Tropical Storm NAMTHEUN Advisory 01 Σεπ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN)
WARNING NR 03//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 15W (NAMTHEUN), LOCATED APPROXIMATELY 162 NM
SOUTH OF KADENA AB, HAS TRACKED NORTHEASTWARD AT 13 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND A
312220Z 91 GHZ SSMIS IMAGE SHOWS A BAND OF DEEP CONVECTION WRAPPING
INTO AN AREA OF FLARING CENTRAL CONVECTION FORMING A DISTINCT COMMA
SHAPE, AND GIVING HIGH CONFIDENCE TO THE INITIAL POSITION. THE
INITIAL INTENSITY IS ASSESSED AT 30 KNOTS AND IS BASED ON THE
IMPROVING CONVECTIVE STRUCTURE AND DVORAK ESTIMATES FROM PGTW AND
RJTD REPORTING T2.0 (30 KNOTS). UPPER-LEVEL ANALYSIS INDICATES AN
IMPROVING ENVIRONMENT WITH A NEWLY FORMED POLEWARD OUTFLOW CHANNEL
AND LOW VERTICAL WIND SHEAR. SOUTHWESTERLY FLOW IS CREATING SOME
SUBSIDENCE ON THE WESTERN PERIPHERY AND HINDERING THE EQUATORWARD
OUTFLOW. SEA SURFACE TEMPERATURES ARE VERY FAVORABLE, NEAR 30
CELSIUS. CURRENTLY TD 15W IS TRACKING NORTHEAST ALONG THE PERIPHERY
OF A MID TO LOW LEVEL NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. IN THE NEAR-TERM TD 15W WILL CONTINUE TO TRACK NORTHWEST UNDER
THE INFLUENCE OF THE STEERING RIDGE FOR THE FIRST 24 HOURS. FROM TAU
24 TO 48 TD 15W WILL ENTER A WEAK STEERING ENVIRONMENT AS THE NER
MOVES OFF TO THE SOUTHWEST AND A SUBTROPICAL RIDGE BUILDS IN FROM
THE NORTHEAST. INTENSIFICATION IS EXPECTED OVER THE NEXT 24 TO 36
HOURS AS UPPER-LEVEL CONDITIONS IMPROVE OVER FAVORABLE
WATERS REACHING A PEAK INTENSITY OF 50 KNOTS. THIS PERIOD OF
INTENSIFICATION WILL END ABRUPTLY WHEN THE SUBTROPICAL RIDGE BUILDS
SUFFICIENTLY TO STEER TD 15W NORTH-NORTHWESTWARD INTO A DEEPENING
TROUGH POSITIONED OVER THE EAST CHINA SEA. HIGH VERTICAL WIND SHEAR
WILL WEAKEN TD 15W TO A WEAK TROPICAL STORM BY TAU 72.
   C. IN THE EXTENDED FORECAST BEYOND TAU 72, TD 15W WILL FURTHER
WEAKEN UNDER THE INFLUENCE OF THE UPPER-LEVEL TROUGH BELOW TROPICAL
STORM STRENGTH. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH
TAU 24 AND WITH OVERALL FORECAST PHILOSOPHY. HOWEVER, DUE TO THE
WEAK STEERING ENVIRONMENT AFTER TAU 24, THE TRACKS DIVERGE SOMEWHAT
DUE TO UNCERTAINTY IN THE SUBTROPICAL RIDGE BUILDING SUFFICIENTLY TO
DOMINATE STEERING. DUE TO THE UNCERTAINTY IN THE STEERING
ENVIRONMENT THERE IS LOW CONFIDENCE IN THE FORECAST
TRACK.//
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