Tropical Storm NAKRI Advisory jue, 07-11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 25W (NAKRI)
WARNING NR 03//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 25W (NAKRI), LOCATED APPROXIMATELY 281 NM WEST-
SOUTHWEST OF MANILA, PHILIPPINES, HAS TRACKED EAST-SOUTHEASTWARD AT
03 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS A SOMEWHAT DISORGANIZED SYSTEM, WITH FLARING
DEEP CONVECTION PRIMARILY CONFINED TO THE WESTERN PERIPHERY OF A
BROAD, BUT CONSOLIDATING, LOW LEVEL CENTER. THE INITIAL POSITION IS
PLACED WITH MODERATE CONFIDENCE BASED ON THE ANIMATED MULTISPECTRAL
IMAGERY, SUPPORTED BY A 060512Z ATMS 81 GHZ MICROWAVE IMAGE, WHICH
SHOWED A WEAK LLC WITH DEEP CONVECTION TO THE WEST AND SOUTH. A WEAK
SPINNER WAS EVIDENT IN ANIMATED MULTISPECTRAL IMAGERY TO THE EAST OF
THE ASSESSED POSITION, BUT THIS WEAK VORTEX WAS EMBEDDED IN THE
GENERAL SOUTHEASTERLY FLOW TO THE EAST OF THE LLC AND IS NOT
REPRESENTATIVE OF THE ACTUAL CENTER OF THE SYSTEM. THE INITIAL
INTENSITY HAS BEEN INCREASED TO 35 KTS BASED ON DVORAK CURRENT
INTENSITY ESTIMATES OF T2.5 (35 KTS) FROM KNES, PGTW, AND RJTD
SUPPORTED BY A SATELLITE CONSENSUS ESTIMATE OF 37 KNOTS. THE SYSTEM
LIES IN A WEAKLY SUPPORTIVE ENVIRONMENT WITH THE SINGLE OUTFLOW
CHANNEL BEING TO THE WEST, LOW (15-20 KNOTS) VWS AND HIGH SSTS
AROUND 29 CELSIUS. WHILE VWS AND SSTS ARE VERY SUPPORTIVE FOR
DEVELOPMENT, THE EASTERLY WINDS OVER TOP OF THE SYSTEM ARE PUSHING
THE DEEP CONVECTION TOWARDS THE WEST, OFF OF THE LLC, CONTRIBUTING
TO THE SLOW OVERALL DEVELOPMENT OVER THE PAST SIX HOURS.  TS 25W IS
MOVING VERY SLOWLY EAST-SOUTHEASTWARD IN A WEAK STEERING
ENVIRONMENT.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 25W IS FORECAST TO DRIFT SLOWLY EAST TO EAST-NORTHEASTWARD
OVER THE NEXT 24 HOUR WITH THE SYSTEM TRAPPED IN A COL REGION
BETWEEN THE NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTH, AND TWO WEAK
SUBTROPICAL RIDGES (STR) TO THE EAST AND WEST. AROUND TAU 36, STRONG
WARM AIR ADVECTION FROM THE REMNANTS OF TS 23W IN THE BAY OF BENGAL
WILL BUILD THE STR OVER NORTHWEST LAOS EXTENDING INTO THE NORTHERN
SOUTH CHINA SEA. AT THIS POINT, THE STR BECOMES THE DOMINATE
STEERING MECHANISM, LEADING TS 25W TO TURN FIRST SOUTHWARD, THEN
WESTWARD BY TAU 36. THEREAFTER THE SYSTEM WILL ACCELERATE WESTWARD
TOWARDS THE COAST OF VIETNAM THROUGH TAU 72. THE SYSTEM IS EXPECTED
TO GRADUALLY INTENSIFY TO A PEAK OF 50 KTS AT TAU 36 DUE TO A
COMBINATION OF HIGH SSTS AND LOW TO MODERATE VWS, OFFSET BY
RELATIVELY STRONG WESTWARD OUTFLOW, LIMITING THE INTENSIFICATION
POTENTIAL. THERE IS VERY HIGH UNCERTAINTY IN THE FIRST 36 HOURS OF
THE FORECAST, WITH TWO DIVERGENT MODEL CLUSTERS. THE HWRF, NAVGEM,
AND GFS SOLUTION MOVES THE SYSTEM SOUTHWARD THROUGH TAU 24 BEFORE
TURNING WESTWARD. THE ALTERNATIVE SOLUTION FAVORED BY THE ECMWF,
ECMWF ENSEMBLE, JGSM, EGRR AND THE GFS ENSEMBLE CONTINUES THE
CURRENT EAST-NORTHEAST MOTION THROUGH TAU 24 BEFORE TURNING WEST.
HOWEVER, ALL MODELS AGREE ON A VERY SLOW, MEANDERING MOTION DURING
THIS TIMEFRAME, AND ALL AGREE ON THE EVENTUAL TURN TO THE WEST AND
TRACK AGREEMENT IS SURPRISINGLY ROBUST BY TAU 72, WITH ONLY 60NM
SPREAD IN ALL MODELS. THE JTWC FORECAST TRACK FAVORS THE NORTHERN
CLUSTER OF MODELS AND IS PLACED NEAR THE MULTIMODEL CONSENSUS, WITH
LOW CONFIDENCE.
C. AFTER TAU 72, ALL MODELS AGREE ON A WESTWARD TRACK TOWARDS
VIETNAM. TS 25W IS FORECAST TO MAKE LANDFALL ALONG THE VIETNAM
COASTLINE SHORTLY AFTER TAU 96. JUST PRIOR TO LANDFALL, A DECREASE
IN SST AND OHC VALUES, COMBINED WITH UPPER LEVEL CONVERGENCE FROM AN
INVERTED TROUGH WILL RESULT IN AN OVERALL WEAKENING OF THE SYSTEM
BEFORE LANDFALL. AFTER LANDFALL, THE SYSTEM WILL RAPIDLY DISSIPATE
OVER THE MOUNTAINOUS TERRAIN OF WESTERN VIETNAM. THERE IS OVERALL
HIGH CONFIDENCE IN THIS PORTION OF THE TRACK, AS ALL MODELS ARE IN
AGREEMENT WITH THE WESTWARD TRACK. THOUGH THE ECMWF SOLUTION HAS
SHIFTED WELL TO THE SOUTH OVER THE PREVIOUS RUN, THE REMAINDER OF
MODEL SOLUTIONS REMAIN IN TIGHT AGREEMENT.//
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