msgid/genadmin/navmarfcstcen Pearl Harbor hi/jtwc// subj/prognostic reasoning for tropical depression 21w warning nr 12// rmks/ 1. For meteorologists. 2. 12 hour summary and analysis. A. The system has continued to struggle after its passage over the Philippines and was downgraded to a tropical depression (td) on the 01/18z warning. Animated satellite imagery depicts poorly- organized deep convection with no clear consolidating low-level circulation center (LLCC). A 012034z AMSU image depicts a weak, elongated LLCC with limited banding over the southern semi-circle and weaker curved banding north. The system appears to be track- ing westward slowly but there is a high degree of uncertainty in positioning due to the disorganized state. The models have remained inconsistent except for GFDN, NOGAPS and ECMWF. B. TD 21w is tracking westward under the steering influence of the low- to mid-level subtropical ridge (str) positioned north of the system. The recent 500mb analysis confirmed strong ridging, supporting a continued short-term westward track. Animated water vapor imagery depicts weak equatorward outflow and almost non- xistent poleward which is hindered by convergent flow north of the system and a lack of a poleward outflow channel. The current position is based on animated multispectral satellite imagery along with a 012257z SSMI image which depicts a weak LLCC. The current intensity is based on Dvorak estimates ranging from 30 to 35 knots and is assessed lower due to the poor organization. 3. Forecast reasoning. A. No changes to the forecast philosophy over the past 24 hours. B. TD 21w is forecast to strengthen and track westward to west- northwestward under the steering ridge through tau 48. The str is forecast to erode ahead of an approaching midlatitude shortwave trough allowing the system to turn poleward by tau 72. Most of the dynamic models have been very inconsistent after tau 48 with minor differences in the strength of the str. Additionally, tc-laps remains the sole outlier with a very unrealistic track northward, perpendicular to the ridge. The remainder of the models are in fair agreement through tau 72. GFDN, ECMWF and NOGAPS have remained very consistent with tracks close to hong kong. The other model solutions have varied significantly and have indicated additional problems handling/initializing the weak system. TD 21w is forecast to slowly intensify under marginal conditions through tau 24 then at a 10-15 knot per day rate through tau 72. Intensity guidance supports a peak intensity ranging from 55-65 knots in general. C. In the extended period, TD 21w is forecast to make landfall near Hong Kong and to dissipate over land by tau 120. Model guidance is in fair agreement. Forecast team: Delta//