropical storm force winds to the south and east of the center, so the system is now Tropical Storm Ragasa with winds of 35 kts.

The models continue to be quite bullish with Ragasa, as it is expected to move into an exquisitely favorable environment during the next couple of days. The tropical storm is forecast to move generally west-northwestward under the influence of very strong ridging situated over the subtropical Philippine and East China Seas, and the track forecast is generally unchanged. Only some modest strengthening is expected during the next day or so until Mitag leaves the picture and its associated subsidence goes away. Virtually all of the models - GFS, ECMWF, Google DeepMind, and HAFS-A - indicate that Ragasa will begin to rapidly intensify beginning on Saturday; RAMMB RIPA guidance indicates a 75.9% chance of an increase of 65 kts in the next 72 hours. Most of the ensemble members deepen Ragasa below 940 hPa during the next 5 days, and at the high end of the guidance, the HAFS-A model notably peaks the system at 162 kts by the end of the forecast period. Rapid intensification is therefore still explicitly forecast and the wind values listed below remain much higher than the JMA and JTWC forecasts. The intensity will likely level off or decrease by the end of the forecast period as Ragasa experiences some land interaction and increased shear while moving through the Luzon Strait.

It is still too soon to determine with any certainty what the extent of Ragasa’s effects will be, although it is becoming increasingly likely that a very intense and dangerous typhoon could affect the Babuyan Islands and parts of coastal northern Luzon on Monday and Tuesday. 

Forecast positions and maximum winds

• 00 hrs: 15.7°N 133.0°E – 35 kts

• 12 hrs: 16.1°N 132.1°E – 45 kts

• 24 hrs: 16.5°N 130.7°E – 55 kts

• 48 hrs: 17.7°N 130.1°E – 85 kts

• 72 hrs: 19.1°N 127.3°E – 105 kts

• 96 hrs: 19.4°N 123.1°E – 130 kts

• 120 hrs: 19.7°N 117.8°E – 120 kts