Western Pacific Tropical Analysis: August 9, 2017

After about two and a half weeks, the Noru saga has come to a close at last. In the wake of the prolifically long lived typhoon, not much is left to be discussed as the basin has gone back into its slumber. Upper level subsidence has once again spread over the basin, and the monsoon southwesterlies have retracted back towards Southeast Asia, leaving little available focus for tropical development. The next period of significant tropical development is likely 10-14 days down the road, but as we approach the seasonal activity peak, it will become more and more difficult to keep down at least weak development for an extended period of time.

One coherent disturbance does currently exist over the Tropical Western Pacific. Located well to the east at approximately 14ºN, 174ºE, the disturbance features decent vorticity but lacking convective activity. The area this disturbance is traversing features high 500 mb heights and may be struggling with large scale subsidence. Considering the system’s present consolidation, tropical cyclogenesis cannot be ruled out with the system as it moves northwest and then north into a slight weakness between subtropical ridging, but subsidence and then shear north of 20ºN will likely prevent the disturbance from meeting requirements for a classifiable tropical cyclone. The system will likely be tagged as an invest, however.

Aside from the aforementioned disturbance, it is rather difficult to identify something with tropical cyclone potential over the next week or so. The belt of monsoon southwesterlies associated with last week’s reverse-oriented monsoon trough is now very far north and in the process of cutting off from the parent southwest monsoon. Large scale subsidence has also returned to the Tropical Western Pacific, and 500 mb heights are once again running abnormally high. Overall, conditions do not look favorable for tropical development.

In the medium range, there are some early hints that the monsoon trough may re-establish itself in the basin as subsidence begins to relax a little. Most guidance except American guidance show low level westerlies returning around day 10. I wouldn’t get hung up on American guidance failing to show a similar solution either, since it appears it gets Madden-Julian caught up in the Western Hemisphere, keeping a powerful downward pulse over the Tropical Western Pacific. This is a well-known bias in American guidance. Taking this into account, I’d say chances are rather good that the monsoon trough will make a return to the Philippine Sea, perhaps kicking off the next wave of activity around day 10.

Apologies for the missed post this past weekend as I was feeling rather poor. My next post is slated for this weekend. Until the next entry is posted, analyses and updates in forecast philosophy will arrive in the comments section.


One thought on “Western Pacific Tropical Analysis: August 9, 2017”

  1. The disturbance I mentioned has now been designated a Tropical Depression by JMA and 14W by JTWC. On a related note, it appears that I have been a bit too bearish in general towards tropical cyclogenesis so far this season.


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