Tropical Storm FOUR Advisory Sun Jun 30

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (FOUR)
WARNING NR 03//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 04W (FOUR), LOCATED APPROXIMATELY 417 NM
NORTH-NORTHWEST OF KAYANGEL, PALAU HAS TRACKED NORTHWESTWARD AT 06
KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON
LOW-LEVEL BANDING EVIDENT IN RECENT ANIMATED MULTI-SPECTRAL SATELLITE
IMAGERY AND A 290445Z AMSR 89GHZ MICROWAVE IMAGE. THE INTENSITY OF 35
KNOTS IS HEDGED SLIGHTLY ABOVE RECENT SUBJECTIVE DVORAK ESTIMATES OF
T2.0 FROM PGTW AND KNES, IN LINE WITH 290045Z SATCON AND A 290610Z
ADT ESTIMATE OF 35 KNOTS. TS 04W HAS TRACKED NORTHWESTWARD ALONG THE
PERIPHERY OF A SUBTROPICAL STEERING RIDGE SITUATED TO THE NORTH AND
EAST OVER THE PAST SIX HOURS. DEEP CONVECTION CONTINUES TO FLARE OVER
THE SOUTHWESTERN PORTION OF THE LOW LEVEL CIRCULATION CENTER (LLCC)
AS THE SYSTEM EXPERIENCES PERSISTENT NORTHEASTERLY VERTICAL WIND
SHEAR (VWS). THE SEA SURFACE TEMPERATURE IN VICINITY OF THE LLCC IS
VERY SUPPORTIVE AT 29 TO 30 DEGREES CELSIUS.
3. FORECAST REASONING.
   A. EXTENDED RANGE FORECAST INTENSITIES HAVE BEEN SLIGHTLY
INCREASED FROM THE PREVIOUS WARNING. HOWEVER, THERE IS NO MAJOR
CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS WARNING.
  B. TS 04W IS EXPECTED TO TRACK NORTHWESTWARD IN THE NEAR TERM UNDER
THE CONTINUED STEERING INFLUENCE OF THE SUBTROPICAL RIDGING TO THE
NORTH AND EAST. VWS WILL STAY MODERATE THROUGH TAU 36, UNTIL
GRADUALLY INCREASING AS THE SYSTEM APPROACHES TAIWAN, LIMITING
INTENSIFICATION TO A SLOW RATE DESPITE PASSAGE OVER VERY WARM WATER
AND FAVORABLE SOUTHWESTWARD DIFFLUENCE ALOFT. NUMERICAL MODEL TRACK
FORECAST GUIDANCE REMAINS SPLIT, WITH A GROUPING CONSISTING OF THE
GEFS ENSEMBLE AND HWRF MODELS PREDICTING A TRACK TO THE SOUTH OF
TAIWAN AND THE ECMWF, UKMET, NAVGEM AND AFUM MODELS PREDICTING A
TRACK FARTHER TO THE NORTH. THE CURRENT FORECAST IS CONSERVATIVELY
CONSISTENT WITH THE PREVIOUS JTWC TRACK FORECAST AND CURRENT
MULTI-MODEL CONSENSUS THROUGH TAU 72. THE EXACT TRACK WILL DEPEND ON
THE ORIENTATION OF THE AFOREMENTIONED SUBTROPICAL STEERING RIDGE
DURING THIS PERIOD.
   C. TS 04W IS EXPECTED TO BEGIN WEAKENING IN THE EXTENDED RANGE IN
RESPONSE TO INCREASING VWS AND LAND INTERACTION. NUMERICAL MODEL
TRACK FORECAST SPREAD IS PARTICULARLY PRONOUNCED IN THE EXTENDED
RANGE. A FEW CONSENSUS MODELS DEPICT TS 04W TURNING WESTWARD AND
INTERACTING WITH A DEVELOPING CIRCULATION IN THE NORTHERN SOUTH
CHINA SEA, WHILE OTHER MODELS DEPICT TS 04W MAINTAINING A
NORTHWESTWARD TRACK OR TURNING POLEWARD ALONG THE STEERING RIDGE
PERIPHERY. THE CURRENT TRACK FORECAST IS SET NORTHWESTWARD BASED ON
EXPECTATIONS OF SLOW BUT SUFFICIENT NEAR TERM INTENSIFICATION.
OVERALL, THERE IS LOW CONFIDENCE IN THE CURRENT JTWC TRACK
FORECAST.//
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