Advisories

WDPN31 PGTW 242100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (IN-FA) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.1N 165.6E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 194 NM NORTHWEST OF KWAJALEIN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 30W WITH SYMMETRICALLY EXPANDING, BUT STILL
DISORGANIZED, DEEP CONVECTION THAT FULLY OBSCURES THE COMPACT
LOW-LEVEL CIRCULATION CENTER. THE 241718Z SSMIS MICROWAVE IMAGERY
REVEALS THE SYSTEM IS BECOMING MORE VERTICALLY STACKED, WITH A
SMALL PATCH OF LOW EMISSIVITY MARKING THE CENTER IN THE 37 GHZ
IMAGE AND A DISTINCT CURL OF CONVECTION WRAPPING INTO THE CORE IN
THE 91 GHZ IMAGE. ENVIRONMENTAL ANALYSIS REVEALS A FAVORABLE
ENVIRONMENT, CHARACTERIZED BY LOW TO MODERATE (15-20 KTS) VERTICAL
WIND SHEAR (VWS), WARM (28-29 C) SEA SURFACE TEMPERATURES (SST),
MODERATE (75-100 KJ PER CM SQUARED) OCEAN HEAT CONTENT (OHC), AND
MODERATE RADIAL OUTFLOW. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED SSMIS IMAGERY. THE INITIAL
INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK FIXES AND AUTOMATED CIMSS INTENSITY ESTIMATES LISTED
BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   PHFO: T3.0 - 45 KTS
   CIMSS SATCON: 52 KTS AT 241449Z
   CIMSS ADT: 47 KTS AT 241740Z
   CIMSS AIDT: 45 KTS AT 241740Z
   CIMSS D-MINT: 47 KTS AT 241526Z
   CIMSS D-PRINT: 52 KTS AT 241810Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 30W (IN-FA) HAS TRACKED NORTHWESTWARD AS
THE NEAR EQUATORIAL RIDGE (NER) TO ITS SOUTHEAST BEGINS TO BUILD.
THE SYSTEM REMAINS IN A WEAK STEERING ENVIRONMENT, BUT IS EXPECTED
TO CONTINUOUSLY ACCELERATE TO THE NORTHWEST AS THE NER BUILDS AND
GUIDES THE STORM THROUGH TAU 36. BY AROUND TAU 36, THE SUBTROPICAL
RIDGE (STR) TO THE NORTHWEST IS EXPECTED TO STRETCH TO THE EAST,
CAUSING A COMPETING STEERING ENVIRONMENT BETWEEN TAU 36-60. THE STR
IS EXPECTED TO GAIN STEERING AUTHORITY BY TAU 60, AND CAUSE 30W TO
TRACK WEST-NORTHWESTWARD THROUGH THE REMAINDER OF THE FORECAST
PERIOD. REGARDING INTENSITY, 30W IS FORECAST TO BEGIN A PERIOD OF
RAPID INTENSIFICATION (RI) IMMEDIATELY. 30W IS EXPECTED TO RI
THROUGH TAU 36, WHEN THE COMPETING STEERING ENVIRONMENT TEMPORARILY
HALTS INTENSIFICATION. 30W MAY ALSO BRIEFLY WEAKEN AROUND TAU
36-60. ONCE 30W TRANSITIONS STEERING ENVIRONMENTS AND BEGINS
TRACKING WEST-NORTHWESTWARD, IT WILL ENTER A REGION OF ELEVATED
(100-125 KJ PER CM SQUARED) OHC VALUES, SUPPORTING A SECOND ROUND
OF INTENSIFICATION. 30W IS EXPECTED TO PEAK AT TAU 120, THOUGH
ADDITIONAL INTENSIFICATION MAY OCCUR OUTSIDE THE FORECAST PERIOD. 

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN
MODERATE AGREEMENT THROUGH TAU 120, THOUGH THERE ARE A FEW OUTLIERS
(NAVGEM, GFS, GSM) THAT DEPICT 30W TRACKING NORTHEASTWARD FROM TAU
0-60 BEFORE LOOPING BACK TO THE WEST-NORTHWEST. DISREGARDING THOSE
MEMBERS, THE JTWC TRACK FORECAST LIES WITH THE BULK OF
PHYSICS-BASED MODEL GUIDANCE AND ALL EXPERIMENTAL AI MEMBERS WITH
OVERALL MEDIUM CONFIDENCE. RELIABLE INTENSITY AIDS ARE ALSO IN
MODERATE AGREEMENT THROUGH TAU 120. SEVERAL JTWC RI AIDS MEET
CRITERIA, HEAVILY SIGNALING THE POSSIBILITY OF RI FOR THE NEXT 36
HOURS. UNCERTAINTY EMERGES REGARDING THE INTENSITY FOLLOWING RI AND
THE INTENSITY AS 30W CHANGES STEERING INFLUENCES, WITH A FEW MODELS
DEPICTING A SLIGHT WEAKENING FROM TAU 36-60. FOLLOWING TAU 60, ALL
MODELS GENERALLY AGREE IN A PERIOD OF REINTENSIFICATION THROUGH TAU
120. THE JTWC INTENSITY FORECAST IS ASSESSED WITH OVERALL MEDIUM
CONFIDENCE AND IS IN GOOD AGREEMENT WITH HAFS-A, HWRF, COAMPS-TC,
AND GOOGLE DEEPMIND.

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