Western Pacific Tropical Analysis: July 16, 2017

After a surge in the Southwest Monsoon, Severe Tropical Storm Talas has managed to develop in the South China Sea and headlines the Tropical Western Pacific. After skirting Hainan, the system is headed for a north-central Vietnam landfall, and Talas brings the threat for heavy rainfall along its track as it moves inland. Talas is the only system to monitor in the near term, but there are some signs in the medium range that the Southwest Monsoon may extend back across The Philippines, reestablishing the monsoon trough in the Philippine Sea in late July.

***NOTE: While I would consider myself well-learned in meteorology, I am still a student with more to learn before becoming a degreed meteorologist. This forecast is not from an official source and should not be treated as such. For official information, please refer to your local weather agency.***

As mentioned, Severe Tropical Storm Talas is currently the center of attention in the basin. As of 12Z, Talas was positioned at 18.5*N, 107.2*E. This is along the southern edge of the Gulf of Tonkin, and closing in on the north-central Vietnam shoreline. 50 kt is the consensus intensity estimate from both JMA and JTWC at the time.

Talas has strengthened more than I had expected thus far. I was skeptical it would gain enough organization to become classified in the days leading up to its development, but persistent convective activity near the vorticity maximum allowed the system to properly consolidate and become a named system while in the open water of the South China Sea. Since that time, Talas has managed to steadily strengthen up to the time of this post. As of 06Z July 16, Talas even managed to meet JMA’s 50 kt severe tropical storm threshold, the intensity it still carries as of the most recent 12Z analysis. However, time has just about run out for Talas, and the system will be making landfall on the Vietnam coastline in a matter of hours. Heavy rainfall is the greatest threat Talas carries with it as it moves inland across Southeast Asia.

Elsewhere across the Tropical Western Pacific, conditions remain generally hostile for tropical cyclone development. The tropical upper tropospheric trough (TUTT) remains oriented east/west along 20*N across much of the basin, and a breakoff TUTT low is currently traversing westwards across the Philippine Sea. Mid-level heights also remain higher than usual, indicating subsidence from the upper levels remains an issue. However, arguably the biggest issue that currently is plaguing the basin is the lack of low level equatorial westerlies extending east across the basin. These westerlies, associated with the Southwest Monsoon, are essential for establishing the monsoon trough, from which the vast majority of basin activity originates. Without these monsoon westerlies/southwesterlies, and by extension the monsoon trough, it becomes much more difficult to get tropical cyclogenesis, even with otherwise favorable conditions.

In the near term, not much is expected to change across the Tropical Western Pacific. However, guidance appears to be trying to bring the monsoon trough back in the medium range. Beginning in about seven days, ensemble means extend the monsoon southweserlies back across the Philippines and into the Philippine Sea. It’s too early to be confident in any type of tropical cyclogenesis around that period, but coupled with falling mid-level heights, conditions appear to be trending towards more favorable conditions towards the end of July.

My next entry will likely arrive by Wednesday. Until the next entry is posted, analyses and updates in forecast philosophy will arrive in the comments section.


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