Advisories

WDPN31 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.1N 149.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 317 NM NORTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
PERSISTENT DEEP CONVECTION CONFINED TO THE SOUTHERN PERIPHERY OF
THE COMPACT LOW-LEVEL CIRCULATION CENTER (LLCC). OVER THE PAST SIX
HOURS, THE LOW-LEVEL CLOUD LINES ALONG THE EASTERN SIDE HAVE
ACCELERATED, SUGGESTING IMPROVED LOW-LEVEL ROTATION. A 121108Z
ASCAT-B PASS REVEALS AN OBLONG, CLOSED WIND FIELD WITH A PATCH OF
25-30 KT WINDS IN THE SOUTHERN SEMICIRCLE. TROPICAL DEPRESSION (TD)
28W HAS BECOME BETTER ORGANIZED WHILE TRAVERSING WARM SEA SURFACE
TEMPERATURES (SST) OF 28-29 DEGREES CELSIUS IN AN OTHERWISE
MARGINAL ENVIRONMENT OF DRY AIR AND NORTHERLY VERTICAL WIND SHEAR
(VWS) OF 15-20 KTS, LARGELY ASSOCIATED WITH A TROPICAL
UPPER-TROPOSPHERIC TROUGH (TUTT) JUST TO THE WEST. BASED ON THE
SLIGHT IMPROVEMENT IN STORM STRUCTURE AND THE SCATTEROMETER DATA,
THE INITIAL INTENSITY IS RAISED TO 30 KTS WITH HIGH CONFIDENCE. THE
INITIAL POSITION IS ALSO PLACED WITH HIGH CONFIDENCE BASED ON
EXTRAPOLATION OF THE ASCAT-B DATA AND THE PARTIALLY EXPOSED LLCC IN
SHORTWAVE IR IMAGERY.

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

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A LOW- TO
MID-LEVEL SUBTROPICAL RIDGE (STR) CENTERED NEAR 28N 165E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.0 - 25 KTS
   CIMSS ADT: 33 KTS AT 121140Z
   CIMSS AIDT: 27 KTS AT 121140Z
   CIMSS D-MINT: 28 KTS AT 121150Z
   CIMSS D-PRINT: 31 KTS AT 121140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK EQUATORWARD
   OTHER FACTORS: EXTENSIVE DRY AIR

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TD 28W WILL CONTINUE TO TRACK GENERALLY
NORTHWESTWARD ALONG THE SOUTHWESTERN FLANK OF A LOW- TO MID-LEVEL
STR. SIGNIFICANT INTENSIFICATION APPEARS UNLIKELY. MARGINAL
ENVIRONMENTAL CONDITIONS, CONSISTING OF EXTENSIVE DRY AIR AND
MODERATE VWS, WILL PERSIST AND LIMIT FURTHER DEVELOPMENT.
CONCURRENTLY, THE TUTT WILL PASS OVER THE SYSTEM DURING THE NEXT
12-24 HOURS. THIS MAY SUPPRESS VERTICAL MOTION AND LIMIT
UPPER-LEVEL OUTFLOW. IF THE SYSTEM PERSISTS PAST TAU 36, THE
SHALLOW VORTEX WILL APPROACH A SHEAR LINE ORIENTED FROM THE
SOUTHWEST TO THE NORTHEAST. THIS FEATURE WILL DISRUPT THE LOW-LEVEL
CIRCULATION, CAUSING TD 28W TO DEGENERATE INTO A TROUGH. THE SYSTEM
COULD DISSIPATE BEFORE TAU 48.

MODEL DISCUSSION: TRACK GUIDANCE HAS COME INTO MUCH BETTER
AGREEMENT, WITH THE CROSS-TRACK SPREAD DECREASING FROM 65 NM LAST
CYCLE TO 30 NM THIS CYCLE AT TAU 24. THE ALONG-TRACK SPREAD IS ALSO
LOW. BOTH THE DYNAMICAL AND AI MODELS ARE CLUSTERED WITHIN THE
TIGHT GUIDANCE ENVELOPE. THE JTWC FORECAST TRACK IS POSITIONED WITH
HIGH CONFIDENCE ALONG THE NORTHERN SIDE OF THE ENVELOPE, ALIGNING
WITH THE DEEPMIND, ECMWF, AND GFS SOLUTIONS. MODEST SPREAD EXISTS
AMONG THE INTENSITY AIDS. COAMPS-TC DEPICTS ADDITIONAL
INTENSIFICATION TO 35 KTS BY TAU 12, FOLLOWED BY A SLOW WEAKENING
TREND. DEEPMIND, HAFS-A, AND GFS HOLD THE INTENSITY THROUGH TAU 12,
FOLLOWED BY GRADUAL WEAKENING. THE JTWC INTENSITY FORECAST REFLECTS
THE LATTER SCENARIO WITH HIGH CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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