WDPN32 PGTW 180300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (MAN-YI) WARNING NR 037//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.0N 118.1E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 575 NM EAST-NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 25W
(MAN-YI) WITH A WELL-DEFINED, PARTIALLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) AND SPARSE CONVECTION BEGINNING TO FORM
OVER THE CENTER. A 172201Z F17 SSMIS 37 GHZ MICROWAVE IMAGE REVEALS
THAT THE STRUCTURE OF THE LOWER LEVELS REMAINS STRONG AS THE
VORTEX ATTEMPTS TO RECOVER FROM LANDFALL OVER LUZON. ENVIRONMENTAL
ANALYSIS INDICATES THAT 25W IS IN A MARGINALLY FAVORABLE
ENVIRONMENT CHARACTERIZED BY MODERATE RADIAL OUTFLOW ALOFT, LOW TO
MODERATE (15-20 KTS) VERTICAL WIND SHEAR, AND WARM (28-29 C) SEA
SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE TIGHTLY WRAPPING LOW-LEVEL CLOUDS IN THE
ANIMATED MSI. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED WITH LOW
CONFIDENCE DUE TO THE WIDE RANGE BETWEEN AGENCY DVORAK AND
OBJECTIVE INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF AN EXTENSION OF A
SUBTROPICAL RIDGE (STR) TO THE EAST THAT EXTENDS WESTWARD, NORTH OF
THE SYSTEM.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T5.0 - 90 KTS
   KNES: T5.0 - 90 KTS
   CIMSS ADT: 94 KTS AT 180000Z
   CIMSS AIDT: 71 KTS AT 180000Z
   CIMSS DPRINT: 50 KTS AT 180000Z
   CIMSS DMINT: 52 KTS AT 172204Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: PRESSURE FROM THE COLD SURGE FLOWING
SOUTHWESTWARD INTO THE SOUTH CHINA SEA.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 25W IS FORECAST TO CONTINUE TRACKING
WEST-NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF RIDGING TO THE
NORTH THROUGH TAU 12. THE COLD SURGE FLOWING INTO THE SOUTH CHINA
SEA ALONG WITH THE MENTIONED RIDGING WILL INHIBIT 25W FROM GAINING
MUCH LATITUDE. FROM TAU 12 TO 24, 25W IS FORECAST TO TRACK
GENERALLY WESTWARD. AFTER TAU 24, THE SYSTEM IS EXPECTED TO TURN
WEST-SOUTHWESTWARD AS THE WEAKENED VORTEX TRACKS ALONG THE LOW-LEVEL
STEERING PATTERN. 25W WILL THEN FOLLOW THAT TRACK THROUGH THE
REMAINDER OF THE FORECAST WITH DISSIPATION AROUND TAU 72. REGARDING
INTENSITY, 25W IS FORECAST TO STEADILY WEAKEN TO AROUND 30 KTS AT
TAU 48 AS THE SYSTEM TRAVERSES WESTWARD ACROSS THE SOUTH CHINA SEA.
THE TWO MAIN CAUSES OF THE WEAKENING TREND IS HIGH WESTERLY
VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT, AIDED BY THE COLD
SURGE WHICH WILL BRING IN COLD, DRY AIR TOWARDS THE SYSTEM. NEAR
TAU 48, THE ENVIRONMENT WILL QUICKLY WORSEN AS SIGNIFICANT AMOUNTS
OF DRY AIR ENTRAINS INTO THE VORTEX AND SHEAR INCREASES TO OVER 35
KTS. AS A RESULT, 25W IS FORECAST TO RAPIDLY WEAKEN AFTERWARD WITH
DISSIPATION NO LATER THAN TAU 72.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING THE TRACK OF 25W THROUGH TAU 48 WITH THE EXCEPTION OF
GALWEM, WHICH TRACKS THE VORTEX MUCH FARTHER SOUTHWARD THAN THE
REMAINDER OF GUIDANCE. DISREGARDING GALWEM, THERE IS A 110 NM
CROSS-TRACK SPREAD AT TAU 48. AFTER TAU 48, MODELS QUICKLY BEGIN TO
DIFFER DUE TO THE RAPIDLY WEAKENING SYSTEM, SOME MODELS EVEN LOSE
THE VORTEX AROUND TAU 60. THE JTWC TRACK FORECAST IS PLACED CLOSE
TO THE CONSENSUS, DISREGARDING GALWEM, THROUGHOUT THE FORECAST WITH
HIGH CONFIDENCE THROUGH TAU 48 AND LOW CONFIDENCE THEREAFTER.
INTENSITY GUIDANCE IS IN MODERATE AGREEMENT, WITH ALL MODELS
SUGGESTING A WEAKENING TREND STARTING AT TAU 0. THE JTWC INTENSITY
FORECAST IS PLACED CLOSE TO CONSENSUS WITH OVERALL MEDIUM
CONFIDENCE.

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