Tropical Storm HALONG Advisory 02 Αυγ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (HALONG) WARNING NR 18//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 11W (HALONG), LOCATED APPROXIMATELY 332 NM NORTH-
NORTHWEST OF YAP, HAS TRACKED WESTWARD AT 10 KNOTS OVER THE PAST
SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
DEPICTS A 30 NM DIAMETER EYE WITH TIGHTLY-CURVED CONVECTIVE BANDING
WRAPPING INTO A DEVELOPING LOW-LEVEL CIRCULATION CENTER. A 011720Z
NOAA-19 MICROWAVE IMAGE ALSO REVEALS IMPROVED DEEP CONVECTION AROUND
A WELL-DEFINED MICROWAVE EYE. THE CURRENT POSITION IS BASED ON THE
EYE FEATURE IN THE EIR ANIMATION WITH HIGH CONFIDENCE. THE INITIAL
POSITION HAS INCREASED TO 75 KNOTS BASED ON INCREASED CONSOLIDATION
AND CONSISTENT DVORAK INTENSITY ESTIMATES FROM PGTW AND KNES. UPPER-
LEVEL ANALYSIS INDICATES A WEST TO EAST ORIENTED UPPER-LEVEL TROUGH
DIRECTLY OVER THE NORTHERN EDGE OF TY HALONG, ENHANCING EASTWARD
OUTFLOW AS EVIDENT IN THE WATER VAPOR IMAGERY. ADDITIONALLY, THE
SYSTEM IS LOCATED IN AN AREA OF MODERATE (15 TO 25) NORTHERLY
VERTICAL WIND SHEAR (VWS) OFFSET BY VIGOROUS EQUATORWARD OUTFLOW. TY
11W IS CURRENTLY TRACKING WESTWARD ALONG THE SOUTHERN PERIPHERY OF
THE SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. JTWC FORECAST INTENSITY HAS INCREASED FROM PREVIOUS WARNING
DUE TO INCREASED CONSOLIDATION WITH A 30-NM DIAMETER EYE AND AN
OVERALL INCREASE IN DYNAMICAL-STATISTICAL INTENSITY GUIDANCE;
THEREFORE, THE PEAK INTENSITY HAS BEEN INCREASED TO 105 KNOTS AT TAU
72.
   B. TY 11W IS EXPECTED TO MAINTAIN ITS WEST TO WEST-NORTHWEST
TRACK UNDER THE STEERING INFLUENCE OF THE STR TO THE NORTH OVER THE
NEXT 24 TO 36 HOURS. BETWEEN TAU 36 AND 48, A MIGRATORY UPPER-LEVEL
TROUGH LOCATED TO THE NORTHEAST OF NORTHERN JAPAN IS FORECAST TO
EXTEND SOUTHWESTWARD, MODIFYING THE STR AND CAUSING TY HALONG TO
TURN NORTHWESTWARD. IN ADDITION TO WARM SEA SURFACE TEMPERATURES
(SST), UPPER-LEVEL CONDITIONS ARE EXPECTED TO IMPROVE WITH FAVORABLE
OUTFLOW AND DECREASED VWS, ALLOWING FURTHER INTENSIFICATION THROUGH
TAU 72.
   C. AFTER TAU 72, THE STR IS EXPECTED TO REORIENT TO THE EAST OF
TY 11 AND WILL ASSUME THE STEERING PATTERN, PERMITTING TY HALONG TO
TRACK NORTH-NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF THE STR
THROUGH THE REMAINDER OF THE FORECAST PERIOD. FAVORABLE ENVIRONMENT
IS EXPECTED TO PERSIST, LEADING TO A PEAK INTENSITY OF 105 KNOTS
THROUGH TAU 96. AFTER TAU 96, TY 11W IS EXPECTED TO SLOWLY WEAKEN
DUE TO INCREASING VWS AS IT GAINS LATITUDES. NUMERIC MODEL GUIDANCE
IS IN GOOD AGREEMENT THROUGH TAU 72 AND SLIGHTLY DIVERGES IN THE
LATER TAUS DUE TO STEERING ENVIRONMENT. GFS AND ECMWF ARE IN
AGREEMENT SHOWING THAT THE STR WILL LEAD TY 11W EASTWARD OF KADENA,
WHILE NAVGEM INDICATES A MORE WESTWARD TRACK. DUE TO THE UNCERTAINTY
IN THE NEAR TERM TRACK AND INTENSITY FORECAST ALONG WITH DIVERGENCE
IN THE MODEL GUIDANCE AT EXTENDED TAUS, THERE IS OVERALL LOW
CONFIDENCE IN THE JTWC FORECAST, WHICH IS POSITIONED CLOSE TO MULTI-
MODEL CONSENSUS.//
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