Tropical Storm GAEMI Advisory mer, 03.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (GAEMI) WARNING NR
07//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 21W (GAEMI), LOCATED APPROXIMATELY 600 NM EAST OF
HUE, VIETNAM, HAS TRACKED EAST-SOUTHEASTWARD AT 05 KNOTS OVER THE
PAST SIX HOURS. THE CURRENT POSITION IS BASED ON A RECENT SATELLITE
FIX FROM PGTW AND A 022148Z TRMM PASS. THE CURRENT INTENSITY OF 50
KNOTS IS CONSISTENT WITH DVORAK INTENSITY ESTIMATES FROM 45 TO 55
KNOTS AND A RECENT CIMSS SATCON ESTIMATE OF 53 KNOTS. RECENT
ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS DEEP CONVECTION
PERSISTING OVER THE SOUTHERN AND WESTERN PERIPHERIES OF A PARTIALLY-
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) EVIDENT IN THE
AFOREMENTIONED TRMM PASS. TS 21W LIES JUST TO THE SOUTHWEST OF AN
UPPER-LEVEL ANTICYCLONE CENTER, WITH LOW TO MODERATE NORTHEASTERLY
VERTICAL WIND SHEAR AND FAVORABLE WESTWARD OUTFLOW ALOFT. TS 21W IS
TURNING EQUATORWARD AS THE PRIMARY STEERING INFLUENCE TRANSITIONS
FROM A NEAR-EQUATORIAL RIDGE TO THE SOUTH TO A BUILDING SUBTROPICAL
RIDGE TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO MAJOR CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE. THE TAU 12 THROUGH TAU 24
FORECAST POSITION HAVE BEEN ADJUSTED SLIGHTLY WESTWARD FROM THE
PREVIOUS WARNING BECAUSE THE SYSTEM HAS TRACKED A BIT FARTHER TO THE
WEST IN THE PAST SIX HOURS THAN PREVIOUSLY EXPECTED.
   B. TS 21W IS FORECAST TO SLOW DOWN AND BECOME QUASI-STATIONARY
OVER THE NEXT 12 TO 24 HOURS AS THE SYSTEM CONTINUES TRANSITIONING
TO THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGE BUILDING TO THE
NORTH. THE SUBTROPICAL RIDGE IS BUILDING RELATIVELY SLOWLY AS A
DEEP, BROAD TROUGH, WHICH HAS DOMINATED EAST CHINA AND THE EAST
CHINA SEA, MOVES OUT. AFTER TAU 24, THE SUBTROPICAL RIDGE WILL BUILD
MORE RAPIDLY EASTWARD AND PROVIDE A STRONGER WESTWARD STEERING
INFLUENCE, RESULTING IN A SHARP WESTWARD TURN AND A MARKED
ACCELERATION. DESPITE THE COMPLEX SCENARIO, DYNAMIC MODEL GUIDANCE
HAS BEEN CONSISTENT OVER THE PAST 2 DAYS AND IS IN GOOD AGREEMENT.
THERE IS SOME UNCERTAINTY, HOWEVER, IN THE TIMING OF THIS WESTWARD
TURN AND THE EXACT TRACK MOTION THROUGH TAU 36, THEREFORE, THERE IS
LOW CONFIDENCE IN THE FORECAST TRACK THROUGH TAU 36. AFTER TAU 36,
THERE IS INCREASING CONFIDENCE DUE TO THE TIGHT GROUPING OF DYNAMIC
MODELS, WHICH TRACK THE SYSTEM WESTWARD. TS 21W IS FORECAST TO
INTENSIFY THROUGH TAU 72 UNDER GENERALLY FAVORABLE CONDITIONS.
    C. IN THE EXTENDED TAUS, TS 21W IS FORECAST TO ACCELERATE
WESTWARD AND MAKE LANDFALL ALONG THE EAST COAST OF VIETNAM AFTER TAU
72. THE SYSTEM WILL DISSIPATE BY TAU 120 AS IT INTERACTS WITH THE
RUGGED TERRAIN OF THIS REGION. DYNAMIC MODEL GUIDANCE IS IN GOOD
AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE IN THIS PORTION OF
THE TRACK FORECAST.//
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