Tropical Storm RAI Advisory 12月16日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (RAI) WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 9.4N 128.9E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 559 NM EAST-SOUTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TY 28W HAS UNDERGONE A PERIOD OF EXTREMELY RAPID INTENSIFICATION
OVER THE PAST SIX HOURS, WITH THE INITIAL INTENSITY INCREASING OVER
30 KNOTS IN THE SIX HOUR PERIOD BETWEEN 1200Z AND 1800Z. ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY OVER THE PREVIOUS FEW
HOURS SHOWS THE RAPID DEVELOPMENT OF A PINHOLE EYE APPROXIMATELY
7NM IN DIAMETER WITH DEEP CONVECTIVE TOWERS ROTATING UPSHEAR TO THE
EAST OF THE EYE. 151626Z AMSR2 89GHZ AND 37GHZ MICROWAVE IMAGES
SHOW THE VERY WELL DEFINED EYE, WHICH IS VERTICALLY STACKED WITH
LITTLE TO NO TILT, INDICATING A VAST IMPROVEMENT FROM THE
PREVIOUSLY TILTED CORE. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE PINHOLE EYE IN BOTH THE EIR AND MICROWAVE
DATA. MODERATE EASTERLY SHEAR, OF AROUND 10-15 KNOTS IS INDICATED
BY THE SHARP UPSHEAR EDGE OF THE CONVECTIVE ENVELOPE AND CIRRUS
SHIELD SEEN IN THE INFRARED AND MICROWAVE IMAGERY. HOWEVER THE
CONVECTIVE TOWERS HAVING MOVED UPSHEAR HAVE SHELTERED THE CORE FROM
THE EASTERLY SHEAR AND ENABLED THE RAPID INTENSIFICATION. THE
INITIAL INTENSITY HAS BEEN INCREASED DRAMATICALLY, TO A
CONSERVATIVE 115 KNOTS, CONSERVATIVE DUE TO THE EXTREMELY RAPID
RATE OF INTENSIFICATION. AGENCY FIXES ARE BEING HELD BY
CONSTRAINTS, BUT DATA-T NUMBERS ARE CLIMBING RAPIDLY, NOW EXCEEDING
T7.0 IN SOME CASES. DUE TO THE SMALL EYE AND RAPIDLY DEVELOPING
SITUATION, THE ADT IS SIGNIFICANTLY BEHIND, THOUGH SUBSEQUENT TO
THE 2000Z HOUR IS BEGINNING TO PICK UP THE EYE, WITH RAW-T NUMBERS
NOW ABOVE T7.0. THE ENVIRONMENT IS VERY FAVORABLE FOR CONTINUED
DEVELOPMENT, WITH WARM (29-30C) SSTS AND ROBUST WESTWARD AND
POLEWARD OUTFLOW. THE SYSTEM WILL ALSO PASS OVER A DEEP POOL OF
WARM WATERS WITH HIGH OHC FROM NOW THROUGH LANDFALL IN THE
PHILIPPINES.
INITIAL WIND RADII BASIS: SCATTEROMETER DATA
CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   KNES: T6.0 - 115 KTS
   CIMSS SATCON: 74 KTS AT 151312Z
   CIMSS ADT: 84 KTS AT 151740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG WESTWARD
   OTHER FACTORS: STRONG POLEWARD OUTFLOW
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THE FORECASTED PEAK INTENSITY HAS
BEEN INCREASED BY 55 KNOTS, FROM 85 KNOTS TO 140 KNOTS.
FORECAST DISCUSSION: AS DISCUSSED EARLIER, TY 28W HAS UNDERGONE A
PERIOD OF EXTREMELY RAPID INTENSIFICATION, WHICH WAS NOT PREVIOUSLY
FORECAST AND WHILE TRACK HAS NOT SIGNIFICANTLY CHANGED, THE
INTENSITY FORECAST HAS BEEN INCREASED DRAMATICALLY. THE SYSTEM IS
TRACKING JUST NORTH OF DUE WEST ALONG THE SOUTHERN SIDE OF A DEEP
STR TO THE NORTH. THE SYSTEM IS FORECAST TO MAKE LANDFALL ALONG THE
NORTHEASTERN TIP OF MINDANAO, NEAR SURIGAO CITY, WITHIN THE NEXT 12
TO 15 HOURS. THE SYSTEM WILL THEN CROSS THE SOUTHERN PORTION OF THE
PHILIPPINE ISLANDS AND INTO THE SULU SEA BY TAU 36. AS THE SYSTEM
MOVES INTO THE SOUTH CHINA SEA, A WEAKNESS IS FORECAST TO DEVELOP
IN THE RIDGE TO THE NORTH, AND THE SYSTEM WILL GRADUALLY TURN
POLEWARD IN RESPONSE, THROUGH THE REMAINDER OF THE FORECAST PERIOD.
