Tropical Storm SONGDA Advisory 7月29日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (SONGDA)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 28.0N 133.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 332 NM EAST-NORTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS BROAD DEEP
FLARING CONVECTION THAT HAS BEGUN TO BECOME BETTER CONSOLIDATED,
BUT AS OF YET LACKS A DISTINCTIVE OR CLEAR LOW LEVEL CIRCULATION
CENTER (LLCC), AS THE SYSTEM IS EMBEDDED IN THE NORTHEASTERN
PERIPHERY OF A MONSOON GYRE. A 282206Z SSMIS 37GHZ MICROWAVE PASS
INDICATES A CYCLONICALLY CURVED BAND OF DEEP CONVECTION ALONG THE
SOUTHERN SIDE OF THE SYSTEM, WRAPPING WEAKLY UP TO THE EAST SIDE.
RECENT SCATTEROMETER DATA SUGGESTS THAT THE HIGHEST WINDS ARE
CONFINED TO THE NORTHERN PERIPHERY OF THE SYSTEM, IN A BAND THAT
EXTENDS TO THE EAST AND SOUTHEAST. THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED VISIBLE IMAGERY AND
THE AFOREMENTIONED MICROWAVE IMAGE. THE INITIAL INTENSITY OF 30
KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A COMBINATION OF
RECENT SCATTEROMETERY DATA, AND IS SLIGHTLY HIGHER THAN THE PGTW
T1.0 FIX BUT IN LINE WITH THE RJTD T2.0 FIX. ENVIRONMENTAL ANALYSIS
INDICATES THE SYSTEM IS IN A OVERALL FAVORABLE AREA FOR DEVELOPMENT
WITH WARM SEA SURFACE TEMPERATURES (28-29C), LOW (10-15
KNOTS) VERTICAL WIND SHEAR, AND DIFFLUENT EASTERLY FLOW ALOFT WITH A
WEAK POLEWARD OUTFLOW CHANNEL.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A LOW TO
MID-LEVEL SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.0 - 25 KTS
   RJTD: T2.0 - 30 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.
FORECAST DISCUSSION: TD 06W HAS GENERALLY TRACKED TO THE NORTHWEST
OVER THE PAST 6-12 HOURS UNDER THE INFLUENCE OF A STR CENTERED TO
THE EAST. HOWEVER THE STEERING PATTERN IS IN FLUX, AS A LOW TO
MID-LEVEL STR HAS DEVELOPED TO THE NORTH OVER THE SEA OF JAPAN, AND
WILL RESTRICT MUCH IN THE WAY OF POLEWARD MOVEMENT GOING FORWARD.
THUS, TD 06W IS FORECAST TO TRACK GENERALLY WEST-NORTHWEST, TURNING
NEARLY DUE WEST BY TAU 24 AS THE ORIENTATION OF THE STEERING RIDGE
SHIFTS AND BUILDS IN TO THE WEST ACROSS THE NORTHERN SIDE OF THE
SYSTEM. THE FORECAST CALLS FOR LITTLE IN THE WAY OF
INTENSIFICATION. WHILE THE ENVIRONMENTAL CONDITIONS ARE FAVORABLE
FOR DEVELOPMENT, THE MAIN INHIBITING FACTOR WILL BE THE LACK OF A
WELL-DEFINED LLCC AND THE FACT THAT THE SYSTEM LIES ALONG THE
NORTHERN PERIPHERY OF THE MONSOON GYRE WHICH IS SLOWING THE
CONSOLIDATION OF THE LOW LEVEL CORE. TD 06W WILL MAINTAIN ITS
INTENSITY FOR THE FIRST 24 HRS BEFORE WEAKENING BY TAU 36 AS IT
APPROACHES COASTAL CHINA, AND IS EXPECTED TO MAKE LANDFALL IN THE
VICINITY OF SHANGHAI BETWEEN TAU 36 AND TAU 48 AND DISSIPATE
SHORTLY THEREAFTER.
MODEL DISCUSSION: LIMITED TRACK GUIDANCE WAS AVAILABLE FOR THIS
FORECAST RUN, BUT ANALYSIS OF MODEL FIELDS AND ENVIRONMENTAL
PARAMETERS PROVIDE MEDIUM OVERALL CONFIDENCE IN THE TRACK AND THE
FORECAST TRACK LIES TO THE SOUTH OF WHAT LIMITED TRACK GUIDANCE WAS
AVAILABLE, CLOSE TO THE ECMWF INTERMEDIATE TRACKER. UNFORTUNATELY,
THERE WAS NO INTENSITY GUIDANCE AVAILABLE FOR THIS RUN AND SO THE
INTENSITY FORECAST IS BASED SOLELY ON PERSISTENCE AND ENVIRONMENTAL
ANALYSIS, WITH LOW CONFIDENCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: LOW//
NNNN
NNNN