Tropical Depression (Invest 90W) – Tropical Cyclone Advisory #2: 1200 UTC 17 September 2025

…Tropical depression in the central Philippine Sea poorly organized but expected to strengthen significantly during the next several days…

Current storm information:

• Position: 13.8°N 134.5°E

• Movement: WNW at 9 knots (15 km/h)

• Intensity: 30 knots (45 km/h) 

• Central pressure: 1005 hPa

Trend:

• Some strengthening is forecast during the next 24 hours, and the depression could become a tropical storm on Thursday.

Discussion:

The tropical depression in the central Philippine Sea (invest 90W) is not particularly well organized. Although the system appears to have a well-defined surface circulation, its associated shower activity is rather limited, consisting of clusters of convection rotating rather loosely around the center. CIMSS shear analysis suggests that some northeasterly subsidence associated with a mid- to upper-level anticyclone centered over Luzon is impacting the system and hindering its efforts to organize. The intensity is held at 30 kts, although this could be generous considering that recent Oceansat scatterometer data was not particularly impressive and did not show any winds stronger than 20 kts. 

The forecast is quite problematic given the depression’s current structure (or lack thereof), combined with the fact that it will soon be moving into a much more favorable environment. Nearly all of the available model guidance indicates significant strengthening as TD 90W moves generally west-northwestward at a rather slow forward speed during the forecast period. In fact, the HAFS-A model brings 90W to Category 5 strength within the next 120 hours, and a number of GFS, ECMWF, and Google DeepMind ensemble members deepen the system below 935 hPa. Making matters even more complicated is the fact that there is substantial spread among the track guidance late in the forecast period, with tracks as far north as central Taiwan and as far south as northern Luzon. All of this combines into a low-confidence track but medium-confidence intensity forecast. Given that RIPA rapid intensification guidance shows a high probability of rapid intensification, the forecast below explicitly forecasts it and shows 90W becoming an intense typhoon by the end of the forecast period. Although the wind values given below are higher than the JMA and JTWC forecasts, they are about in the middle of the guidance.

It should be noted that it is still too soon to determine which areas could receive direct impacts from this system.

Forecast positions and maximum winds

• 00 hrs: 13.8°N 134.5°E – 30 kts

• 12 hrs: 15.1°N 133.6°E – 35 kts

• 24 hrs: 16.5°N 132.5°E – 45 kts

• 48 hrs: 16.9°N 131.6°E – 65 kts

• 72 hrs: 17.8°N 130.7°E – 80 kts

• 96 hrs: 19.2°N 128.2°E – 95 kts

• 120 hrs: 19.8°N 124.0°E – 110 kts