WDPN31 PGTW 160900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (SIXTEEN) 
WARNING NR 024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.6N 149.8E
   INITIAL INTENSITY: 20 KTS
   GEOGRAPHIC REFERENCE: 286 NM EAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL DEPRESSION 16W HAS CONTINUED TO DETERIORATE, AND IS NOW
ASSESSED AS BEING BELOW JTWC WARNING INTENSITY. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS THE BROAD OUTLINES OF
THE GENERAL CIRCULATION, THOUGH AT PRESENT THERE IS NO DISCREET LOW
LEVEL CIRCULATION CENTER (LLCC) EVIDENT IN AVAILABLE IMAGERY. THERE
ARE MULTIPLE SMALL CENTERS OF ROTATION (SPINNERS) TRACKING TO THE
NORTHWEST ALONG THE NORTHEAST PERIPHERY OF THE LARGER CIRCULATION
CENTER BUT THESE ARE NOT ASSESSED AS THE CENTER OF THE SYSTEM. A
160557Z SSMIS 91 GHZ MICROWAVE IMAGE DEPICTED SCATTERED CONVECTION
DEVELOPING IN A LINEAR BAND TO THE WEST AND SOUTH OF THE ASSESSED
LLCC, AND HELPED REFINE THE INITIAL POSITION. HOWEVER, WITH THE
BROAD NATURE OF THE SYSTEM AND THE PRESENCE OF MULTIPLE SPINNERS,
THERE IS LOW CONFIDENCE IN THE INITIAL POSITION. THE INITIAL
INTENSITY IS LOWERED TO 20 KNOTS, WITH MEDIUM CONFIDENCE. NO
AGENCIES ARE CURRENTLY PROVIDING AN INTENSITY FIX, AND THE REDUCED
INTENSITY IS BASED PRIMARILY ON A 152150Z ASCAT-A PASS WHICH SHOWED
A MAXIMUM OF 20-24 KNOT WINDS DISPLACED WELL TO THE NORTH OF THE
CENTER, WITH ONLY 10-15 KNOTS ELSEWHERE. ANALYSIS OF THE VISIBLE
AND WATER VAPOR IMAGERY SHOWS THE AXIS OF THE UPPER-LEVEL RIDGE
LIES DIRECTLY OVER TOP OF THE LLCC, WITH CIRRUS BLOWOFF MOVING
SOUTHWARD ALONG THE EAST SIDE, AND WEST-NORTHWESTWARD ON THE WEST
SIDE. THE PRESENCE OF FLARING CONVECTION ON THE WEST SIDE AND
LITTLE TO NO CONVECTION TO THE EAST SUPPORTS THE PRESENCE OF THIS
INVERTED RIDGE, WITH CONVERGENCE AND DRY AIR TO THE EAST AND
DIVERGENT, MOIST FLOW ON THE WEST.

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

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   CIMSS ADT: 35 KTS AT 160250Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK WESTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE INITIAL INTENSITY HAS BEEN
LOWERED TO BELOW JTWC WARNING CRITERIA AND THE FORECAST TRACK HAS
BEEN MOVED TO THE NORTH OF GUAM. 

FORECAST DISCUSSION: WHILE THE INITIAL INTENSITY HAS BEEN REDUCED
TO BELOW THE JTWC WARNING THRESHOLD, THE SYSTEM IS FORECASTED TO
REGAIN TROPICAL STORM STRENGTH WITHIN THE NEXT 48 HOURS AND THUS
WARNINGS WILL CONTINUE TO BE ISSUED. TD 16W IS FORECAST TO TRACK
GENERALLY WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE STEERING
RIDGE THROUGH TAU 24, THEN TURN NORTHWESTWARD THROUGH THE REMAINDER
OF THE FORECAST SOUTHWEST PERIPHERY OF THE STR AS IT REORIENTS.
WHILE THERE IS NO CHANGE IN THE OVERALL TRACK PHILOSOPHY OR
STEERING MECHANISM, THE RECENT TRACK MOTION HAS BEEN
WEST-NORTHWEST, STEADILY GAINING LATITUDE OVER THE PAST 24 HOURS,
AND THUS THE FORECAST TRACK NOW TAKES THE SYSTEM SLIGHTLY TO THE
NORTH OF GUAM. THE LATEST ANIMATED VISIBLE IMAGERY INDICATES THE
SYSTEM MAY BE TURNING ONTO A MORE WESTWARD TRACK, BUT IT REMAINS
POSSIBLE THAT ADDITIONAL NORTHWARD ADJUSTMENT OF THE TRACK COULD BE
NECESSARY. DUE TO THE PRESENCE OF THE PERSISTENT MODERATE SHEAR, DRY
AIR ABOVE 500 MB AND UPPER-LEVEL MASS CONVERGENCE, THE SYSTEM HAS
CONTINUED TO WEAKEN OVER THE PAST 12 HOURS. OVER THE NEXT 24 HOURS
THE UPPER-LEVEL CONDITIONS ARE EXPECTED TO BEGIN TO IMPROVE,
REDUCING SHEAR AND INCREASING OUTFLOW, WHICH WILL ALLOW FOR THE
SYSTEM TO BEGIN A STEADY INTENSIFICATION TREND THROUGH THE
REMAINDER OF THE FORECAST, PEAKING AT 75 KNOTS AT TAU 120.  

MODEL DISCUSSION: TRACK GUIDANCE IS IN RELATIVELY GOOD AGREEMENT
THROUGH TAU 72, WITH THE MAJORITY OF THE CONSENSUS MEMBERS TIGHTLY
PACKED WITH A PASSAGE JUST NORTH OF GUAM PRIOR TO TAU 24.
THEREAFTER MODEL SPREAD INCREASES TO A MODEST 130 NM AT TAU 72. IN
THE EXTENDED TAUS, MODEL SPREAD INCREASES FURTHER WITH A GROUP
CONSISTING OF NAVGEM, COAMPS-TC (GFS AND NAVGEM), GALWEM AND THE
ECMWF ENSEMBLE MEAN TAKING A MORE POLEWARD TRACK, WHILE THE GFS,
GFS ENSEMBLE MEAN, UKMET ENSEMBLE MEAN AND ECMWF TAKE THE TRACK
MORE EQUATORWARD. THE JTWC FORECAST FAVORS THE SOUTHERN GROUPING,
CONSISTENT WITH THE PREVIOUS FORECASTS. OVERALL CONFIDENCE IS
MEDIUM THROUGH TAU 72 IN LIGHT OF THE UNCERTAINTY OF THE INITIAL
POSITION AND TRACK, AND LOW CONFIDENCE THROUGH TAU 120. INTENSITY
GUIDANCE IS IN GOOD AGREEMENT ON THE SCENARIO, WITH LITTLE TO NO
INTENSIFICATION THROUGH TAU 24, THEN STEADY INTENSIFICATION
THEREAFTER. THE JTWC FORECAST MATCHES THE SHAPE OF THE CONSENSUS
MEAN, BUT REMAINS A BIT MORE CONSERVATIVE, WITH MEDIUM CONFIDENCE. 
 

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