Tropical Storm DANAS Advisory Fri Jul 19

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 06W (DANAS) WARNING NR
09//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 06W (DANAS), LOCATED APPROXIMATELY 200 NM
WEST-SOUTHWEST OF KADENA AB, HAS TRACKED NORTHWARD AT 18 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION (LLC) WITH DEEP
CONVECTION CONFINED TO THE EASTERN SEMICIRCLE. RECENT MSI (18/06-
08Z) INDICATES THE LLC MAY BE DECOUPLING AND DRIFTING NORTH-
NORTHWESTWARD, WHICH ADDS SOME UNCERTAINTY TO THE EARLY PHASE OF THE
FORECAST TRACK. A 180723Z SSMIS 91GHZ IMAGE ALSO INDICATES A
PARTIALLY-EXPOSED LLC WITH EXTENSIVE DEEP CONVECTIVE BANDING OVER
THE EAST AND SOUTHEAST QUADRANTS. A 180158Z ASCAT IMAGE CONTINUES TO
SHOW A HIGHLY ASYMMETRICAL WIND FIELD WITH AN EXTENSIVE SWATH OF 30
TO 40 KNOT WINDS OVER THE EASTERN SEMICIRCLE, WHICH EXTEND 180-200NM
EAST. OVERALL, THERE IS GOOD CONFIDENCE IN THE 18/06Z POSITION BASED
ON RADAR IMAGERY, SURFACE OBSERVATIONS AND MSI. THE INITIAL
INTENSITY IS ASSESSED AT 40 KNOTS, HEDGED ABOVE DVORAK INTENSITY
ESTIMATES OF T2.5 (35 KNOTS) BASED ON THE AFOREMENTIONED ASCAT DATA.
UPPER-LEVEL ANALYSIS DEPICTS A GENERALLY FAVORABLE ENVIRONMENT WITH
LOW VERTICAL WIND SHEAR AND FAIR OUTFLOW. TS 06W IS TRACKING
NORTHWARD ALONG THE WESTERN PERIPHERY OF A NORTH-SOUTH ORIENTED
SUBTROPICAL RIDGE.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE. FORECAST WIND RADII ARE BASED
ON THE WIND RADII CONSENSUS (RVCN).
   B. TS 06W IS FORECAST TO TRACK NORTHWARD TO NORTH-NORTHEASTWARD
THROUGH TAU 48 ALONG THE NORTHWEST PERIPHERY OF THE SUBTROPICAL
RIDGE (STR). AFTER TAU 48, THE SYSTEM WILL BEGIN TO ROUND THE STR
AND WILL BEGIN TO INTERACT WITH RELATIVELY WEAK MIDLATITUDE
WESTERLIES OVER THE KOREAN PENINSULA. THERE IS MODERATE UNCERTAINTY
IN THE FORECAST TRACK DUE TO THE ASYMMETRIC NATURE OF THE SYSTEM
WITH POTENTIAL FOR A WESTWARD TRACK SHIFT AND LANDFALL ALONG THE
SOUTHWEST COAST OF KOREA IF THE SYSTEM REMAINS DECOUPLED.
FURTHERMORE, THE EXPANSIVE GALE FORCE WINDS OVER THE EASTERN
SEMICIRCLE ARE EXPECTED TO PERSIST DUE TO AN ENHANCED GRADIENT WITH
A STRONG HIGH TO THE EAST. TS 06W IS FORECAST TO INTENSIFY SLIGHTLY
TO A PEAK OF 45 KNOTS BUT SHOULD WEAKEN STEADILY THROUGH TAU 48.
AFTER LANDFALL, THE SYSTEM WILL WEAKEN RAPIDLY OVER THE MOUNTAINOUS
TERRAIN OF KOREA AND SHOULD DISSIPATE BY TAU 72. OVERALL, THERE IS
MODERATE CONFIDENCE IN THE JTWC FORECAST TRACK WITH A SPREAD OF
200NM AT TAU 48.//
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