Tropical Storm KALMAEGI Advisory 13 Σεπ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (KALMAEGI) WARNING
NR 09//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 15W (KALMAEGI), LOCATED APPROXIMATELY 492 NM
EAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 07 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
INDICATES A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC) WITH
IMPROVED CORE CONVECTION ASSOCIATED WITH A DEVELOPING CENTRAL DENSE
OVERCAST FEATURE (CDO); ADDITIONALY, CONVECTIVE BANDING HAS IMPROVED
OVER THE WESTERN SEMI-CIRCLE OF THE SYSTEM. THE INITIAL INTENSITY IS
ASSESSED AT 50 KNOTS BASED ON THE IMPROVED STRUCTURE AND DVORAK
INTENSITY ESTIMATES RANGING FROM 45 TO 55 KNOTS. A 121629Z GCOM-W1
COMPOSITE IMAGE DEPICTS MULTIPLE CONVECTIVE BANDS TIGHTLY WRAPPING
INTO A WELL-DEFINED LLCC POSITIONED ON THE NORTHEAST QUADRANT OF THE
CDO, THEREFORE, THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION.
DESPITE MODERATE NORTHEASTERLY VERTICAL WIND SHEAR (VWS), WHICH IS
HINDERING DEEP CONVECTIVE DEVELOPMENT OVER THE NORTHERN SEMI-CIRCLE,
THE OVERALL ENVIRONMENT IS FAVORABLE WITH IMPROVED OUTFLOW INTO A
TUTT CELL LOCATED NEAR GUAM. ADDITIONALLY, THE MODERATE VWS IS BEING
REDUCED BY THE WESTWARD TRACK MOTION AND OUTFLOW HAS A MORE RADIAL
APPEARANCE IN THE ANIMATED WATER VAPOR IMAGERY. RECENT 500 MB
ANALYSES SHOW A STRONG, EAST-WEST ORIENTED SUBTROPICAL RIDGE (STR)
ENTRENCHED TO NORTH AND NORTHWEST.
 3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE, HOWEVER, THE SHORT-TERM INTENSITY
FORECAST HAS BEEN INCREASED SLIGHTLY DUE TO IMPROVED CONSOLIDATION.
   B. TS 15W IS FORECAST TO TRACK WEST-NORTHWESTWARD UNDER THE
STEERING INFLUENCE OF THE STR. IN THE NEXT 24 HOURS, TS 15W IS
EXPECTED TO MAINTAIN MODERATE TRACK SPEEDS (07 TO 09 KNOTS) AS IT
TRANSITS SOUTH OF A BREAK IN THE STR. THEREAFTER, THE SYSTEM SHOULD
ACCELERATE AS IT TRANSITIONS TO THE WESTERN BRANCH OF THE STR, WHICH
IS FORECAST TO STRENGTHEN AS A MIDLATITUDE RIDGE BUILDS OVER EAST
ASIA. TS 15W IS FORECAST TO RAPIDLY INTENSIFY THROUGH TAU 36 UNDER
FAVORABLE ENVIRONMENTAL CONDITIONS TO INCLUDE WARM SST, HIGH OCEAN
HEAT CONTENT AND FAVORABLE OUTFLOW. TS KALMAEGI IS FORECAST TO MAKE
LANDFALL OVER EASTERN LUZON NEAR TAU 42, LEADING TO A TEMPORARY
WEAKENING AS IT CROSSES THE MOUNTAINOUS TERRAIN OF LUZON.
   C. IN THE EXTENDED TAUS, TS 15W IS EXPECTED TO MAINTAIN A WEST-
NORTHWESTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST PERIOD AS
THE STR REMAINS ENTRENCHED TO THE NORTH. FAVORABLE ENVIRONMENTAL
CONDITIONS IN THE SOUTH CHINA SEA (SCS) WILL FURTHER ALLOW TS 15W TO
INTENSIFY AS IT TRACKS ACROSS THE NORTHERN SCS. NEAR TAU 96, TS
KALMAEGI IS FORECAST TO WEAKEN AS IT APPROACHES THE SOUTHERN COAST
OF CHINA. DYNAMIC MODEL GUIDANCE (INCLUDING THE MODEL ENSEMBLES) IS
IN TIGHT AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE IN THE JTWC
FORECAST TRACK, WHICH IS POSITIONED CLOSE TO THE MULTI-MODEL
CONSENSUS.//
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