WDPN31 PGTW 160900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (TWENTYTHREE) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.5N 123.5E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 155 NM EAST-NORTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW-LEVEL CIRCULATION CENTER WITH DEEP CONVECTIVE BANDING
WRAPPING INTO THE LOW-LEVEL CIRCULATION CENTER (LLCC) FROM THE
NORTHWEST AND SOUTHEASTERN QUADRANTS. A 160729Z F-18 SSMIS 91GHZ
MICROWAVE IMAGE HIGHLIGHT THE AFOREMENTIONED DEEP CONVECTIVE
BANDING AND SLIGHT VERTICAL TILT SOUTHEASTWARD DUE TO 5-10KTS OF
VERTICAL WIND SHEAR IMPACTING RELATIVELY SMALL TROPICAL DEPRESSION
(TD). THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
THE AFOREMENTIONED ANIMATED MSI AND MICROWAVE IMAGERY. THE INITIAL
INTENSITY OF 25 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN
EARLIER 160106Z METOP-B ASCAT SCATTEROMETRY IMAGE REVEALING A
PARTIAL BUT TIGHT WIND FIELD WITH 20-25KTS IN THE NORTHERN
PERIPHERY.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T1.0 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TD 23W WILL CONTINUE TO TRACK IN A
NORTHWESTWARD DIRECTION FOR THE NEXT 36 HOURS WHILE STEERED BY A
SUBTROPICAL RIDGE TO THE NORTHEAST. TOPOGRAPHIC INTERACTION IS
ANTICIPATED BETWEEN TAU 12-36 AS THE SYSTEM PASSES OVER LUZON. THE
LAND INTERACTION IS EXPECTED TO HINDER INTENSIFICATION DURING THAT
PERIOD. TD 23W WILL TRACK BACK OUT OVER WATER BY TAU 36, ALLOWING
FOR INTENSIFICATION TO RESUME IN FAVORABLE CONDITIONS OF LOW
VERTICAL WIND SHEAR, WARM SEA SURFACE TEMPERATURES, AND FAVORABLE
UPPER-LEVEL DIFFLUENCE. AN APPROACHING SUBTROPICAL RIDGE AT TAU 48
WILL BECOME THE PRIMARY STEERING INFLUENCE, AND DRIVE TD 23W TO A
WESTWARD TRACK BY TAU 72. TD 23W IS ANTICIPATED TO REACH A PEAK
INTENSITY OF 60KTS AT TAU 72. BETWEEN TAU 96-120, TD 23W IS
ANTICIPATED TO TRACK CLOSELY TO HONG KONG. WEAKENING WILL HAVE
BEGUN BY TAU 96 DUE TO LAND INTERACTION AND UPWELLING IN THE
SHALLOW COASTAL REGION. TD 23W WILL BE DISSIPATING OVER LAND BY THE
END OF THE FORECAST PERIOD. 

MODEL DISCUSSION: THE JTWC MULTI-MODEL GUIDANCE IS IN GOOD
AGREEMENT THAT TD 23W WILL CURVE NORTHWESTWARD, AND THEN WESTWARD
THROUGHOUT THE FORECAST PERIOD. HOWEVER, THERE ARE SEVERAL KEY
DIFFERENCES BETWEEN MODELS WHICH WILL INFLUENCE INTENSIFICATION,
AND AS A RESULT THE INTENSIFICATION GUIDANCE HAS A LARGER SPREAD.
OVER LUZON, GFS TRACKS LONGER OVER THE MOUNTAIN RANGE THAN ECMWF,
WHICH WOULD RESULT IN A LARGER HINDRANCE TO INTENSIFICATION. LATER
IN THE FORECAST, GFS AND HWRF REACHES A HIGHER PEAK
INTENSITY AND NEVER MAKES LANDFALL IN THE SOUTH CHINA SEA.
ALTERNATIVELY, HAFS-A AND ECMWF MAKE LANDFALL IN THE VICINITY OF
HONG KONG AND WEAKENS SIGNIFICANTLY WHILE APPROACHING THE COAST AND
AFTER LANDFALL. THE JTWC TRACK FORECAST LIES SLIGHTLY SOUTH OF THE
CONSENSUS MEAN, AND THE INTENSITY FORECAST LIES SLIGHTLY BELOW THE
CONSENSUS MEAN.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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