Tropical Storm Ragasa (24W/Nando) – Tropical Cyclone Advisory #5: 1200 UTC 19 September 2025

…Ragasa expected to begin rapidly intensifying on Saturday…

Current storm information:

• Position: 16.5°N 130.0°E

• Movement: W at 8 knots (15 km/h)

• Intensity: 45 knots (85 km/h) 

• Central pressure: 994 hPa

Trend:

• Rapid strengthening is forecast during the next 24 hours, and Ragasa is expected to become a typhoon on Saturday.

Discussion:

Ragasa has completed its center reformation and has gotten significantly better organized during the past several hours. Convection has blossomed near and to the south and east of the new circulation center, and it sports extremely cold (-85°C) cloud tops. There are not yet signs of an inner core, but there is a band of very intense convection wrapping around the southeastern side of the circulation center that could be described as a partial eyewall feature. Strong northwesterly subsidence associated with an upper-level anticyclone located over and associated with Tropical Depression Mitag continues to impact Ragasa and restrict its poleward outflow channel, but the convection in the northwestern quadrant has gradually expanded during the past few hours, suggesting the subsidence is decreasing. All in all, Ragasa has strengthened, but not rapidly yet - the intensity is increased to 45 kts, based on Dvorak estimates of T2.5 to T3.5, a CIMSS ADT estimate of 49 kts, and a D-PRINT estimate of 45 kts. 

Ragasa continues to wobble in a general west-northwestward direction, likely as a result of the formative nature of its inner core. This motion should become smoother during the next day or so as the ridge located south of Japan gradually weakens and allows Ragasa to gain some latitude. The weakening of the ridge, combined with the breakdown of the upper-level anticyclone associated with Mitag, is expected to contribute to an extremely favorable environment, and Ragasa remains highly likely to rapidly intensify beginning on Saturday. AI-RI and RIPA rapid intensification index parameters continue to be extremely high, with almost unprecedentedly high probabilities of a 65 kt increase in the next 72 hours (70.6% per RIPA). In addition, the HAFS-A model and a number of ECMWF and Google DeepMind ensemble members intensify Ragasa to near Category 5 strength within 72 hours, although the GFS ensembles have backed off somewhat. The wind values in the forecast below remain higher than the JTWC and JMA forecasts and may even still be a bit conservative, but they lie in the middle of the guidance.

All of this translates to Ragasa becoming an extremely dangerous typhoon during the next few days, and it could attain super typhoon strength early Monday as it enters the Luzon Strait. The forecast track is nudged slightly to the north and now shows the center of Ragasa more or less passing between the Batanes and Babuyan Islands on Monday, although confidence in that track is uncomfortably low since there is still quite a bit of spread among the track guidance, with tracks as far north as Taiwan and as far south as coastal northern Luzon. Ragasa is likely to peak on Monday before a gradual increase in shear and a gap wind event in the Taiwan Strait causes some gradual weakening. However, Ragasa is expected to remain an intense typhoon throughout the forecast period as it passes uncomfortably close to Hong Kong and Macau on Tuesday.

Forecast positions and maximum winds

• 00 hrs: 16.5°N 130.0°E – 45 kts

• 12 hrs: 16.7°N 129.2°E – 65 kts

• 24 hrs: 17.4°N 128.1°E – 85 kts

• 48 hrs: 18.9°N 125.2°E – 115 kts

• 72 hrs: 20.0°N 120.8°E – 130 kts

• 96 hrs: 21.2°N 116.1°E – 115 kts

• 120 hrs: 21.5°N 111.1°E – 105 kts

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