wdpn31 pgtw 271500 msgid/genadmin/navpacmetoccen Pearl Harbor hi/jtwc// subj/prognostic reasoning for tropical storm 22w warning nr 04// rmks/ 1. For meteorologists. 2. Prognostic reasoning for 271200z Oct to 011200z Nov 2006. A. Tropical Storm (TS) 22w (Cimaron), located approximately 540 nm east of Manila, Philippines, has tracked west-northwestward at 08 knots over the past six hours. B. Ts 22w continues to track west-northwestward along the south- western periphery of a subtropical ridge anchored east of Taiwan and this general track is expected to continue through tau 48. An approaching midlatitude trough currently over central China will induce a weakness in the steering ridge between tau 24 and tau 36. However, this trough is not expected to extend far enough Equator- Ward to capture ts 22w into the mid-latitude flow. A ridge building over eastern China in the wake of this trough will become the primary steering mechanism for ts 22w after tau 48 and is expected to flatten the storm track to nearly due west as the storm crosses central Luzon. The available dynamic aids are in good agreement with this scenario with the exception of MM5, which depicts a pole- Ward track after tau 24 in response to an over-developed weakness in the steering ridge. This forecast is based on a consensus of all available dynamic aids with less emphasis on the MM5 scenario. C. Ts 22w is expected to intensify at a climatological rate through tau 24 under the influence of low vertical wind shear and good radial outflow. Passage of the approaching trough currently to the northwest of the system is expected to introduce slightly drier, more stable air in its wake and hold intensification of the system to a less than climatological rate after tau 24. Interaction with land will weaken the system slightly between tau 48 and tau 72. D. Current wind radii are based on convective signature and climatology for an average-sized system. Forecast wind radii are based on climatology for an average-sized system. E. In the extended Taus, ts 22w is expected to weaken steadily in the South China Sea as a low level cold surge of drier north- easterly flow establishes over the South China Sea. The strength of this cold surge will largely determine the extent to which ts 22w weakens as it progresses. A weaker surge would allow the storm to maintain a higher intensity and continue to press westward under the influence of mid-level ridging to the north. A weaker storm would be steered at a lower level, on a more southwestward track. This forecast considers a strong cold surge and corresponding weakening of the system as forecast by most of the available numerical models, and therefore depicts a steady turn toward the southwest through tau 120. Forecast team: Bravo//