Tropical Storm SANVU Advisory Tue May 22

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 03W (SANVU) WARNING NR
04//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 03W, LOCATED APPROXIMATELY 45 NM WEST OF
ANDERSEN AFB, GUAM, HAS TRACKED NORTH-NORTHWESTWARD AT 08 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTI-SPECTRAL  SATELLITE IMAGERY (MSI)
REVEALS THAT TS 03W HAS CONTINUED TO CONSOLIDATE OVER THE PAST SIX
HOURS AND IS NOW A TIGHTLY WRAPPED, SYMMETRIC SYSTEM. THE DEEPEST
CONVECTION IS WITHIN A BAND ALONG THE SOUTHERN SEMI-CIRCLE, WHILE
CONVECTION IS CURRENTLY SUPPRESSED OVER THE NORTHERN SEMI-CIRCLE.
THIS ASSESSMENT IS SUPPORTED BY A 212244Z SSMIS MICROWAVE IMAGE.
ADDITIONALLY, THE SYSTEM HAS A CLEAR BANDING EYE FEATURE ON RADAR.
THE CURRENT POSITION IS BASED ON RADAR FIXES FROM PGUA WITH GOOD
CONFIDENCE. THE MOST RECENT DVORAK ESTIMATES RANGE FROM 30 TO 35
KNOTS FROM PGTW, KNES AND RJTD; HOWEVER, THE LACK OF CONVECTION ON
THE NORTHERN PERIPHERY IS PERHAPS RESULTING IN A SLIGHT UNDER-
ESTIMATE. RADAR AND SURFACE OBSERVATIONS ON GUAM SUPPORT AN INITIAL
INTENSITY OF 40 KNOTS. THEREFORE, THE INITIAL INTENSITY IS ASSESSED
AT 40 KNOTS. UPPER LEVEL ANALYSIS INDICATES A TROPICAL UPPER
TROPOSPHERIC TROUGH (TUTT) TO THE NORTH OF TS 03W, WHICH IS
RESPONSIBLE FOR SUBSIDENCE TO THE NORTH AND LIKELY CAUSING THE
SUPPRESSION OF CONVECTION.  TS 03W IS TRACKING ALONG THE
SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) CENTERED TO
THE NORTHEAST. UPPER LEVEL ANALYSIS AND ANIMATED WATER VAPOR IMAGERY
INDICATE A FAVORABLE ENVIRONMENT FOR CONTINUED DEVELOPMENT.  RADIAL
OUTFLOW REMAINS GOOD, WITH A POSSIBLE NEW TUTT CELL FORMING TO THE
NORTHEAST. ADDITIONALLY, THE WATER VAPOR LOOP SHOWS THAT THE SYSTEM
MAY BE INTERACTING WITH A TROUGH TO THE NORTHWEST, FURTHER ENHANCING
OUTFLOW. THE CURRENT VERTICAL WIND SHEAR (VWS) IS LIGHT, AT 10
KNOTS, AND THE SEA SURFACE TEMPERATURE IS FAVORABLE AT 29-30 DEGREES
CELSIUS.
3. FORECAST REASONING.
   A. THE FORECAST PHILOSOPHY HAS NOT CHANGED SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. AN EXTENSION OF THE STR TO THE NORTH OF THE SYSTEM IS EXPECTED
TO WEAKEN AS AN APPROACHING MID-LATITUDE TROUGH, EXTENDING FROM A
LOW CURRENTLY DEVELOPING SOUTH OF JAPAN, INTERACTS WITH THE RIDGING.
TS 03W SHOULD CONTINUE TO PASS WEST OF GUAM AND SAIPAN, TRACKING
GENERALLY NORTHWESTWARDS AROUND THE ERODING STR PERIPHERY. AFTER TAU
48 THE SYSTEM SHOULD BEGIN TO ROUND THE STR TOWARDS A RE-CURVATURE
INTO THE MID- LATITUDES. THE INTENSITY SHOULD CONTINUE TO INCREASE
THROUGH TAU 48 AS THE UPPER-LEVEL ENVIRONMENT REMAINS FAVORABLE. THE
FORECAST CALLS FOR A PEAK INTENSITY OF 80 KNOTS AT TAU 48. AFTER TAU
48, THE INTENSITY WILL BEGIN TO DECREASE DUE TO AN INCREASE IN VWS
AND DECREASE IN OCEAN HEAT CONTENT, WHICH DROPS OFF POLEWARD OF 24
DEGREES NORTH.
   C. AFTER TAU 72, TS 03W IS FORECAST TO MOVE NORTH OF THE STR AXIS
AND BEGIN TO INTERACT WITH THE MID-LATITUDE BAROCLINIC ZONE, WHICH
IS EXPECTED TO BE VERY ZONAL AND POLEWARD OF ABOUT 30 DEGREES NORTH.
EXTRA-TROPICAL TRANSITION (ETT) SHOULD BEGIN AFTER TAU 72 WITH
COMPLETION INTO THE WESTERLIES AFTER TAU 96. MOST MODELS ARE IN
AGREEMENT WITH THIS SCENARIO, SHOWING THE SYSTEM FULLY INCORPORATED
IN THE MID- LATITUDE WESTERLIES BY TAU 120. THE GFS AND COAMPS
MODELS ARE THE RIGHT-MOST TRACK OUTLIERS, AND THEREFORE FASTEST TO
RE-CURVE, WHILE THE NOGAPS AND WBAR ARE ON THE LEFT OF THE ENVELOPE,
WITH GFDN IN-BETWEEN. THE UKMET AND JGSM MODELS ARE FURTHER WEST,
TAKING 03W INTO A WEAKNESS IN THE RIDGE EXTENSION, WITH A WEAKER MID-
LATITUDE TROUGH THAT DOES NOT INITIATE RECURVATURE. THE OFFICIAL
JTWC TRACK FORECAST STAYS JUST TO THE RIGHT OF  CONW DURING THE
FIRST 36 HOURS, THEN SLIGHTLY FASTER THAN THE CONW AFTER THAT TIME,
TAKING INTO ACCOUNT UKMET AND JGSM, WHICH ARE SLOWING THE CONSENSUS
DOWN.//
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