msgid/genadmin/navpacmetoccen Pearl Harbor hi/jtwc// subj/prognostic reasoning for super typhoon 13w warning nr12// rmks/ 1. For meteorologists. 2. 12 hour summary and analysis. A. The system was upgraded on the previous warning to super typhoon (sty) status and has essentially maintained a 130-135 knot intensity over the past 06-12 hours. The system has continued to track west-northwestward and passed just south of ishigaki jima (47918) near 17/21-22z. Hourly surface observations indicated Max sustained winds (10-minute average) of 64 knots gusting to 88 knots and minimum slp of 951mb. The models have remained consistent over the past 24 hours and are in good agreement with a re-curve scenario into the central korean peninsula. B. The current position is based on a well-defined 20-nm small round eye with a tight cluster of satellite and radar position fixes, therefore, there is high confidence in positioning and the 12-hour motion. The current intensity is based on Dvorak intensity estimates ranging from 127 to 140 knots. Sty 13w continues to track under the steering influence of the deep subtropical ridge situated north of the system. A. Forecast intensity after tau 36 and the timing of extra- tropical transition (et) was significantly changed from the 17/12z warning. Reasoning will be explained fully below. B. Recent upper level analysis indicate a mid-level subtropical ridge (str) situated north of the system with a high centered near 30n 140e. The ridge extends westward into the Shanghai region with a weakness located near 28n 117e. The western periphery of the str is forecast to weaken with the approach of a strong midlatitude trough and allow the system to re-curve into the Yellow Sea. This trough is currently deepening over eastern China, along 110e and is moving eastward at 10-15 knots. Sty 13w is forecast to gradually turn northwestward over the next 12 hours and will make landfall south of Shanghai. The system will rapidly weaken due to interaction with land but will also begin extra-tropical transition between tau 24 and tau 36 as it encounters midlatitude westerlies associated with the aforementioned trough and increasing vertical wind shear. Sty 13w is forecast to enter the Yellow Sea after tau 36 as a 50- 55 knot system but is not expected to re-intensify due to significantly cooler SST near 23-24c as well as stronger vertical wind shear. Sty 13w should complete et prior to making landfall over the korean peninsula but is expected to accelerate and maintain as a strong extra-tropical low with strong resultant winds.