WDPN32 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (CHABA) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.0N 113.6E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 201 NM SOUTH OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS WELL-DEFINED
SPIRAL BANDING FEATURES WRAPPING INTO A WELL DEFINED LOW LEVEL
CIRCULATION CENTER (LLCC). WHILE NO VISIBLE EYE IS YET PRESENT, A
010522Z AMSR2 89 GHZ MICROWAVE IMAGE DEPICTED FORMATIVE BANDING
WRAPPING INTO A WELL-DEFINED LLCC. ADDITIONALLY THE 36GHZ IMAGE
DEPICTED A NASCENT MICROWAVE EYE FEATURE. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON 36GHZ MICROWAVE EYE FEATURE,
ALONG WITH MULTI- AGENCY POSITION FIXES. THE INITIAL INTENSITY OF
55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE IMPROVING
CONVECTIVE STRUCTURE AS WELL AS A COMBINATION OF AGENCY DVORAK
INTENSITY ESTIMATES AND OBJECTIVE ADT AND SATCON ESTIMATES.
ENVIRONMENTAL CONDITIONS ARE FAVORABLE WITH WARM SSTS (29-30C), LOW
(10-15 KTS) EASTERLY VWS AND MODERATE TO STRONG EQUATORWARD
OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A MID TO
UPPER-LEVEL SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 59 KTS AT 010604Z
   CIMSS ADT: 59 KTS AT 010540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 04W (CHABA) IS FORECAST TO CONTINUE TRACK
NORTHWESTWARD, BEING PUSHED TOWARDS THE CHINESE COAST BY THE STR
CENTER CURRENTLY OVER THE NORTHERN PHILIPPINES. TRACK SPEED HAS
SLOWED SLIGHTLY AS A MID-LEVEL RIDGE HAS BUILT IN TO THE NORTH OF
THE SYSTEM OVER SOUTHERN CHINA. THIS IS EXPECTED TO WEAKEN OVER THE
NEXT 24 HOURS AND NOT INHIBIT THE GENERAL NORTHWESTWARD MOVEMENT.
THE SYSTEM IS FORECAST TO MAKE LANDFALL ALONG THE CHINESE COAST
SHORTLY AFTER TAU 24. AS THE RIDGE TO THE NORTH BREAKS DOWN, THE
SYSTEM WILL THEN CURVE POLEWARD AS IT CONTINUES TO WEAKEN. THE
SYSTEM IS FORECAST TO CONTINUE TO INTENSIFY STEADILY TO A PEAK OF
70 KNOTS PRIOR TO LANDFALL, UNDER FAVORABLE CONDITIONS OF WARM
SSTS, LOW SHEAR AND STRONG EQUATORWARD OUTFLOW. WHILE NOT
SPECIFICALLY FORECAST AT THIS TIME, THERE EXISTS A LOW PROBABILITY
OF RAPID INTENSIFICATION AS THE SYSTEM APPROACHES LANDFALL DUE TO
INCREASED OCEAN HEAT CONTENT IN THE SHALLOW COASTAL WATERS. ONCE
ASHORE, THE SYSTEM WILL RAPIDLY WEAKEN DUE TO LAND INTERACTION,
ULTIMATELY DISSIPATING NO LATER THAN TAU 72 OVER SOUTH-CENTRAL
CHINA. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT ON THE
NORTHWEST TRACK, WITH A SPREAD OF LESS THAN 50NM AT LANDFALL. THE
GUIDANCE ENVELOPE WIDENS SHARPLY AFTER LANDFALL AS THE SYSTEM
WEAKENS AND DISSIPATES, BUT ALL MODELS GENERALLY AGREE ON A TURN 
POLEWARD AFTER LANDFALL. THE JTWC FORECAST TRACK REMAINS CONSISTENT
WITH PREVIOUS FORECAST AND LIES CLOSE THE MULTI-MODEL CONSENSUS
MEAN WITH HIGH CONFIDENCE THROUGH TAU 24, DECREASING TO LOW, AND
MEDIUM OVERALL. INTENSITY GUIDANCE IS MIXED, WITH THE HWRF
INDICATING WEAKENING FROM TAU 00, WHILE THE REMAINDER OF THE
GUIDANCE INDICATES A SMALL AMOUNT OF INTENSIFICATION. HOWEVER,
RAPID INTENSIFICATION GUIDANCE IS TRIGGERING, WITH A PEAK OF 70
KNOTS PRIOR TO LANDFALL. THE JTWC FORECAST LIES ON THE RIPA
GUIDANCE THROUGH TAU 234, THEN CLOSELY TRACKS CONSENSUS MEAN
THEREAFTER. OVERALL CONFIDENCE IS MEDIUM THROUGH FORECAST PERIOD. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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