WDPN32 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (VAMCO)
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM (TS) 25W (VAMCO), LOCATED APPROXIMATELY 444 NM
EAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT
11 KNOTS OVER THE PAST SIX HOURS. MULTISPECTRAL SATELLITE IMAGERY
(MSI) INDICATES THAT TS 25W HAS CONSOLIDATED INTO A WELL DEFINED
SYSTEM, WITH DEEP FLARING CONVECTION ALONG THE SOUTHERN SEMI-CIRCLE
AND SPIRAL BANDING EXTENDING ACROSS THE NORTHERN PORTION OF THE
SYSTEM WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER (LLCC). THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED UPON THE
BANDING FEATURES PRESENT IN A 092217Z SSMIS 37GHZ IMAGE. THE INITIAL
INTENSITY IS ASSESSED AT 35 KTS WITH HIGH CONFIDENCE BASED ON MULTI-
AGENCY DVORAK INTENSITY ESTIMATES OF T2.0 (30 KNOTS) FROM PGTW AND
RJTD, AND AN ADVANCED DVORAK TECHNIQUE (ADT) CURRENT INTENSITY
ESTIMATE OF T2.8 (38 KTS). TS 25W IS TRACKING NORTHWESTWARD ALONG
THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED
TO THE NORTHEAST. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM REMAINS
IN A FAVORABLE POSITION FOR INTENSIFICATION WITH LOW (5-10 KTS)
VERTICAL WIND SHEAR (VWS) AND STRONG DIVERGENCE ALOFT ASSOCIATED
WITH A POINT SOURCE OVER THE VORTEX CENTER. ADDITIONALLY, SEA SURFACE
TEMPERATURES (SST) REMAIN WARM (29-30 CELSIUS) AND OCEAN HEAT CONTENT
(OHC) REMAINS HIGH (120-140 KJ/CM^2).
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
B. IN THE NEAR TERM, TS VAMCO WILL CONTINUE TO TRACK NORTHWESTWARD
THROUGH TAU 12 AND TURN WEST-NORTHWESTWARD BY TAU 24 AS THE STR BUILDS
AND EXTENDS TOWARDS THE WEST ALONG THE 25TH PARALLEL, EFFECTIVELY
BLOCKING THE POLEWARD MOVEMENT. THE SYSTEM WILL CONTINUE TO CONSOLIDATE
AND INTENSIFY TO 90 KTS BY TAU 36 DUE TO A HIGHLY FAVORABLE ENVIRONMENT
WITH CONTINUED LOW (5-10 KTS) VWS, HIGH SST AND OHC, AND IMPROVING
DIVERGENCE ALOFT. DUE TO THE HIGHLY FAVORABLE ENVIRONMENT, THERE IS A
DISTINCT POSSIBILITY OF RAPID INTENSIFICATION DURING THIS TIME. THE
SYSTEM IS THEN FORECAST TO CROSS LAMON BAY AND MAKE LANDFALL ALONG THE
CENTRAL LUZON COAST DUE EAST OF MANILA NEAR TAU 36 BEFORE REEMERGING
INTO THE OPEN WATERS OF THE SOUTH CHINA SEA NEAR TAU 48. WHILE THE
SYSTEM CROSSES LUZON BETWEEN TAU 36 AND TAU 48, INTERACTION WITH THE
RUGGED TERRAIN WILL INDUCE WEAKENING DUE TO FRICTIONAL EFFECTS. AFTER
TAU 48, TS VAMCO WILL ENTER THE SOUTH CHINA SEA (SCS) AND SUBSEQUENTLY
INTENSIFY 75 KTS BY TAU DUE TO A FAVORABLE ENVIRONMENT AT THIS TIME.
DYNAMIC TRACK GUIDANCE IS IN OVERALL GOOD AGREEMENT THROUGH THE TURN
WESTWARD, WITH SOME SLIGHT DIFFERENCES IN THE SHARPNESS OF THE TURN
LEADING TO A SPREAD OF 82 NM AT TAU 48 THROUGH WHICH INCREASES SLIGHTLY
TO 86 NM BY TAU 72. THE TIGHT AGREEMENT IN THE MODEL SOLUTIONS LENDS
OVERALL GOOD CONFIDENCE IN THE INITIAL PORTION OF THE JTWC FORECAST
TRACK WITH IS PLACED NEAR THE JTWC MULTI-MODEL CONSENSUS.
C. AFTER TAU 72, THE SYSTEM WILL TRACK GENERALLY NORTHWESTWARD
THROUGH TAU 120 UNDER THE STEERING INFLUENCE OF THE DEEP-LAYER STR WHICH
WILL RETREAT SLIGHTLY NORTHEAST DURING THIS TIME. AS THE SYSTEM TRACKS
OVER THE SOUTH CHINA SEA IT WILL BEGIN TO WEAKEN AFTER TAU 72 DUE TO
DECREASING SST AND SIGNIFICANTLY LOWER OHC, ULTIMATELY FALLING TO AN
INTENSITY OF 60 KTS BY TAU 120. NUMERICAL MODEL GUIDANCE DEPICTS
INCREASING UNCERTAINTY AFTER TAU 72 WITH CROSS-TRACK SPREAD INCREASING
TO 210 NM BY TAU 120. THIS SLIGHT DIVERGENCE IN MODEL SOLUTIONS DURING
THIS EXTENDED PORTION OF THE JTWC FORECAST TRACK ARISES DUE TO
UNCERTAINTY IN THE EXTENT AND TIMING OF THE REPOSITIONING OF THE
AFOREMENTIONED STEERING RIDGE. SPECIFICALLY, THE DETERMINISTIC NAVGEM
AND AFUM SOLUTIONS, ALONG WITH THE UKMET ENSEMBLE SOLUTION, DEPICT A
RECURVATURE SCENARIO WITH THE VORTEX TRAVELING WEST-NORTHWESTWARD TO
NORTHWESTWARD AND THE REMAINING MODEL MEMBERS PROVIDING A GENERALLY
WESTWARD SOLUTION. THIS INCREASING DIVERGENCE IN MODEL SOLUTIONS LENDS
OVERALL POOR CONFIDENCE IN THIS EXTENDED PORTION OF THE JTWC FORECAST
TRACK WHICH IS LAID SLIGHTLY SOUTH OF THE MULTI-MODEL CONSENSUS.//
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