msgid/genadmin/navpacmetoccen Pearl Harbor hi/jtwc// subj/prognostic reasoning for typhoon 06w warning nr 27//rmks/ 1. For meteorologists. 2. 12 hour summary and analysis. A. Typhoon (TY) 06w (Nakri) has weakened gradually from 80 knots to 65 knots over the past 12 hours. TY 06w has begun extratropical transition as it has accelerated to the northeast at 21 knots. Vertical wind shear has increased and has started to adversely impact the system. Ocean heat content values have decreased significantly, aiding in the weakening of TY 06w. The system has tracked along the northwestern periphery of the sub- tropical steering ridge within the enhanced flow ahead of a midlatitude trough to the west. B. The current position is based on recent satellite fixes from pgtw and rjtd. Although TY 06w is no longer exhibiting an eye, the circulation remains well defined and therefore there is high confidence in the initial position. The current intensity estimate is consistent with Dvorak fix values of 4.0 from pgtw and 4.5 from rjtd. Deep convection associated with TY 06w is now almost solely displaced to the east of the low level circulation center due to the influence of increased westerly vertical wind shear. TY 06w is beginning to interact with the baroclinic zone to the west-northwest of the system. TY 06w continues to track northeastward along the western periphery of a subtropical steering ridge to the east of the system. 3. Forecast reasoning a. The forecast philosophy has changed slightly from the previous prognostic reasoning. Extratropical transition has commenced and is now forecast to be complete prior to tau 24. B. TY 06w will continue to track along the northwest periphery of the subtropical steering ridge to the east. This steering influence will continue to take the cyclone northeastward through tau 12 ahead of an approaching midlatitude trough located to the west of the system. TY 06w will track to the east-northeast after tau 12 as it continues to undergo extratropical transition. The numerical model vortex trackers are in good agreement with the current forecast track. TY 06w is expected to continue to weaken within the enhanced westerly flow ahead of the midlatitude trough. Increasing vertical wind shear, passage over cooler water, and the continued influx of cooler, drier air over the western portion of the circulation will result in a steady weakening of the system throughout the forecast period. These negative influences will lead to TY 06w becoming fully extratropical prior to tau 24. Forecast team: Bravo//