Tropical Storm NORU Advisory Do, 22.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 17.7N 134.7E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 530 NM NORTH-NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: EASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS PERSISTENT
DEEP CONVECTION WRAPPING INTO A DEEP CONVECTIVE CLOUD STRUCTURE
OBSCURING A LOW LEVEL CIRCULATION CENTER (LLCC). A 212138Z SSMIS 91
GHZ MICROWAVE IMAGE DEPICTS SHALLOW BANDING WRAPPING INTO A LOW
LEVEL CIRCULATION CENTER. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE ANIMATED MULTISPECTRAL IMAGERY WHICH SHOWS
A WELL DEFINED LOW LEVEL CIRCULATION ALONG WITH A BULLSEYE 220011Z
METOP-B ASCAT. THE INITIAL INTENSITY IS PLACED WITH HIGH CONFIDENCE
BASED ON THE AFOREMENTIONED 220011Z METOP-B ASCAT, WHICH SHOWS UP
TO 30 KNOTS WRAPPING AROUND THE SOUTHERN PERIPHERY OF THE SYSTEM
ALONG WITH AGENCY DVORAK INTENSITY ESTIMATES, PGTW T1.5 AND KNES
T1.5.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK RADIAL
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.
FORECAST DISCUSSION: TD 18W IS CURRENTLY IN A QUASI-STATIONARY
MOTION DUE TO A WEAK SYNOPTIC STEERING PATTERN, AS THE SYSTEM HAS
BEGUN TO SLOW ITS EASTWARD MOTION OVER THE PAST 6 HOURS. AS THE
DEEP-LAYER SUBTROPICAL RIDGE TO THE NORTHEAST BEGINS TO BUILD AND
TAKE OVER AS THE DOMINATE STEERING FEATURE, TD 18W WILL BEGIN TO
TURN SHARPLY TO THE NORTHWEST. AFTER TAU 12, THE SYSTEM WILL
CONTINUE IN A WESTWARD DIRECTION WHILE SLOWLY INTENSIFYING UP TO 40
KNOTS TAU 72. THE FORECAST CALLS FOR GRADUAL STRENGTHENING DUE TO
MARGINALLY FAVORABLE CONDITIONS CHARACTERIZED BY WARM SEA SURFACE
TEMPERATURES (SSTS) (29-30C), MODERATE VERTICAL WIND SHEAR
(10-15 KNOTS) AND WEAK RADIAL OUTFLOW. ADDITIONALLY, GFS MODELED
700MB-300MB RELATIVE HUMIDITY VALUES ARE FORECAST TO BE LOW
SURROUNDING THE SYSTEM AS IT MOVES WESTWARD. AFTER TAU 72, TD 18W
WILL MAKE LANDFALL IN LUZON, WHICH WILL THEN RESULT IN A DECREASE
IN INTENSITY DUE TO THE BRIEF LAND INTERACTION. BETWEEN TAU 96 AND
TAU 120, 18W WILL MOVE BACK OVER WATER INTO THE SOUTH CHINA SEA
CONTINUING TO TRANSIT WESTWARD THROUGHOUT THE FORECAST.
MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL FAIR AGREEMENT
THAT 18W WILL TURN SHARPLY TO THE NORTHWEST WITHIN THE NEXT 12 HOURS
AND CONTINUE ON A WESTWARD TRACK BEFORE MAKING LANDFALL AFTER TAU 72.
AFTER TAU 72, THE GUIDANCE BEGINS TO SPREAD AS UNCERTAINTY
INCREASES IN BOTH CROSS TRACK AND ALONG TRACK VARIABILITY THROUGH
THE END OF THE FORECAST. THE JTWC TRACK FORECAST IS PLACED WITH
MEDIUM CONFIDENCE THROUGH TAU 72, THEN LOW CONFIDENCE FROM TAU 96
TO TAU 120. INTENSITY GUIDANCE SHOWS HIGH SPREAD AND UNCERTAINLY IN
POSSIBLE SOLUTIONS. THEREFORE, THE JTWC INTENSITY FORECAST IS
PLACED WITH LOW CONFIDENCE
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
NNNN
NNNN