Tropical Depression (Invest 90W) – Tropical Cyclone Advisory #1: 1800 UTC 3 November 2025

…Tropical depression forms well to the southeast of Guam…

Current storm information:

• Position: 8.1°N 147.8°E

• Movement: W at 5 knots (10 km/h)

• Intensity: 30 knots (55 km/h)

• Central pressure: 1004 hPa

Trend:

• Some gradual strengthening is forecast during the next 24 hours.

Discussion:

The area of low pressure located southeast of Guam appears to have developed a well-defined surface circulation center. Recent scatterometer data from Oceansat-3 indicates that the low has a fairly broad and slightly elongated circulation center with a wide swath of 25 to 30 kt winds located primarily to the east of the center. Convective banding has also increased in that particular sector of the system, with new bands beginning to flare closer to the center. Despite the system’s rather broad nature, it appears to have enough organization to be classified as a tropical depression, and its initial intensity is set to 30 kts based on the scatterometer data and available Dvorak estimates of T1.0 to T2.0.

This system has a rather complicated future ahead of it. Although the system is currently situated beneath a strong ridge centered well to the north, a shear line draped across the Philippine Sea is eroding this ridge. This will likely result in TD 90W beginning a rather erratic northwesterly motion during the next couple of days. Unfortunately, the models disagree significantly on exactly how much the ridge will weaken - the GFS and ECMWF ensemble models have a huge amount of spread, with tracks as far west as Hong Kong and as far east as Iwo Jima. The Google DeepMind (GDM) ensemble is in better agreement on a track further west, toward northern Luzon. The one consistent thing is that all of the models depict significant strengthening, with most of the GDM, GFS, and ECMWF models as well as the HAFS-A model deepening 90W as low as 890 hPa by the end of the forecast period. Although GDM infamously also rapidly strengthened Kalmaegi prior to reaching the Philippines only for it to make landfall at 90 kts, the trends with 90W are somewhat more concerning, especially with RIPA suggesting a high likelihood of rapid intensification during the next 72 hours.

The result of all this is a low-confidence track and intensity forecast that shows 90W going nowhere in particular during the next 5 days. At this point, it is too soon to say which areas - if any - could be affected by this system. The intensity forecast is also more aggressive than the JMA forecast and makes the system a major typhoon by the end of the period. Despite the aggressive forecast, it’s about in the middle of the guidance envelope.

Forecast positions and maximum winds

• 000 hrs: 8.1°N 147.8°E – 30 kts

• 012 hrs: 8.6°N 145.8°E – 30 kts

• 024 hrs: 9.3°N 143.9°E – 40 kts

• 048 hrs: 10.4°N 143.0°E – 55 kts 

• 072 hrs: 13.1°N 140.6°E – 70 kts 

• 096 hrs: 14.0°N 137.5°E – 85 kts

• 120 hrs: 15.6°N 133.9°E – 100 kts