msgid/genadmin/navpacmetoccen Pearl Harbor hi/jtwc// subj/prognostic reasoning for tropical storm 06w warning nr 05// rmks/ 1. For meteorologists. 2. 12 hour summary and analysis. A. Tropical Storm (TS) 06w (Nakri) has steadily intensified while tracking generally poleward along the western periphery of a subtropical steering ridge over the past 12 hours. A low level eye feature evident in a 272041z coriolis microwave satellite image indicates definitive improvement in the low level structure. Recent animated water vapor satellite imagery shows enhanced poleward outflow ahead of a midlatitude trough to the northeast of the storm as well as improving equatorward outflow. B. The current storm position is based on satellite fixes from pgtw and rjtd and the previously-mentioned 272041z coriolis image. The current intensity is consistent with Dvorak intensity estimates of 3.5 from both pgtw and rjtd. Ts 06w is entering a fairly weak steering environment among an extensive subtropical ridge to the east, weak low to mid-level ridging to the west, and a developing ridge to the north. Ts 06w lies beneath an upper level anticyclone in a region of low vertical wind shear and favorable diffluence aloft. Ocean heat content is also quite high. 3. Forecast reasoning a. The forecast track has been shifted slighly westward in response to changes in the anticipated steering flow. Forecast intensities have been increased slightly due to favorable upper level support and changes to the forecast track that carry the cyclone over warm water for a longer period. B. Ts 06w is expected to turn gradually northwestward over the next 24 hours as low to mid-level ridging builds in the wake of a mid-latitude trough on the poleward side of the storm. The upper level reflection of this ridging will likely suppress poleward outflow from ts 06w. However, good equatorward outflow, low vertical wind shear, and favorably high ocean heat content will allow ts 06w to intensify steadily before reaching a peak intensity around tau 72. The storm will track slowly northwest- Ward through tau 48 under the weak steering influence of the building ridge to the north. As a midlatitude trough approaches from the northwest this ridge will weaken, allowing the cyclone to recurve poleward between tau 48 and tau 72. C. Ts 06w will turn northeastward and accelerate ahead of the developing midlatitude trough in the extended period. Increasing vertical wind shear and the introduction of cooler and drier air into the tropical cyclone circulation will induce both steady weakening and extratropical transition beginning around tau 96 and continuing through tau 120. Forecast team: Alpha// nnnn