Tropical Storm DANAS Advisory Thu Jul 18

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 06W (DANAS) WARNING NR
05//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM (TS) 06W (DANAS), LOCATED APPROXIMATELY 504 NM SOUTH-
SOUTHWEST OF KADENA AB, HAS TRACKED NORTH-NORTHEASTWARD AT 09 KNOTS
(KTS) OVER THE PAST SIX HOURS. THERE IS HIGH CONFIDENCE IN THE
INITIAL POSITION BASED ON A FULLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) EVIDENT IN ANIMATED MULTISPECTRAL SATELLITE IMAGERY.
THERE IS LITTLE TO NO CONVECTION NEAR THE LLCC BUT THERE ARE TWO
AREAS OF DEEP CONVECTION (90W TO THE EAST, 91W WEST OF THE
PHILIPPINES) ALONG THE PERIPHERY OF THE CIRCULATION. PREVIOUS ASCAT
PASSES AND MICROWAVE IMAGERY REVEAL THAT NEITHER INVEST HAS A
DEFINED LLCC ALTHOUGH BOTH BEAR MONITORING. THE INITIAL INTENSITY OF
35 KTS IS HEDGED SLIGHTLY ABOVE MULTI-AGENCY DVORAK CURRENT
INTENSITY ESTIMATES FROM T1.5-T2.0 (25-30 KTS) BASED ON THE STRONG
WINDS MEASURED BY PREVIOUS ASCAT PASSES AND THE FACT THAT THE DVORAK
TECHNIQUE IS NOT WELL-SUITED TO ESTIMATE INTENSITY FOR MONSOON
DEPRESSIONS. THE ENVIRONMENT IS MARGINAL OVERALL WITH GOOD
EQUATORWARD OUTFLOW, IMPROVING POLEWARD OUTFLOW, AND WARM (30-31
CELSIUS) SEA SURFACE TEMPERATURE BEING PARTIALLY OFFSET BY MODERATE
(15-25 KTS) VERTICAL WIND SHEAR (VWS). TS 06W IS TRACKING ALONG THE
WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. THE FORECAST TRACK HAS SHIFTED TO THE EAST ABOUT 115 NM CLOSER
TO KADENA AB AT TAU 36, HOWEVER, THERE IS NO CHANGE TO THE OVERALL
FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 06W WILL CONTINUE TRACKING GENERALLY POLEWARD THROUGH THE
NEXT 72 HOURS AS IT FOLLOWS THE PERIPHERY OF THE STR. SLOW
INTENSIFICATION IS EXPECTED AS THE SYSTEM ENTERS AN AREA OF MORE
FAVORABLE VWS. THE PEAK INTENSITY OF 50 KTS IS EXPECTED AROUND TAU
48. NUMERICAL MODEL TRACK GUIDANCE HAS HIGH SPREAD AFTER TAU 36,
PRIMARILY DUE TO TWO MEMBERS THAT REPRESENT THE WESTERN (ECMWF
ENSEMBLE MEAN) AND EASTERN (GFS) OUTLIERS. THE BULK OF THE GUIDANCE
ALIGNS WELL WITH THE CONSENSUS TRACK. THE JTWC TRACK FORECAST
CLOSELY FOLLOWS THE CONSENSUS TRACK BUT CONFIDENCE IS LOW DUE TO THE
HIGH SPREAD IN THE MODEL GUIDANCE, A RELATIVELY WEAK AND RE-
ORIENTING SUBTROPICAL STEERING RIDGE, AND HIGH UNCERTAINTY IN THE
POSITION OF THE LLCC AS THE MONSOON DEPRESSION CONSOLIDATES.
  C. IN THE EXTENDED RANGE, TS 06W IS EXPECTED TO TURN NORTHEASTWARD
AND SLOWLY UNDERGO EXTRATROPICAL TRANSITION AS IT ENCOUNTERS A MID-
LATITUDE TROUGH. SLIGHT WEAKENING IS ANTICIPATED, ALTHOUGH
BAROCLINIC INTERACTION WITH THE TROUGH SHOULD ALLOW THE SYSTEM TO
MAINTAIN GALE FORCE OR STRONGER WINDS THROUGHOUT THE TRANSITION. THE
MODEL TRACKERS DEPICT A HIGHLY UNCERTAIN STORM TRACK IN THE EXTENDED
PERIOD, SO CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC FORECAST
TRACK IS LOW.//
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