Tropical Storm HALONG Advisory Seg, 04-11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (HALONG) WARNING NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 24W (HALONG), LOCATED APPROXIMATELY 381 NM SOUTH
OF MINAMI TORI SHIMA, JAPAN, HAS TRACKED NORTHWESTWARD AT 08 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS A CENTRAL DENSE OVERCAST FEATURE, WHICH IS OBSCURING
THE LOW-LEVEL CIRCULATION CENTER (LLCC). HOWEVER, A 040622Z SSMIS
91GHZ IMAGE INDICATES A WELL-DEFINED MICROWAVE EYE FEATURE, WHICH
SUPPORTS THE CURRENT POSITION WITH GOOD CONFIDENCE. THE CURRENT
INTENSITY IS ASSESSED AT 80 KNOTS BASED ON A PGTW DVORAK INTENSITY
ESTIMATE OF T4.5 (77 KNOTS). UPPER-LEVEL ANALYSIS INDICATES A
FAVORABLE ENVIRONMENT WITH RADIAL OUTFLOW, ENHANCED POLEWARD OUTFLOW
AND LOW VERTICAL WIND SHEAR. SST VALUES NEAR 29C ARE ALSO CONDUCIVE
FOR FURTHER DEVELOPMENT. TY 24W IS TRACKING ALONG THE SOUTHWESTERN
PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) POSITIONED TO
THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE. THE 34-KNOT AND 50-KNOT
WIND RADII HAVE BEEN ADJUSTED BASED ON A DETAILED ANALYSIS OF RECENT
ASCAT IMAGERY.
   B. TY 24W WILL TRACK NORTHWESTWARD TO NORTH-NORTHWESTWARD THROUGH
TAU 36 THEN GRADUALLY RECURVE AS IT ROUNDS THE STR AXIS NEAR TAU 48.
AFTER TAU 48, TY 24W WILL ACCELERATE NORTH-NORTHEASTWARD AND IS
FORECAST TO BEGIN EXTRA-TROPICAL TRANSITION (ETT) BY TAU 72 WHEN IT
INTERACTS WITH THE MIDLATITUDE WESTERLIES. NUMERICAL MODEL GUIDANCE
IS IN FAIR AGREEMENT THROUGH TAU 72 WITH SOME UNCERTAINTY IN THE
TIMING OF THE RECURVE. THE SYSTEM WILL INTENSIFY UNDER FAVORABLE
CONDITIONS TO A PEAK OF 115 KNOTS BY TAU 36 DUE TO IMPROVED POLEWARD
OUTFLOW INTO THE MIDLATITUDE WESTERLIES.
   C. IN THE EXTENDED PERIOD, TY 24W WILL ACCELERATE NORTHEASTWARD
AS IT TRACKS WITHIN THE MIDLATITUDE WESTERLIES AND SHOULD COMPLETE
ETT BY TAU 120. HOWEVER, THE SYSTEM IS FORECAST TO SLOW AFTER TAU
120 AS IT ENCOUNTERS A STRONG, LOW-LEVEL MIDLATITUDE HIGH, WHICH MAY
TURN THE SYSTEM MORE POLEWARD. TY 24W WILL WEAKEN RAPIDLY DUE TO
INCREASING VWS AND COOLER SST. WITH THE EXCEPTION OF NVGI AND AFUI,
THE NUMERICAL MODELS ARE IN FAIR AGREEMENT WITH THE TRACK AND TIMING
OF THE RECURVE, THEREFORE, THERE IS MODERATE OVERALL CONFIDENCE IN
THE JTWC TRACK FORECAST.//
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