Tropical Storm NORU Advisory So, 25.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 18W (NORU)
WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 15.0N 123.7E
   INITIAL INTENSITY: 140 KTS
   GEOGRAPHIC REFERENCE: 158 NM EAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
SUPER TYPHOON (STY) 18W HAS UNDERGONE EXTREME RAPID INTENSIFICATION
(ERI) FROM 50 KNOTS AT 240000Z TO THE CURRENT INTENSITY OF 140 KNOTS.
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A ROUND 9NM
EYE, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE, AND A
MORE ASYMMETRIC CENTRAL DENSE OVERCAST. EIR CONTINUES TO INDICATE
TROCHOIDAL MOTION AS THE SYSTEM TRACKS TOWARD DINGALAN BAY. A 242239Z
91GHZ SSMIS MICROWAVE IMAGE REVEALS A COMPACT, 30NM DIAMETER EYEWALL
WITH DEEP CONVECTIVE BANDING PRIMARILY OVER THE WESTERN AND SOUTHERN
SEMICIRCLES. ALTHOUGH STY 18W HAS MAINTAINED EYE TEMPERATURES IN THE
16C TO 21C RANGE OVER THE PAST FEW HOURS, CLOUD TOP TEMPERATURES HAVE
WARMED. HOWEVER, DVORAK INTENSITY ESTIMATES INCREASED TO T7.0 (140
KNOTS) WITH A FAIRLY SIGNIFICANT JUMP IN THE ADT TO 120 KNOTS AND AIDT
TO 124 KNOTS. THE INITIAL INTENSITY IS ASSESSED AT 140 KNOTS BASED ON
THE PGTW AND KNES DVORAK ESTIMATES, HEDGED ABOVE THE ADT AND AIDT
ESTIMATES. ENVIRONMENTAL CONDITIONS ARE HIGHLY FAVORABLE WITH RADIAL
OUTFLOW, LOW VERTICAL WIND SHEAR, WARM SST VALUES AND HIGH OCEAN HEAT
CONTENT.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: THE SYSTEM IS TRACKING ALONG THE
SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) ENTRENCHED TO THE
NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T7.0 - 140 KTS
   RJTD: T6.0 - 115 KTS
   KNES: T7.0 - 140 KTS
   CIMSS ADT: 115 KTS AT 242340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: STY 18W IS FORECAST TO TRACK WESTWARD AND MAKE
LANDFALL IN ABOUT 09 TO 12 HOURS WITH A PEAK INTENSITY OF 140 KNOTS
EXPECTED AT TAU 12. AFTER MAKING LANDFALL, STY 18W WILL WEAKEN RAPIDLY
AS IT CROSSES THE SOUTHERN LUZON, DOWN TO ABOUT 85 KNOTS BY TAU 36.
DUE TO THE SYSTEM'S COMPACT CORE, MORE SIGNIFICANT WEAKENING IS
POSSIBLE, HOWEVER, HEAVY RAINFALL WILL REMAIN A MAJOR PROBLEM ACROSS A
MORE WIDESPREAD AREA. AFTER RE-EMERGING OVER THE SOUTH CHINA SEA, STY
18W IS FORECAST TO RE-INTENSIFY TO A PEAK INTENSITY OF 120 KNOTS JUST
PRIOR TO LANDFALL OVER CENTRAL VIETNAM NEAR TAU 72. ENVIRONMENTAL
CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE ALTHOUGH VERTICAL WIND
SHEAR IS EXPECTED TO GRADUALLY INCREASE TO 15-20 KNOTS BY LANDFALL.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN GOOD AGREEMENT
WITH A 40-45NM SPREAD IN SOLUTIONS AT TAU 12, AND AN 80-120NM SPREAD
IN SOLUTIONS THROUGH THE REMAINDER OF THE FORECAST THUS OVERALL HIGH
CONFIDENCE IN THE JTWC FORECAST TRACK. DUE TO THE POTENTIAL FOR MORE
SIGNIFICANT WEAKENING OVER THE PHILIPPINE ISLANDS AND POTENTIAL FOR
RAPID INTENSIFICATION OVER THE SOUTH CHINA SEA, THERE IS LOW
CONFIDENCE IN THE JTWC INTENSITY FORECAST. RELIABLE INTENSITY GUIDANCE
INDICATES A STEEP DROP IN INTENSITY AS THE SYSTEM TRACKS OVER LAND
WITH A RANGE OF 52 (HWRF) TO 80 (COAMPS-TC) KNOTS WITH RE-
INTENSIFICATION TO 90-122 KNOTS. THE 241800Z COAMPS-TC ENSEMBLE
INDICATES A 30 TO 60 PERCENT PROBABILITY OF RAPID INTENSIFICATION IN
THE TAU 36 TO TAU 60 TIMEFRAME.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: HIGH
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: MEDIUM//
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