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 AIRMASS 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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