Tropical Depression 05W (Bising) - Tropical Cyclone Advisory #1, 0000 UTC 7/4/25

…Tropical depression forms west of the Babuyan Islands… …Forecast to strengthen quickly…

Current storm information:

• Position: 20.0°N 118.9°E

• Movement: Nearly stationary

• Intensity: 30 knots (55 km/h)

• Central pressure: 1001 hPa

Trend:

• Steady to rapid strengthening is expected during the next 24 hours, and the depression will likely become a tropical storm later today.

Watches and warnings:

• TCWS #1: Calayan, Dalupiri, and northwestern Ilocos Norte

• The No. 1 standby signal is active for Hong Kong and Macau.

• Interests in Taiwan and southeastern China, as well as the Yaeyama Islands and Okinawa, should monitor the progress of TD 05W.

Hazards affecting land:

• The depression is currently producing areas of heavy rainfall over portions of northern and western Luzon, and this rainfall will likely spread inland over Luzon beginning on Saturday evening, followed by over the Batanes and Babuyan Islands and Taiwan on Sunday. This rain will likely cause severe flooding. In addition, destructive winds are possible in Taiwan on Monday. For additional details, including possible warnings, refer to products from your local weather office.

Discussion:

What a difference a few hours makes. The low pressure area near the western entrance of the Luzon Strait has very quickly gotten its act together, and it has attained enough organization to be considered a tropical depression. Convection has increased substantially in coverage and has already coalesced into a central overcast feature, with a large equatorward outflow band feeding into the monsoon trough to the south. The circulation center is partially exposed on the northeastern edge of the convection, although the center has gradually begun to become obscured. The intensity is a potentially conservative 30 kts, hedged between Dvorak estimates ranging from T1.5 to T2.5 as well as a D-PRINT estimate of 31 kts.

TD 05W is moving fairly little right now due to being stuck in a rather complicated steering regime consisting of a ridge to the north, a ridge over the Philippine Sea, and southwesterly monsoon flow to the south. This is greatly complicating the forecast, and JMA, JTWC, and some of the model guidance have wildly different track solutions once a trough moves in and causes 05W to begin moving northward on Saturday. The JTWC track shows a rather unusual track northeastward into the Taiwan Strait, while the JMA track shows 05W eventually making landfall in Taiwan and stalling out in the East China Sea. Most of the model guidance, including the GFS and ECMWF ensembles, show tracks east of Taiwan, with a few ensemble members sending 05W as far east as Okinawa by the end of the forecast period. The forecast positions below do not match either JTWC or JMA and attempt to average all the possible scenarios, but there is very low confidence in the track forecast.

The intensity forecast is also of low confidence. 05W is organizing quickly, and the CIMSS AI-RI guidance suggests a decent likelihood of rapid intensification. The environment is a bit better than marginally favorable, and some steady strengthening appears likely with 05W becoming a tropical storm later today. How much more strengthening occurs is dependent on how much interaction occurs with Taiwan - the weird JTWC track over the Taiwan Strait or the averaged track given below have much less interaction and therefore a stronger system. It is very possible that 05W could become a typhoon before even reaching Taiwan, and the averaged forecast indicates this.

Forecast positions and maximum winds

• 00 hrs: 20.0°N 118.9°E – 30 kts

• 12 hrs: 20.3°N 119.0°E – 40 kts

• 24 hrs: 20.7°N 119.9°E – 50 kts

• 48 hrs: 21.5°N 121.5°E – 65 kts

• 72 hrs: 23.5°N 123.2°E – 75 kts

• 96 hrs: 25.4°N 124.0°E – 80 kts

• 120 hrs: 26.5°N 123.5°E – 80 kts