Advisories

WDPN31 PGTW 230900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 25W (TWENTYFIVE) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.0N 138.4E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 373 NM NORTH OF ULITHI
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 25W AS A HIGHLY ELLIPTICAL LOW-LEVEL CIRCULATION
CENTER PARTIALLY OBSCURED BY PERSISTENT DEEP CONVECTION TO THE
NORTH. 25W HAS BECOME SLIGHTLY BETTER ORGANIZED OVER THE PAST
SEVERAL HOURS AND VERTICAL ALIGNMENT APPEARS TO BE IMPROVING. AN
EXPANDING PLUME OF DEEP CONVECTION HAS RECENTLY FORMED DIRECTLY
OVER THE CENTER, FURTHER INDICATING CONSOLIDATION. CLOUD TOPS WITHIN 
THAT PLUME ARE QUICKLY COOLING, DROPPING TO LESS THAN -80C IN JUST A 
FEW HOURS. ENVIRONMENTAL ANALYSIS REVEALS A HIGHLY FAVORABLE
ENVIRONMENT, CHARACTERIZED BY LOW (10-15 KTS) VERTICAL WIND SHEAR
(VWS), VERY WARM (29-30 C) SEA SURFACE TEMPERATURES (SST), HIGH
(100-120 KJ PER CM SQUARED) OCEAN HEAT CONTENT (OHC), STRONG
POLEWARD OUTFLOW, AND AMPLE MOISTURE THROUGHOUT THE AIR COLUMN. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
PARTIALLY EXPOSED LLCC. THE INITIAL INTENSITY OF 25 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE DPRINT ESTIMATE OF 27 KTS, PGTW
DVORAK FIX AT 1.5, AND THE IMPROVED APPEARANCE IN ANIMATED MSI.

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

CURRENT STEERING MECHANISM: A DEEP-LAYER SUBTROPICAL RIDGE CENTERED
TO THE NORTH-NORTHEAST OF THE SYSTEM

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   CIMSS D-PRINT: 27 KTS AT 230600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TD 25W IS FORECAST TO TRACK GENERALLY
NORTHWESTWARD WHILE IT REMAINS UNDER THE STEERING INFLUENCE OF THE
DEEP-LAYER STR CURRENTLY CENTERED TO ITS NORTH-NORTHEAST. 25W IS
EXPECTED TO MAINTAIN A RELATIVELY CONSISTENT TRACK SPEED THROUGH
TAU 48-60, AT WHICH POINT, THE STORM IS FORECAST TO SLOW SLIGHTLY
AS IT APPROACHES A WEAKNESS BETWEEN THE STEERING RIDGE AND A WEAKER
STR CURRENTLY CENTERED OVER CHINA. BETWEEN TAU 60-72, 25W WILL
CONTINUE TO SLOW ITS SPEED OF ADVANCE AND TURN NORTH-NORTHWESTWARD
INTO THE WEAKNESS AND BEGIN TO TRACK AROUND THE SOUTHWESTERN
PERIPHERY OF THE STEERING RIDGE TOWARDS THE RIDGE AXIS. BY TAU
72-96, 25W IS FORECAST TO RECURVE ABOUT THE STEERING RIDGE WHILE 
TRACKING CONSIDERABLY SLOWER. FROM TAU 96 THROUGH THE END OF THE 
FORECAST PERIOD, 25W WILL BEGIN TO ACCELERATE TO THE NORTH-NORTHEAST 
WHILE THE DEEP-LAYER STR MAINTAINS STEERING AUTHORITY OVER THE SYSTEM.
REGARDING INTENSITY, 25W IS FORECAST TO STEADILY INTENSIFY WHILE IT
CONTINUES TO CONSOLIDATE THROUGH TAU 60. AT THAT POINT, 25W MAY
UNDERGO A PERIOD OF RAPID INTENSIFICATION. THE ENVIRONMENT IS
EXPECTED TO BE HIGHLY FAVORABLE THROUGH THE ENTIRE FORECAST PERIOD,
ESPECIALLY BETWEEN TAU 60-96. DURING THAT TIME, VWS IS EXPECTED TO
DROP INTO THE SINGLE DIGITS AND THE SLOWER TRACK SPEED WILL RESULT
IN 25W SPENDING CONSIDERABLE TIME OVER HIGH OHC VALUES. 25W IS
CURRENTLY FORECAST TO PEAK AT TAU 120, WITH ADDITIONAL
INTENSIFICATION POSSIBLE OUTSIDE THE FORECAST PERIOD. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE DEPICTS A
SIGNIFICANT BIFURCATION SCENARIO BEGINNING AROUND TAU 72 AS 25W
ENTERS THE WEAKNESS BETWEEN THE TWO SUBTROPICAL RIDGES. THE
BIFURCATION IS SPLIT BETWEEN THE PHYSICS-BASED MODELS AND
EXPERIMENTAL AI-BASED MODELS. GLOBAL PHYSICS-BASED MODELS INDICATE
25W COULD FAIL TO RECURVE AND INSTEAD TRANSITION STEERING
INFLUENCES TO THE WEAKER STR OVER CHINA AND TRACK NORTHWESTWARD
INTO TAIWAN. THIS SCENARIO HAS BEEN DEEMED LESS LIKELY, AS THE
WEAKNESS IS DEPICTED IN GLOBAL MODELS AS A SIGNIFICANT GAP BETWEEN
THE TWO RIDGES WHILE THE STR OVER CHINA IS DEPICTED AS IRRESOLUTE.
EXPERIMENTAL AI-BASED MODELS SUPPORT THE RECURVE SCENARIO, AND DUE
TO THE CHARACTERIZATION OF THE ENVIRONMENTAL SETUP IN GLOBAL MODELS
AND THE AI MODELS' HISTORICAL HIGH ACCURACY, THE JTWC TRACK
FORECAST LIES IN CONCURRENCE WITH THE AI MODELS. ADDITIONALLY, THE
EXPECTED INTENSITY OF THE STORM IS FORECAST TO BE SUFFICIENT
TO PUNCH THROUGH THE WEAKNESS AND RECURVE ABOUT THE ORIGINAL
STEERING RIDGE. THE TRACK FORECAST CONFIDENCE IS PLACED WITH MEDIUM
CONFIDENCE FROM TAU 0-72 AND LOW CONFIDENCE FROM TAU 72-120 DUE TO
THE UNCERTAINTY SURROUNDING THE RECURVE SCENARIO. RELIABLE
INTENSITY GUIDANCE IS IN STRONG AGREEMENT IN A STEADY RATE OF
INTENSIFICATION THROUGH TAU 60 AND AN INCREASED RATE OF
INTENSIFICATION THEREAFTER. THE GUIDANCE DIVERGES WITH RESPECT TO
PEAK INTENSITY, RANGING ANYWHERE FROM 85 KTS (GFS) TO 145 KTS
(COAMPS-TC) AT TAU 120. AS A RESULT, THE JTWC INTENSITY FORECAST
LIES VERY CLOSE TO THE HAFS-A SOLUTION AND THE MULTI-MODEL
CONSENSUS, AND IS ASSESSED WITH MEDIUM CONFIDENCE FROM TAU 0-72 AND
LOW CONFIDENCE FROM TAU 72-120.

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