THE SYSTEM HAS ANOTHER TWELVE HOURS OVER VERY WARM, HIGH OHC
WATERS, AND NOW THAT THE CORE OF THE SYSTEM HAS VERY OBVIOUSLY
BECOME ESTABLISHED AND IS FIGHTING OFF THE MODERATE EASTERLY SHEAR,
IT IS EXPECTED TO CONTINUE TO RAPIDLY INTENSIFY TO A PEAK OF AT
LEAST 140 KNOTS PRIOR TO LANDFALL. LATE RECEIPT OF A 151930Z SSMIS
89GHZ MICROWAVE IMAGE SUGGESTS THE DEVELOPMENT OF A SECONDARY
EYEWALL ON THE SOUTHERN SIDE OF THE SYSTEM. IF THIS CONTINUES TO
DEVELOP, IT MAY LEAD TO A LOWER INTENSITY AT LANDFALL, BUT THE PEAK
MAY STILL OCCUR PRIOR TO THIS POINT. VWS IS FORECAST TO STRENGTHEN
A BIT AFTER LANDFALL, AND COMBINED WITH THE DISRUPTION OF THE CORE
DUE TO INTERACTION WITH THE COMPLEX TERRAIN OF THE SOUTHERN
PHILIPPINE ISLANDS, WILL LEAD TO A SIGNIFICANT WEAKENING THROUGH
TAU 36. HOWEVER, ONCE THE SYSTEM EMERGES BACK OVER THE SOUTH CHINA
SEA, INCREASED UPPER-LEVEL OUTFLOW AND DECREASED SHEAR WILL ALLOW
FOR A PERIOD OF INTENSIFICATION TO A SECOND PEAK OF 110 KNOTS BY
TAU 72. THEREAFTER A STRONG COLD SURGE WILL BRING COOL, RELATIVELY
DRY-AIR DOWN FROM THE NORTH, AND SOUTHWESTERLY SHEAR WILL INCREASE
SHARPLY AS THE SYSTEM INTERACTS WITH A MID-LATITUDE TROUGH TO THE
WEST. THE COMBINED EFFECTS OF THESE UNFAVORABLE CONDITIONS WILL BE
FAIRLY RAPID WEAKENING AS THE SYSTEM TRACKS NORTHWARD TO THE EAST
OF HAINAN ISLAND.
MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU
72, WITH ONLY MINIMAL SPREAD THROUGH THE FIRST 36 HOURS OF THE
FORECAST AND INCREASES MODESTLY TO 90NM AT TAU 72. SPREAD INCREASES
AFTER TAU 72 AS THE SYSTEM RECURVES POLEWARD, INCREASING TO 175NM
BETWEEN THE JGSM ON THE LEFT AND THE GFS ON THE RIGHT OF THE
ENVELOPE. THE JTWC FORECAST LIES AMONGST THE TIGHT GROUPING THROUGH
TAU 72, THEN JUST SLIGHTER LEFT OF THE MEAN THROUGH TAU 120. DUE TO
TECHNICAL DIFFICULTIES, AVAILABLE INTENSITY GUIDANCE IS VERY
LIMITED, WITH ONLY THE COAMPS-TC BEING AVAILABLE TO SUPPORT THIS
FORECAST. THUS THE INTENSITY FORECAST IS BEING GENERATED USING
ENVIRONMENTAL ANALYSIS AND TRENDS THROUGH THE FIRST 24 HOURS, THEN
GENERALLY FOLLOWS THE COAMPS-TC GUIDANCE THEREAFTER. CONFIDENCE IN
THE INTENSITY FORECAST IS LOW DUE TO THE LACK OF GUIDANCE AND THE
RAPID DEVELOPMENT OF THE SYSTEM IN THE NEAR-TERM.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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