Advisories

WDPN31 PGTW 071500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 22W (KROVANH) 
WARNING NR 026//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.2N 132.9E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 337 NM SOUTH-SOUTHEAST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL 
DEPRESSION 22W (KROVANH) WITH A PARTIALLY EXPOSED LOW-LEVEL 
CIRCULATION CENTER (LLCC) AND FLARING CONVECTION DISPLACED TO THE 
NORTHWEST OF THE CENTER. THE CONVECTION IS CLEARLY BEING SHEARED TO 
THE NORTHWEST, WHICH IS CAUSED BY MODERATE TO HIGH SOUTHEASTERLY SHEAR 
ACTING ON THE SYSTEM. A DRY AND STABLE AIR MASS TO THE NORTHWEST CAN 
BE SEEN WRAPPING INTO THE VORTEX, INDICATED BY THE FIELD OF 
STRATOCUMULUS CLOUDS IN THE VICINITY OF KYUSHU. A 071157Z ASCAT 
SCATTEROMETER PASS REVEALED A DEFINED CENTER WITH 30 KNOT WINDS 
CONFINED TO THE EASTERN SEMICIRCLE. THE INITIAL POSITION AND INTENSITY 
ARE BOTH PLACED WITH HIGH CONFIDENCE BASED ON THE TIMELY ASCAT WIND 
VECTOR DATA. THE AGENCY DVORAK FIXES OF T1.5-2.0 FURTHER SUPPORT THE 
INITIAL INTENSITY ESTIMATE. ENVIRONMENTAL ANALYSIS INDICATES THAT 22W 
REMAINS WITHIN A MARGINAL ENVIRONMENT, CHARACTERIZED BY MODERATE 
POLEWARD OUTFLOW ALOFT, 20-25 KTS SOUTHEASTERLY VERTICAL WIND SHEAR, 
EXTENSIVE DRY AIR ENTRAINMENT, AND WARM (28-29 C) SEA SURFACE 
TEMPERATURES.

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

CURRENT STEERING MECHANISM: THE WESTERN FLANK OF A SUBTROPICAL RIDGE 
(STR) CENTERED SOUTHEAST OF JAPAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RCTP: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
   CIMSS ADT: 45 KTS AT 071140Z
   CIMSS AIDT: 39 KTS AT 071140Z
   CIMSS D-PRINT: 30 KTS AT 071140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT FROM THE WEST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 22W IS FORECAST TO TRACK NEARLY DUE NORTH, 
ALONG THE WESTERN PERIPHERY OF THE STR TO THE EAST THROUGH TAU 24.
FOLLOWING TAU 24, THE SYSTEM IS EXPECTED TO TURN NORTHEASTWARD AS IT 
ROUNDS THE STEERING RIDGE AXIS. 22W IS FORECAST TO THEN SKIRT THE 
SOUTHERN COAST OF JAPAN, NEAR THE SHIKOKU AND KANSAI REGIONS AROUND 
TAU 36. JUST AFTER TAU 36, THE SYSTEM WILL INTERACT WITH A DEVELOPING 
FRONTAL BOUNDARY DRAPED ACROSS HONSHU. THIS WILL LIKELY CAUSE 22W TO 
STRETCH AND MOVE UNPREDICTABLY AS THE VORTEX WASHES OUT OVER JAPAN. IN 
TERMS OF INTENSITY, 22W IS FORECAST TO MAINTAIN ITS CURRENT INTENSITY 
OF 30 KTS THROUGH TAU 24 UNDER THE EFFECTS OF THE MARGINAL 
ENVIRONMENT. DRY AIR ENTRAINMENT AND SOUTHERLY SHEAR IS EXPECTED TO 
WORSEN THROUGH THIS TIME, HOWEVER, THE POLEWARD OUTFLOW CHANNEL WILL 
IMPROVE. AFTER TAU 24, SOUTHWESTERLY SHEAR WILL SIGNIFICANTLY 
INCREASE, CAUSING 22W TO WEAKEN JUST BEFORE MAKING LANDFALL IN JAPAN. 
THE SHALLOW VORTEX WILL THEN RAPIDLY ERODE AND STRETCH OVER THE 
MOUNTAINOUS TERRAIN WITH DISSIPATION FORECAST TO OCCUR BY TAU 48.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN WORSE AGREEMENT COMPARED 
TO THE PREVIOUS MODEL RUN. THE PHYSICS-BASED DETERMINISTIC MODELS NOW 
SHOW THE VORTEX STALLING SOUTH OF SHIKOKU NEAR TAU 36, LIKELY DUE TO 
THE RIDGE OVER EASTERN CHINA BUILDING AND EXTENDING EASTWARD AROUND 
THAT TIME. ON THE OTHER HAND, THE AI-BASED MODELS CONTINUE TO SHOW A 
CLEAN RECURVE TO THE NORTHEAST. THE LATTER SCENARIO IS ANALYZED TO BE 
MORE LIKELY, PRIMARILY DUE TO THE SIGNIFICANT DIFFERENCE IN STRENGTH 
BETWEEN THE TWO RIDGES. THE RIDGE TO THE EAST IS MUCH STRONGER AND THE 
STEERING GRADIENT IS MORE PRONOUNCED, CAUSING THE RECURVE SCENARIO TO 
BE THE MORE LIKELY OUTCOME. AS A RESULT, THE JTWC TRACK FORECAST IS 
PLACED NEAR THE CONSENSUS THROUGH TAU 24 AND THEN FAVORS THE AI-BASED 
MODEL DEPICTION THROUGH TAU 48. THERE IS A LARGE AMOUNT OF UNCERTAINTY 
IN THE TRACK AFTER TAU 36, DUE TO THE INTERACTION WITH THE FRONTAL
BOUNDARY AND ENSEMBLE MODELS SHOW AN EXTREME ALONG-TRACK SPREAD AT
THAT TIME. INTENSITY GUIDANCE IS NOW ALSO SPLIT WITH THE HAFS-A AND
THE GFS BOTH BEING MODELS THAT STALL THE VORTEX OVER WATER. IF THIS 
SCENARIO DOES OCCUR, THEN THERE IS A CHANCE FOR MARGINAL 
INTENSIFICATION. AS IT STANDS, THE EXPERIMENTAL GOOGLE DEEPMIND 
ENSEMBLE MEAN, WHICH BETTER ALIGNS WITH THE JTWC TRACK FORECAST, SHOWS 
WEAKENING AFTER TAU 24. THE JTWC INTENSITY FORECAST IS SET NEAR THE 
GOOGLE DEEPMIND WITH MEDIUM CONFIDENCE.

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