Advisories

WDPN32 PGTW 020900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SAUDEL) WARNING 
NR 044//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.3N 117.4E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 178 NM EAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION 17W (SAUDEL) WITH A LOOSELY-DEFINED LOW-LEVEL CIRCULATION 
CENTER (LLCC) AND BURSTS OF CONVECTION FORMING TO THE NORTHWEST, ALONG 
THE COAST OF CHINA. A PARTIAL 020228Z METOP-C ASCAT PASS REVEALED A 
BROAD WIND MINIMUM REGION ASSOCIATED WITH THE LLCC. THE INITIAL 
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE ANIMATED MSI AND 
EXTRAPOLATION FROM THE ASCAT PASS. THE INITIAL INTENSITY OF 30 KTS IS 
ASSESSED WITH HIGH CONFIDENCE BASED ON THE ASCAT PASS AND VARIOUS 
SURFACE OBSERVATIONS WITHIN THE SOUTH CHINA SEA. ENVIRONMENTAL 
ANALYSIS INDICATES THAT 17W IS NOW IN A MARGINAL ENVIRONMENT 
CHARACTERIZED BY WEAK OUTFLOW ALOFT, LOW TO MODERATE (15-20 KTS) 
EASTERLY VERTICAL WIND SHEAR, PROXIMITY TO LAND, AND WARM (29-30 C) 
SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: THE NORTHERN PERIPHERY OF A NEAR 
EQUATORIAL RIDGE (NER) POSITIONED TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 38 KTS AT 020515Z
   CIMSS ADT: 35 KTS AT 020540Z
   CIMSS AIDT: 36 KTS AT 020540Z
   CIMSS D-MINT: 31 KTS AT 020516Z
   CIMSS D-PRINT: 37 KTS AT 020540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK POLEWARD AND EQUATORWARD
   OTHER FACTORS: PROXIMITY TO THE COAST OF CHINA

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE 
FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 17W (SAUDEL) IS FORECAST TO BEGIN SLOWING 
TRACK SPEEDS OVER THE NEXT 12 HOURS AS THE STEERING PATTERN BECOMES 
MUCH WEAKER DUE TO THE NER TO THE SOUTH MOVING OFF TO THE WEST. 17W IS 
FORECAST TO DRIFT NORTHEASTWARD FOR ONLY ANOTHER 12 HOURS BEFORE 
TURNING WESTWARD ONCE A SUBTROPICAL RIDGE (STR) BUILDS OVER EASTERN
CHINA AND ASSUMES STEERING OVER THE SYSTEM. LANDFALL ALONG THE COAST 
OF CHINA IS FORECAST TO OCCUR RIGHT AROUND TAU 24. A WESTWARD TRACK 
ALONG THE SOUTHERN PERIPHERY OF THE STR IS THEN EXPECTED TO PERSIST 
THROUGH THE REMAINDER OF THE FORECAST PERIOD. REGARDING INTENSITY, 17W 
IS FORECAST TO MAINTAIN ITS CURRENT INTENSITY THROUGH TAU 24 AS THE 
VORTEX REMAINS OVER THE WARM WATERS. AFTER TAU 24, TERRAIN INTERACTION 
WILL WEAKEN THE VORTEX WITH DISSIPATION FORECAST TO OCCUR AROUND TAU 
60, NORTH OF HONG KONG. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT ON THE
WESTWARD TURN WITH THE EXCEPTION OF NAVGEM, WHICH KEEPS THE VORTEX 
JUST OFF THE COAST ALL THE WAY THROUGH TAU 60. THE JTWC TRACK FORECAST 
IS PLACED NEAR THE MODIFIED CONSENSUS THROUGHOUT THE FORECAST PERIOD 
WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE AGREES ON A STEADY 
INTENSITY THROUGH TAU 24 FOLLOWED BY WEAKENING. AS A RESULT, THE JTWC 
INTENSITY FORECAST IS PLACED NEAR THE CONSENSUS WITH HIGH CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: HIGH//
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