Advisories

WDPN31 PGTW 120900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.8N 149.8E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 339 NM NORTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) THAT HAS BECOME BETTER
DEFINED OVER THE PAST 12 HOURS. MSI AND A 120228Z AMSR3 89 GHZ
IMAGE SHOW DEEP CONVECTION CONFINED PRIMARILY TO THE SOUTHERN
PERIPHERY. A TROPICAL UPPER-TROPOSPHERIC TROUGH (TUTT) TO THE WEST
OF TROPICAL DEPRESSION (TD) 28W IS INDUCING NORTHERLY VERTICAL WIND
SHEAR (VWS) OF 10-15 KTS. THE SYSTEM IS EMBEDDED IN AN AREA OF DRY
AIR, WHICH LIMITS CONVECTIVE ACTIVITY. WHILE SEA SURFACE
TEMPERATURES (SST) ARE VERY WARM NEAR 29 DEGREES CELSIUS, THE
COMBINED EFFECTS OF DRY AIR AND SHEAR CREATE A MARGINAL ENVIRONMENT
FOR FURTHER INTENSIFICATION. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE IMPROVED DEFINITION OF THE EXPOSED
LLCC. THE INITIAL INTENSITY IS HELD AT 25 KTS WITH MEDIUM
CONFIDENCE BASED ON THE T1.0-1.5 DVORAK FIXES FROM RJTD AND PGTW.
THIS ASSESSMENT IS SLIGHTLY BELOW OBJECTIVE INTENSITY ESTIMATES
FROM CIMSS RANGING FROM 27 KTS TO 31 KTS.

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: T1.5 - 25 KTS
   RJTD: T1.0 - 25 KTS
   CIMSS ADT: 27 KTS AT 120540Z
   CIMSS AIDT: 27 KTS AT 120540Z
   CIMSS D-MINT: 30 KTS AT 120339Z
   CIMSS D-PRINT: 28 KTS AT 120540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: EXTENSIVE DRY AIR

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 NORTHWESTWARD
ALONG THE SOUTHWESTERN PERIPHERY OF A LOW- TO MID-LEVEL STR
POSITIONED TO THE NORTHEAST THROUGH TAU 48. THE NORTHERN PERIPHERY
OF THE AFOREMENTIONED TUTT WILL MOVE OVER THE SYSTEM BY TAU 12,
THEN SHIFT WEST OF THE SYSTEM BY TAU 24. THE TUTT WILL INDUCE
NORTHERLY SHEAR AND SUPPRESS VERTICAL MOTION OVER THE NEXT 24
HOURS. CONCURRENTLY, TD 28W WILL REMAIN EMBEDDED IN AN AREA OF
EXTENSIVE DRY AIR. THESE FACTORS WILL LIMIT CONVECTIVE ACTIVITY
DESPITE VERY WARM SST. AFTER TAU 24, AN UPPER-LEVEL RIDGE WILL
BUILD WESTWARD AND SHIFT THE VWS FROM NORTHERLY TO SOUTHERLY. THE
PERSISTENT SHEAR AND DRY AIR THROUGHOUT THE FORECAST PERIOD WILL
PRECLUDE SIGNIFICANT INTENSIFICATION. THE FORECAST CALLS FOR TD 28W
TO DEGENERATE INTO A TROUGH BY TAU 48, ALTHOUGH THIS COULD HAPPEN
SOONER.

MODEL DISCUSSION: THE TRACK GUIDANCE ENVELOPE IS RELATIVELY TIGHT,
MEASURING 95 NM AT TAU 48, WITH THE AI-GEFS ENSEMBLE MEAN BOUNDING
THE EQUATORWARD SIDE OF THE ENVELOPE AND GFS ON THE POLEWARD SIDE.
GOOGLE DEEPMIND, ECMWF, AND HAFS-A ARE TIGHTLY CLUSTERED NEAR THE
MULTI-MODEL CONSENSUS. THE JTWC FORECAST TRACK IS VERY SIMILAR TO
THE PREVIOUS FORECAST AND IS PLACED ALONG THIS CORE GROUP OF MODELS
WITH HIGH CONFIDENCE. GREATER SPREAD EXISTS AMONG THE INTENSITY
GUIDANCE. HAFS-A INTENSIFIES THE SYSTEM TO 30 KTS AND HOLDS THAT
INTENSITY WELL BEYOND TAU 48. DEEPMIND AND GFS KEEP A STEADY
INTENSITY THROUGH TAU 36 BEFORE WEAKENING THE SYSTEM TO 20 KTS NEAR
TAU 48. THE JTWC INTENSITY FORECAST LEANS TOWARD THE WEAKER
SCENARIO WITH MEDIUM CONFIDENCE.

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