Tropical Storm ATSANI Advisory vie, 14-08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W WARNING NR
01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 17W (SEVENTEEN), LOCATED APPROXIMATELY
326 NM SOUTHWEST OF WAKE ISLAND, HAS TRACKED NORTHWARD AT 05 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS PERSISTENT DEEP CONVECTION WITH FORMATIVE BANDS OVER
THE NORTHERN AND SOUTHERN SEMI-CIRCLE OF A DEVELOPING LOW-LEVEL
CIRCULATION CENTER. A 140336Z SSMI MICROWAVE IMAGE REVEALS BROKEN,
BUT TIGHTLY-CURVED CONVECTIVE BANDING WRAPPING INTO THE CENTER. THE
CURRENT POSITION IS BASED ON THE MSI, AFOREMENTIONED MICROWAVE IMAGE
AND SATELLITE FIXES FROM PGTW AND RJTD WITH GOOD CONFIDENCE. THE
INITIAL INTENSITY OF 25 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF
DVORAK INTENSITY ESTIMATES FROM ALL REPORTING AGENCIES. UPPER-LEVEL
ANALYSIS INDICATES TD 17W IS LOCATED IN AN AREA OF MODERATE (15 TO
20 KNOT) VERTICAL WIND SHEAR (VWS) BEING OFFSET BY THE GOOD RADIAL
OUTFLOW AS EVIDENT ON THE WATER VAPOR IMAGERY. TD 17W IS TRACKING
UNDER THE INFLUENCE OF A WEAK STEERING ENVIRONMENT BETWEEN A
SUBTROPICAL RIDGE (STR) TO THE NORTH AND A NEAR-EQUATORIAL RIDGE
(NER) TO THE SOUTH.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. SLOW AND/OR POSSIBLY QUASI-STATIONARY MOVEMENT IS EXPECTED
OVER THE NEXT 48 HOURS AS THE SYSTEM REMAINS IN A WEAK STEERING
ENVIRONMENT. BY TAU 48, THE STR IS FORECAST TO BUILD AND ASSUME THE
STEERING PATTERN DRIVING TD 17W NORTHWESTWARD. CONCURRENTLY,
MARGINALLY FAVORABLE CONDITIONS WILL PERSIST IN THE NEAR TERM,
ALLOWING SLOW INTENSIFICATION. AFTER TAU 48, IN ADDITION TO
FAVORABLE ENVIRONMENTAL CONDITIONS, IMPROVED UPPER-LEVEL OUTFLOW AND
DECREASING VWS WILL ALLOW THE SYSTEM TO UNDERGO RAPID
INTENSIFICATION (RI) THROUGH TAU 72.
   C. THE SYSTEM WILL MAINTAIN A NORTHWESTWARD TRAJECTORY. FAVORABLE
CONDITIONS WILL PERSIST LEADING TO FURTHER RI. LIMITED MODEL
GUIDANCE INDICATES A SIGNIFICANT DIFFERENCE IN THE TRACK AND TRACK
SPEEDS IN THE SHORT TERM AND A LARGE SPREAD IN THE EXTENDED TAUS.
FOR THIS REASON, THE JTWC TRACK FORECAST CONFIDENCE LEVEL IS LOW.//
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