Tropical Storm HINNAMNOR Advisory So, 28.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (HINNAMNOR)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 25.8N 149.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 273 NM WEST-NORTHWEST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
SOMETIME NEAR 272100Z, TS 12W BEGAN RAPIDLY CONSOLIDATING NEAR
THE NORTHERN REGION OF AN AREA OF PERSISTENT DEEP CONVECTION. DEEP
CONVECTIVE BANDING FORMED QUICKLY, WRAPPING INTO A WELL-DEFINED
LOW-LEVEL CIRCULATION CENTER (LLCC). THERE WERE ALSO SIGNIFICANT
IMPROVEMENTS IN THE LOW-LEVEL STRUCTURE, ESPECIALLY OVER THE
WESTERN SEMICIRCLE, WITH LOW-LEVEL CLOUD LINES SUPPORTING THE
PRESENCE OF A CLOSED, DEFINED CYCLONE. ADDITIONALLY, POLEWARD
OUTFLOW IMPROVED EXPANDING NORTHWESTWARD AND NORTHWARD AIDED BY A
TUTT CELL AND UPPER-LEVEL TROUGH TO THE WEST AND NORTHWEST. ROBUST
EQUATORWARD OUTFLOW OVER THE EASTERN SEMICIRCLE BOOSTED BY A LARGE
TUTT CELL POSITIONED TO THE SOUTHEAST HAS FURTHER SUPPORTED THE
RAPID DEVELOPMENT OVER THE PAST 12 HOURS. RECENT ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) CONTINUES TO DEPICT TIGHTLY-
CURVED BANDING WRAPPING INTO THE CENTER WITH INTENSE DEEP CONVECTION
FLARING OVER, AND OBSCURING, THE LLCC. A 280742Z SSMIS 91GHZ COLOR
COMPOSITE MICROWAVE IMAGE SHOWS MULTIPLE DEEP CONVECTIVE BANDS OVER
THE NORTHERN SEMICIRCLE WITH CURVED INNER BANDING OVER THE WEST AND
SOUTH QUADRANTS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON MSI AND THE SSMIS IMAGE. THE INITIAL INTENSITY OF 35 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW DVORAK ESTIMATE,
WHICH IS CONSISTENT WITH THE CONVECTIVE STRUCTURE. PGTW AND KNES DATA
T ESTIMATES ARE SLIGHTLY HIGHER AT 3.0 (45 KNOTS) SUGGESTING THE
INTENSITY COULD BE SLIGHTLY HIGHER HENCE MEDIUM OVERALL CONFIDENCE.
ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE WITH LOW VERTICAL WIND SHEAR
(VWS) AND WARM SST (30C) VALUES.
INITIAL WIND RADII BASIS: OTHER
CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTH (EXTENSION OF THE STR) AND NORTHEAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.
FORECAST DISCUSSION: TS 12W IS FORECAST TO TURN GRADUALLY WEST-
NORTHWESTWARD TO WESTWARD OVER THE NEXT 12 TO 36 HOURS AS THE STR
BUILDS TO THE NORTH. A DEEP MIDLATITUDE SHORTWAVE TROUGH CURRENTLY
POSITIONED OVER EASTERN JAPAN IS KICKING NORTHEASTWARD WITH A
MIDLATITUDE RIDGE BUILDING OVER KOREA AND WESTERN JAPAN, WHICH WILL
REINFORCE THE BUILDING STR. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO
REMAIN FAVORABLE THROUGH TAU 24 THUS STEADY INTENSIFICATION IS
ANTICIPATED WITH A PEAK OF 55 KNOTS BY TAU 24. AFTER TAU 24,
INCREASING NORTHEASTERLY VWS (20-25 KNOTS) WILL HINDER DEVELOPMENT
THROUGH TAU 72. AFTER TAU 72, AN APPROACHING MIDLATITUDE TROUGH WILL
WEAKEN THE STR ALLOWING THE SYSTEM TO SLOW, REINTENSIFY WITH IMPROVING
POLEWARD OUTFLOW AND RECURVE POLEWARD TOWARD KYUSHU ISLAND.
MODEL DISCUSSION: DUE TO THE SYSTEM'S RAPID DEVELOPMENT, INTENSITY
GUIDANCE IS LIMITED, SPECIFICALLY NO HWRF AND NO COAMPS-TC YET THUS
THERE IS LOW CONFIDENCE IN THE JTWC INTENSITY FORECAST. THERE IS ALSO
LOW CONFIDENCE IN THE JTWC FORECAST TRACK DUE TO A BIFURCATION IN
MODEL GUIDANCE. ECMWF AND THE ECMWF ENSEMBLE (EPS) INDICATE A SHARP
WEST-SOUTHWESTWARD TO SOUTHWESTWARD TRACK TOWARD TAIWAN DESPITE A
SIMILAR DEPICTION OF THE AFOREMENTIONED MIDLATITUDE SHORTWAVE TROUGH
DIGGING OVER THE EAST CHINA SEA AFTER TAU 72. THE 280000Z ECMWF RUN
REVEALS BINARY INTERACTION IS OCCURRING WITH A WEAKER SYSTEM TO THE
SOUTH, WHICH IS ROTATING THE SYSTEM SOUTHWESTWARD. THIS SCENARIO IS
ASSESSED AS LOW PROBABILITY THUS THE JTWC FORECAST TRACK IS BASED ON
THE SECOND GROUPING OF MODELS WHICH INDICATE A WEST-NORTHWESTWARD TO
NORTHWESTWARD TRACK TOWARD WESTERN JAPAN TOWARD THE BREAK IN THE STR.
THE 280000Z GEFS AND EPS PROBABILISTIC GUIDANCE ALSO INDICATES A
BIFURCATION SCENARIO WITH LARGE MODEL SPREAD. GEFS FAVORS THE RECURVE
SCENARIO WHILE EPS FAVORS THE SOUTHWESTWARD TRACK SCENARIO.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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