WDPN32 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (CHABA) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.0N 115.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 329 NM WEST-NORTHWEST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH SPIRAL BANDS OF
DEEP CONVECTION WRAPPING IN FROM THE SOUTHWEST. A PARTIAL 300232Z
METOP-B ASCAT IMAGE REVEALS A COMPACT WIND FIELD COMPRISED OF 30 KNOT 
WINDS TO THE SOUTH OF THE LLCC WITH A SMALL REGION OF 35 KNOT WINDS. 
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON MSI AND 
ASCAT IMAGERY. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON ASCAT IMAGERY AND AGENCY DVORAK INTENSITY
ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 40 KTS AT 300302Z
   CIMSS ADT: 41 KTS AT 300540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 04W (CHABA) IS FORECAST TO TRACK
NORTH-NORTHWESTWARD AND EVENTUALLY NORTHWESTWARD IN A FAVORABLE
ENVIRONMENT BEFORE MAKING LANDFALL NEAR THE LUICHOW PENINSULA.
ENVIRONMENTAL CONDITIONS ARE FORECAST TO REMAIN FAVORABLE
CHARACTERIZED BY WARM SEA SURFACE TEMPERATURES (SST) (30C), MODERATE
DIVERGENCE ALOFT AND LOW-MODERATE VERTICAL WIND SHEAR (11-18 KNOTS)
WHICH WILL ALLOW CHABA TO REACH A MAXIMUM INTENSITY OF 65 KNOTS BY
TAU 48. BETWEEN TAU 48 AND TAU 72 CHABA WILL BEGIN TO INTERACT WITH
BOTH THE ISLAND OF HAINAN AND EVENTUALLY MAINLAND CHINA SIGNIFICANTLY 
IMPACTING INTENSITY AS THE SYSTEM BEGINS TO TRACK NORTH-
NORTHWESTWARD. BETWEEN TAU 72 AND TAU 96 TC 04W WILL STEADY UP ON AN 
APPROXIMATE NORTHWARD TRACK AS IT CONTINUES TO SUCCUMB TO THE 
OROGRAPHIC IMPACTS OF SOUTHERN CHINA BEFORE FINALLY DISSIPATING NEAR 
TAU 120.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT THROUGH
TAU 48 WITH ONLY A 100NM SPREAD IN THE SOLUTIONS. PAST TAU 48 AVNI
TAKES AN UNREALISTIC ABRUPT TURN WESTWARD WHILE THE BULK OF THE
GUIDANCE CONTINUES THE SYSTEM NORTHEASTWARD AND MODEL SPREAD
INCREASES TO 160NM, FOR THIS REASON JTWC FORECAST TRACK IS PLACED
WITH MEDIUM CONFIDENCE. RELIABLE INTENSITY GUIDANCE IS IN GOOD
AGREEMENT WITH ALL MEMBERS SHOWING A STEADY INTENSIFICATION THROUGH
TAU 48 AFTER WHICH LANDFALL OCCURS AND A SHARP DECREASE IN INTENSITY 
IS REFLECTED. THERE IS A POSSIBILITY FOR A MORE DRAMATIC 
INTENSIFICATION TREND THROUGH TAU 48 WITH A BULK OF THE MODELS
DISAGREEING ON THE EXTENT OF THIS INTENSIFICATION TREND THUS JTWC 
INTENSITY FORECAST IS PLACED WITH MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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