Tropical Depression 20W (Julian) 2024
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Live tracking map, satellite images and forecasts of Tropical Depression 20W 2024 in the Philippine Sea. Current wind speed 45km/h. Max 215km/h.
20W (Philippine name Julian) is located 706 km south-southwest of Kadena Air Base, and has tracked south-southwestward at 15 km/h (8 knots) over the past 6 hours. Maximum significant wave height is 3.7 meters (12 feet).
For the next 24 hours, the primary steering mechanism for 20W will remain the subtropical ridge to the west, centered south of Hong Kong.
The ridge however is not expected to remain stationary but rather will quickly exit stage right and move into northern Vietnam, allowing 20W to track southwestward over the next 24 hours.
After 24 hours, the system moves into a weak steering pattern, caught between a large subtropical ridge complex over southern China, an extension of the subtropical ridge extending along a line from Mindanao through Guam and troughing to north over Korea.
So for the 24 hours in 1 to 2 days, the system will very slowly drift westward as the various ridges jostle for dominance. In 2 days, the subtropical ridge extension to the southeast is forecast to break off into a discrete anticyclone, and start moving northward while continuing to build.
After 2 days, this new ridge center will become the dominant steering influence, pushing 20W onto a generally northward track through the remainder of the forecast period.
Late in the forecast period, the exact position of the ridge center relative to 20W will have a major impact on the track forecast after 4 days.
The further east the center, the further east the track and vice versa. The current forecast keeps the center east of Taiwan but skirts the eastern coast at a relatively close range.
In terms of intensity, the system is going to enjoy favorable conditions for the bulk of the forecast period. In the near-term, intensification will be relatively slow as the system continues to consolidate and the wind field symmetrizes.
The pace of intensification is expected to pick up in earnest after 36 hours, as by this point the circulation is fully formed, it is moving slowly over the highest ocean heat content along the track and the anticyclone aloft becomes intense, with the system expected to reach typhoon strength in 2 days, if not sooner. But this is just setting the stage for the real fireworks, which commence at 2 days.
Rapid intensification (IR) is forecast in 2 to 3 days, followed by near-RI up to 4 days, when the system is expected to peak at or near 215 km/h (115 knots).
Interaction with Taiwan, and increased shear will result in modest weakening in 5 days. One factor that may influence the peak intensity is moderate to high mid-level shear, which the GFS in particular is predicting to impact the system in around 3 days.
The deterministic GFS intensity guidance picks up on this and peaks the system at about 175 km/h (95 knots). Deterministic track guidance is in fairly good agreement on the overall track scenario.
All of the guidance shows a southwest track, then slow westward movement, followed by an ejection to the north in 2 days. There is however a modest amount of cross-track spread in 3 days, with the GALWEM splitting off from the pack and driving the system over the babuyan islands, while the GFS, GEFS and ECMWF turn the system more sharply northward, leading to a 361 km spread at 3 days.
Cross-track spread continues to increase such that in 5 days, it reaches 611 km between GALWEM near Kaohsiung, Taiwan, and the GEFS west of Kadena.
The JTWC forecast lies just inside the consensus mean over the next 3 days, then aligns well with the interpolated GFS and ECMWF over the next 5 days.
Intensity guidance is in strong agreement on the intensification trend over the next 3 days, before the models split with the AHNI peaking at 175 km/h (95 knots), while the HAFS-A peaks at 230 km/h (125 knots).
The JTWC forecast generally follows the consensus mean but peaks about 20 km/h (10 knots) higher than the mean.
The GEFS and ECENS ensemble have come into better agreement now, with both means keeping the system east of Taiwan, though there remains a relatively large spread covering roughly the Taiwan Strait to Ishigakijima.