Tropical Storm ATSANI Advisory Sat Aug 15

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (ATSANI)
WARNING NR 04//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
  TROPICAL STORM (TS) 17W (ATSANI), LOCATED APPROXIMATELY 187 NM
NORTH OF ENEWETAK, HAS TRACKED WESTWARD AT 02 KNOTS OVER THE PAST SIX
HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
PARTIALLY-EXPOSED, WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC)
WITH MULTIPLE CONVECTIVE BANDS WRAPPING INTO THE CENTER. HOWEVER,
MSI INDICATES VERY SLOW TRACK MOTION, PERHAPS QUASI-STATIONARY
MOTION, OVER THE PAST SIX HOURS. OVERALL, THERE IS GOOD CONFIDENCE
IN THE CURRENT POSITION. A 142105Z SSMIS 37 GHZ IMAGE REVEALS
IMPROVED CONVECTIVE STRUCTURE WITH TIGHTLY-CURVED BANDING WRAPPING
INTO THE CENTER. DESPITE THE CONSOLIDATING LLCC, THE DVORAK
ESTIMATES REMAIN AT T2.5 (35 KNOTS), THEREFORE, THE CURRENT
INTENSITY REMAINS ASSESSED AT 35 KNOTS, WHICH IS SUPPORTED BY A
142222Z ASCAT IMAGE SHOWING AN EXPANSIVE AREA OF 30 TO 35 KNOT
WINDS. TS 17W IS EMBEDDED WITHIN A COMPETING STEERING ENVIRONMENT
BETWEEN A SUBTROPICAL RIDGE (STR) TO THE NORTH AND A NEAR-EQUATORIAL
RIDGE (NER) TO THE SOUTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. AS REFLECTED IN THE BULK OF DYNAMIC MODEL GUIDANCE, SLOW,
QUASI-STATIONARY TRACK MOTION IS FORECAST OVER THE NEXT 36 HOURS AS
THE SYSTEM REMAINS IN A COMPETING STEERING ENVIRONMENT. AFTER TAU
36, THE NER IS FORECAST TO WEAKEN AND SHIFT EASTWARD ALLOWING THE
STR TO BUILD AND BECOME THE DOMINANT STEERING INFLUENCE. THIS WILL
ALLOW TS 17W TO ACCELERATE WEST-NORTHWESTWARD TO NORTHWESTWARD
THROUGH TAU 72. TS 17W IS EXPECTED TO RAPIDLY INTENSIFY AFTER TAU 24
UNDER VERY FAVORABLE ENVIRONMENTAL CONDITIONS TO INCLUDE RADIAL
OUTFLOW, WARM SST AND HIGH OCEAN HEAT CONTENT.
   C. IN THE EXTENDED TAUS, TS 17W WILL MAINTAIN A NORTHWESTWARD
TRAJECTORY AS THE SYSTEM TRACKS ALONG THE WESTERN PERIPHERY OF THE
STR. AVAILABLE MODEL GUIDANCE REMAINS IN GOOD AGREEMENT, HOWEVER,
THERE IS LOW OVERALL CONFIDENCE IN THE FORECAST TRACK DUE TO THE
ERRATIC MOTION EXPECTED IN THE SHORT-TERM.//
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