WDPN31 PGTW 260900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 33W (KOTO) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.9N 116.4E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 532 NM EAST-SOUTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 33W (KOTO) WITH VIGOROUS BURSTS OF DEEP CONVECTION OVER THE
CENTER AND PROMINENT CONVECTIVE BANDING ALONG THE NORTHERN AND
SOUTHERN PERIPHERIES. AS THE SYSTEM CONTINUES TO MERGE WITH THE
NORTHEASTERLY SURGE, GALE-FORCE WIND RADII ARE RAPIDLY EXPANDING,
PARTICULARLY WITHIN THE NORTHERN SEMICIRCLE. A TIMELY 260558Z GMI
37 GHZ MICROWAVE IMAGE REVEALED A DEFINED MICROWAVE EYE FEATURE,
ALLOWING THE INITIAL POSITION TO BE PLACED WITH HIGH CONFIDENCE.
THE INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY DVORAK AND CIMSS OBJECTIVE ESTIMATES LISTED
BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 33W IS IN A FAVORABLE
ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD AND EQUATORWARD
OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (28-29
C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: 260145Z METOP-B SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: PLACED WITHIN A WEAK STEERING
ENVIRONMENT BETWEEN RIDGING TO BOTH THE EAST AND WEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T3.5 - 55 KTS
   CIMSS SATCON: 51 KTS AT 260602Z
   CIMSS ADT: 59 KTS AT 260430Z
   CIMSS AIDT: 51 KTS AT 260430Z
   CIMSS D-PRINT: 48 KTS AT 260430Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 33W IS FORECAST TO TRACK GENERALLY WESTWARD
THROUGH TAU 48 WITH STEADILY DECREASING TRACK SPEEDS AS THE SYSTEM
TRACKS FURTHER INTO AN AREA OF WEAK STEERING INFLUENCE. AFTER TAU
48, A SLOW NORTHWESTWARD MOVEMENT IS FORECAST THROUGH TAU 96 AS
RIDGING OVER NORTHERN PHILIPPINES BUILDS BACK IN TO THE EAST OF THE
VORTEX. AFTER TAU 96, RIDGING OVER SOUTHEAST ASIA WILL BECOME THE
PRIMARY STEERING MECHANISM, CAUSING 33W TO TRACK WESTWARD TOWARD
THE COAST OF VIETNAM THROUGH TAU 120. REGARDING INTENSITY, 33W IS
FORECAST TO INTENSIFY THROUGH TAU 24 TO A PEAK OF AROUND 70 KTS AS
THE ENVIRONMENT REMAINS RELATIVELY FAVORABLE. HOWEVER, NEAR TAU 24,
SHEAR BEGINS TO QUICKLY INCREASE TO AROUND 25-30 KTS FROM THE
SOUTH. THIS SHEAR, ALONG WITH DRY AIR ENTRAINMENT ASSOCIATED WITH
THE NORTHEASTERLY SURGE, WILL CAUSE 33W TO WEAKEN THROUGH TAU 72.
AFTER TAU 72, SHEAR AND DRY AIR ARE EXPECTED TO LESSEN AS THE SURGE
BEGINS TO RETREAT, ALLOWING 33W TO GRADUALLY REDEVELOP AS IT
APPROACHES THE COAST OF VIETNAM. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 48 WITH AN 85 NM CROSS-TRACK SPREAD AT THAT
TIME. SPREAD THEN RAPIDLY INCREASES AFTERWARD AS MODELS DIFFER IN
INTERACTION WITH THE WEAK STEERING ENVIRONMENT. GFS IS A BIT OF AN
OUTLIER, STALLING THE SYSTEM FROM TAU 48-96. EGRR AND AFUM BOTH
TURN THE SYSTEM NORTHWARD MUCH EARLIER AND ECMWF KEEPS A MORE
WESTWARD TRAJECTORY. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE
MULTI-MODEL CONSENSUS THROUGH TAU 48, THEN MORE IN LINE WITH THE
GDM AND EC-AIFS SOLUTIONS WITH MEDIUM CONFIDENCE THROUGH TAU 72 AND
LOW CONFIDENCE THEREAFTER. INTENSITY GUIDANCE IS SLIGHTLY SPLIT IN
THE NEAR TERM, WITH HAFS-A, HWRF, AND RAPID INTENSIFICATION (RI)
AIDS SUGGESTING A PEAK OF AROUND 75-90 KTS AT TAU 24. THE REMAINDER
OF GUIDANCE IS IN THE 60-70 KNOT RANGE AT THE SAME TIME PERIOD.
AFTER TAU 24, MODELS AGREE ON WEAKENING THROUGH TAU 72. AFTER TAU
72, GFS IS AN OUTLIER IN QUICKLY INTENSIFYING THE SYSTEM, WHILE ALL
OTHER MODELS SUGGEST EITHER CONTINUED WEAKENING OR A STEADY
INTENSITY. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE
HAFS-A MODEL AND SLIGHTLY HIGHER THAN THE CONSENSUS WITH OVERALL
MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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