msgid/genadmin/navpacmetoccen Pearl Harbor hi/jtwc// subj/prognostic reasoning for typhoon 06w warning nr 17// rmks/ 1. For meteorologists. 2. 12 hour summary and analysis. A. Typhoon (TY) 06w (Nakri) has taken a poleward turn and weakened significantly from an estimated intensity of 11o knots to 80 knots over the past 12 hours. Forward track speed has slowed to 04 knots as the storm progresses through its turn. B. The current position is based on recent satellite fixes from pgtw and rjtd. While a defined eye feature is no longer evident in multispectral and water vapor satellite imagery, the center remains sufficiently evident to lend good confidence to the current position esimate. The current intensity estimate is consistent with dvorak fix values of 4.5 from both pgtw and rjtd. Moderate northerly vertical wind shear induced by the peripheral flow around a synoptic scale anticyclone aloft has driven the recent weakening trend and exposed much of the northern portion of the low level circulation center. The cyclone is turning poleward along the western periphery of a subtropical steering ridge extension to the northeast. 3. Forecast reasoning a. The forecast philosophy remains largely unchanged from the previous warning. However, forecast intensities have been reduced in response to the recent steady weakening trend and the forecast track has been shifted slightly poleward in the medium to long term to reflect the expectation of a broader recurvature. B. TY 06w will proceed increasingly poleward and eventually north- eastward as it tracks around the western periphery of the subtropical steering ridge ahead of a developing midlatitude trough over the next 72 hours. As TY 06w encounters strengthening flow ahead of the mid- latitude trough around tau 48, it will begin an along-track acceler- ation. Persistent northerly vertical wind shear in the near term and both increasing westerly vertical wind shear and decreasing ocean heat content in the medium to long term portion of the forecast are expected to steadily weaken TY 06w through tau 72. Interaction with the approaching midlatitude trough, including the increase in vert- ical wind shear and introduction of cooler and drier air to the western portion of the cyclone circulation, will induce the first stage of extratropical transition around tau 48. C. TY 06w will become fully embedded in the midlatitude flow pattern ahead of the developing trough in the extended forecast period. The storm is expected to weaken slowly as it completes the transition into an extratropical low during this period. Forecast team: Alpha//