msgid/genadmin/navmarfcstcen Pearl Harbor hi/jtwc// subj/prognostic reasoning for tropical storm 16w warning nr 01// rmks/ 1. For meteorologists. 2. 12 hour summary and analysis. A. Animated multispectral satellite imagery indicates that the low- level circulation center (LLCC) has consolidated quickly over the past 06 hours with a persistent cluster of deep convection over the LLCC. A 092058z SSMI image depicts improved convective banding from the southwest quadrant wrapping into the northwest quadrant with a well- defined LLCC. Animated water vapor imagery shows enhanced outflow associated with a midlatitude shortwave trough propagating east of northern Japan and currently north of the system. B. Ts 16w is tracking west-northwestward under the steering influence of the low-level subtropical ridge (str) positioned north of the system. The current position is based on satellite position fixes showing a well-defined low-level circulation center (llcc) in multispectral satellite imagery. The current intensity is slightly higher than the Dvorak estimates of 30 knots from knes and pgtw, and is based more on a ship report within 60 nm of the center at 09/18z from 9hac8 reporting 010/30 knots plus the rapidly improving convective signature in microwave imagery. 3. Forecast reasoning a. This is the first warning on this system. B. Ts 16w is tracking west-northwestward under the steering influence of the low-level subtropical ridge (str) positioned north of the system. There is currently a weakness in the str north of the systm, however, the midlatitude shortwave trough associated with it is tracking northeastward away from the system and is unlikely to initiate a re-curve. As the trough shifts northeast, the str is forecast to build north of the system further reinforcing the westward track through tau 36-48. Another shortwave is forecast to track into the east sea by tau 36 and will allow the system to re- curve east of Tokyo. Extra-tropical transition will begin around tau 36 as the system begins to interact with the trough and ts 16w is forecast to complete extra-tropical transition by tau 72. Model guidance is limited but supports the current track. The system is forecast to intensify at 10 knots per day through tau 36 due to favorable SST and outflow but will encounter increasing vertical wind shear near Japan that will weaken the system. Forecast team: Charlie//