Tropical Storm LAN Advisory dom, 15.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 25W (TWENTYFIVE)
WARNING NR 01//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 25W (TWENTYFIVE), LOCATED APPROXIMATELY 78 NM
WEST OF YAP, FSM, HAS TRACKED WEST-NORTHWESTWARD AT 06 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS
THE SYSTEM HAS IMPROVED AS FORMATIVE CONVECTIVE BANDS, ALBEIT STILL
SHALLOW, HAVE BECOME MORE ORGANIZED AND SYMMETRICALLY WRAPPED INTO A
DEFINED LOW LEVEL CIRCULATION CENTER. THE INITIAL POSITION LINED UP
WELL WITH A LOW REFLECTIVITY CIRCULATION FEATURE IN THE 150922Z SSMIS
MICROWAVE PASS. THE INITIAL INTENSITY OF 25 KNOTS IS CONSISTENT WITH
DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD. UPPER LEVEL ANALYSIS
INDICATES THE SYSTEM IS IN AN AREA OF LOW (05-10 KNOT) VERTICAL WIND
SHEAR AND MODERATE RADIAL OUTFLOW THAT IS PROVIDING ADEQUATE
VENTILATION TO THE CENTRAL CONVECTION. ALONG-TRACK SEA SURFACE
TEMPERATURES IN THE PHILIPPINE SEA ARE 30 DEG CELSIUS AND ALSO
FAVORABLE FOR DEVELOPMENT. THE CYCLONE IS CURRENTLY TRACKING WITH THE
LOW LEVEL EASTERLY TRADEWIND FLOW.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING BULLETIN ON THIS
SYSTEM AND SETS THE FORECAST PHILOSOPHY.
   B. NEAR TERM, TD 25W WILL GRADUALLY TRACK ON A MORE NORTHWESTWARD
TRAJECTORY AS A NEAR EQUATORIAL RIDGE TO THE EAST EMERGES AS THE
INITIAL STEERING MECHANISM. HOWEVER, AFTER TAU 24, A MID-LEVEL
REFLECTION OF THE SUBTROPICAL RIDGE (STR) TO THE NORTHEAST WILL
ASSUME STEERING AND DRIVE THE CYCLONE ON A MORE WESTWARD TRACK. AFTER
TAU 36, THE STR WILL WEAKEN AND RECEDE, ALLOWING TD 25W TO TRACK MORE
POLEWARD. THE FAVORABLE DYNAMICS MENTIONED IN PARA 2 WILL PERSIST AND
PROMOTE A FASTER THAN NORMAL INTENSIFICATION; BY TAU 72 THE SYSTEM
WILL BE A MODERATE TYPHOON AT 90 KNOTS CENTRAL WIND SPEED.
   C. AFTER TAU 72, TD 25W WILL CONTINUE ITS NORTHWARD TRACK UNDER
THE STEERING INFLUENCE OF THE STR AND MAY LIKELY UNDERGO RAPID
INTENSIFICATION AS FAVORABLE CONDITIONS FURTHER IMPROVE INCLUDING
INCREASED POLEWARD OUTFLOW. THE SYSTEM IS EXPECTED TO REACH 110 KNOTS
CENTRAL WIND SPEED BY END OF FORECAST, POSSIBLY HIGHER. THE AVAILABLE
NUMERIC GUIDANCE, TYPICAL WITH DEVELOPING SYSTEMS, IS IN POOR
AGREEMENT AS INDICATED IN THE WIDE SPREAD IN THE MODEL ENVELOPE. IN
VIEW OF THIS, THERE IS LOW CONFIDENCE IN THE INITIAL JTWC TRACK
FORECAST ON TD 25W.//
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