Tropical Storm KALMAEGI Advisory Sat Sep 13

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (KALMAEGI) WARNING
NR 10//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 15W (KALMAEGI), LOCATED APPROXIMATELY 454 NM
EAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD 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 CENTRAL DENSE
OVERCAST FEATURE (CDO); ADDITIONALLY, CONVECTIVE BANDING HAS
IMPROVED OVER THE WESTERN SEMI-CIRCLE OF THE SYSTEM. THE INITIAL
INTENSITY IS ASSESSED AT 55 KNOTS BASED ON THE IMPROVED STRUCTURE
AND DVORAK INTENSITY ESTIMATES OF 55 KNOTS. A 122356Z GMI IMAGE AND
A 122252Z SSMIS IMAGE DEPICT MULTIPLE CONVECTIVE BANDS TIGHTLY
WRAPPING INTO A WELL-DEFINED LLCC POSITIONED ON THE NORTH 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.
   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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