WDPN31 PGTW 151500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (SIXTEEN) 
WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.8N 154.4E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 557 NM EAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL DEPRESSION 16W (SIXTEEN) HAS ALMOST COMPLETELY DISSIPATED,
FROM A CONVECTIVE CLOUD SIGNATURE STANDPOINT, OVER THE PAST SIX
HOURS, FAILING TO OVERCOME PERSISTENT NORTHEASTERLY CONVERGENCE AND
MID-LEVEL DRY AIR INTRUDING FROM THE EAST. AT PRESENT, THERE IS NO
DISCERNABLE LOW LEVEL CIRCULATION CENTER (LLCC) IN THE ENHANCED
INFRARED SATELLITE IMAGERY, THOUGH A MID-LEVEL ROTATION IS EVIDENT
TO THE WEST OF THE ASSESSED LLCC. HENCE THE SYSTEM HAS BEEN
RELOCATED, WITH THE 151200Z POSITION IN ROUGHLY THE SAME POSITION
AS THE PREVIOUS 150600Z POSITION. THE ONLY SUPPORT TO THE LOW
CONFIDENCE INITIAL POSITION IS AN EXTRAPOLATION OF A 150800Z SSMIS
91 GHZ MICROWAVE SHOWING A VERY BROAD AND WEAK CIRCULATION AND A
150823Z SCATTEROMETER PASS WHICH SHOWED A VERY SMALL CIRCULATION AT
THE NORTHERN EXTREME OF A SHARP WAVE FEATURE. THE INITIAL INTENSITY
IS ASSESSED WITH LOW CONFIDENCE, AS BOTH PGTW AND KNES COULD NOT
LOCATE A CENTER TO FIX THIS CYCLE, AND ONLY RJTD PROVIDED A FIX.
THE PREVIOUS SCATTEROMETER PASS INDICATED MOSTLY 15-20 KNOT WINDS,
WITH ONE OR TWO 25 KNOT WINDS ABOUT 100 NM TO THE NORTHEAST. THE
UPPER-LEVEL, NORTH-SOUTH ORIENTED RIDGE AXIS REMAINS SOLIDLY
ENTRENCHED JUST EAST OF THE ASSESSED CENTER AND CONTINUES TO INDUCE
CONVERGENT FLOW ALOFT AND MID-LEVEL DRY AIR ENTRAINMENT, OFFSETTING
THE WEAK POLEWARD OUTFLOW.

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

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF THE DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T1.5 - 25 KTS
   CIMSS SATCON: 40 KTS AT 150819Z
   CIMSS ADT: 33 KTS AT 151140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE INITIAL POSITION HAS BEEN
RELOCATED AND THE FORECAST INTENSITY AT GUAM CPA HAS BEEN REDUCED
TO LESS THAN TROPICAL STORM STRENGTH. 

FORECAST DISCUSSION: WHILE THE EXACT CENTER POSITION OF TD 16W IS
VERY UNCERTAIN, THE WEAK LLCC WILL CONTINUE TO TRACK WESTWARD ALONG
THE SOUTHERN PERIPHERY OF THE VERY STRONG STR TO THE NORTH UNTIL IT
PASSES NEAR OR OVER THE ISLAND OF GUAM NEAR TAU 36. ONCE PAST GUAM,
THE SYSTEM WILL TURN ONTO A NORTHWESTWARD TRACK THROUGH THE
REMAINDER OF THE FORECAST, ALONG THE SOUTHWESTERN PERIPHERY OF THE
STR. TD 16W IS NOT EXPECTED TO INTENSIFY, AND MAY ACTUALLY WEAKEN
BELOW TROPICAL DEPRESSION STRENGTH IN THE NEAR TERM, AS MID-LEVEL
DRY AIR AND CONVERGENT NORTHEASTERLY FLOW ALOFT PERSIST THROUGH TAU
24. AS THE SYSTEM APPROACHES GUAM, THE UPPER-LEVEL RIDGE THAT HAS
PERSISTED FOR THE PAST TWO DAYS WILL BEGIN TO WEAKEN AND RECEDE
NORTHWARD, WEAKENING THE NORTHEASTERLY FLOW ALOFT, ALLOWING FOR
DEVELOPMENT OF SLIGHTLY IMPROVED SHEAR AND OUTFLOW CONDITIONS,
WHICH SHOULD ALLOW FOR A SMALL AMOUNT OF INTENSIFICATION TO 30
KNOTS PRIOR TO THE PASSAGE OVER GUAM. ONCE WEST OF GUAM, THE
ATMOSPHERE MOISTENS SIGNIFICANTLY, A POINT SOURCE AND RADIAL OUTFLOW
DEVELOP ALOFT, AND THE SYSTEM WILL BEGIN A PERIOD OF STEADY
INTENSIFICATION TO A PEAK OF 75 KNOTS BY TAU 120.  

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH THE
ENTIRE FORECAST PERIOD WITH A SPREAD OF 85 NM AT TAU 36 AS THE
SYSTEM PASSES GUAM, INCREASING TO 140 NM AT TAU 120. HOWEVER, THE
RECENT RELOCATION AND THE UNCERTAINTY IN THE INITIAL POSITION LENDS
LOW CONFIDENCE TO THE OVERALL TRACK FORECAST AND ADJUSTMENTS TO
BOTH THE CPA DISTANCE AND TIMING ARE POSSIBLE AS THE SYSTEM
APPROACHES GUAM. INTENSITY GUIDANCE ALSO REMAINS IN GOOD AGREEMENT
BUT IS ASSESSED AS OVERLY OPTIMISTIC, PARTICULARLY IN THE EXTENDED
FORECAST PERIOD, WITH HWRF FOR EXAMPLE INDICATING A RAPID
INTENSIFICATION AFTER TAU 72 TO A PEAK OF 135 KNOTS AT TAU 120. IN
ZERO TO 48 HOUR FORECAST HOWEVER, MOST OF THE GUIDANCE SHOWS A FLAT
OR VERY SLOW INTENSIFICATION TREND. THE JTWC FORECAST LIES JUST
BELOW THE GUIDANCE ENVELOPE THROUGH TAU 48, THEN CLOSELY TRACKS THE
SHIPS-GFS THEREAFTER, BELOW THE CONSENSUS MEAN THROUGH THE FORECAST
PERIOD. OVERALL, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST. 

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