Tropical Storm Bailu (13W) – Tropical Cyclone Advisory #4: 0000 UTC 3 August 2025

…Depression passing southeast of Japan becomes Tropical Storm Bailu…

Current storm information:

• Position: 33.2°N 140.9°E

• Movement: NNE at 16 knots (25 km/h)

• Intensity: 35 knots (65 km/h)

• Central pressure: 995 hPa

Trend:

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

Discussion:

Convection associated with Tropical Depression 13W has increased in coverage during the past 12 hours or so, with some persistent clusters of convection present in the western semicircle. The circulation itself has become better defined, although it remains somewhat elongated from southwest to northeast due to being located within an upper-level trough extending from the northeast (which is actually noted as a frontal boundary on NWS OPC surface analysis). The intensity is increased to 35 kts, based primarily on surface observations and scatterometer data, and JMA has upgraded it to Tropical Storm Bailu.

Bailu is expected to move quickly toward the northeast as it rounds a strong subtropical ridge to the southeast. Although the environment appears to be favorable for strengthening with low shear and warm-ish SSTs, Bailu’s fast forward motion and general lack of organization will probably preclude any significant increases in strength, and in fact no strengthening is forecast through the end of the forecast period. By Tuesday, Bailu should become embedded within the same baroclinic zone currently causing Krosa to undergo extratropical transition, and Bailu too will likely become post-tropical by Wednesday as it races toward the Date Line.

Forecast positions and maximum winds

• 00 hrs: 33.2°N 140.9°E – 35 kts

• 12 hrs: 35.8°N 144.6°E – 35 kts

• 24 hrs: 37.0°N 148.9°E – 35 kts

• 48 hrs: 37.4°N 156.2°E – 35 kts

• 72 hrs: 39.4°N 160.4°E – 30 kts

• 96 hrs: 43.1°N 166.4°E – 30 kts Post-tropical/extratropical

• 120 hrs: 44.5°N 178.0°W – 30 kts Post-tropical/extratropical