Advisories

WDPN31 PGTW 190900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SAUDEL) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.5N 154.1E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 144 NM EAST-NORTHEAST OF CHUUK
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL STORM 
(TS) 17W (SAUDEL) WITH A MOSTLY OBSCURED LOW-LEVEL CIRCULATION CENTER 
(LLCC) THAT IS ELONGATED IN THE NORTH-SOUTH DIRECTIONS. DEEP 
CONVECTION WAS PRESENT WITHIN THE SOUTHERN SEMICIRCLE UP UNTIL 
190500Z, AROUND THE TIME OF THE DIURNAL CONVECTIVE MINIMUM FOR THE 
AREA. A 190305Z AMSR2 89 GHZ MICROWAVE IMAGE REVEALED A DEFINED BAND 
OF DEEP CONVECTION ALONG THE SOUTHWESTERN QUADRANT WRAPPING INTO THE 
CENTER AND LOOSE LOW-LEVEL CLOUD LINES WITHIN THE NORTHERN SEMICIRCLE. 
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON LOW-
LEVEL CLOUD TRACING IN ANIMATED MSI AND THE AMSR2 MICROWAVE IMAGE. THE 
INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED 
ON THE AGENCY DVORAK AND CIMSS INTENSITY ESTIMATES LISTED BELOW. 
ENVIRONMENTAL CONDITIONS ARE NOW ASSESSED TO BE FAVORABLE, 
CHARACTERIZED BY STRONG EQUATORWARD OUTFLOW ALOFT, LOW (10-15 KTS) 
NORTHEASTERLY VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE 
TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN, PRIMARILY DRIVEN
BY A NEAR EQUATORIAL RIDGE (NER) POSITIONED TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 30 KTS AT 190540Z
   CIMSS ADT: 37 KTS AT 190610Z
   CIMSS AIDT: 36 KTS AT 190610Z
   CIMSS D-MINT: 28 KTS AT 190305Z
   CIMSS D-PRINT: 28 KTS AT 190610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: SLIGHT DRY AIR ENTRAINMENT FROM THE NORTH

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 17W (SAUDEL) HAS STARTED TO TRACK SLOWLY
NORTHWARD OVER THE PAST 6 HOURS, PRIMARILY UNDER THE INFLUENCE OF A 
NER POSITIONED TO THE SOUTHEAST. TRACK SPEEDS ARE EXPECTED TO INCREASE 
OVER THE NEXT 12 HOURS AS THE SUBTROPICAL RIDGE (STR) CURRENTLY 
POSITIONED SOUTH OF HONSHU WEAKENS AND RETREATS NORTHWARD, LETTING 17W 
GAIN LATITUDE. SIMULTANEOUSLY, A SEPARATE STR TO THE NORTHEAST IS 
EXPECTED TO BUILD AND EXTEND SOUTHWESTWARD, BECOMING THE PRIMARY 
STEERING MECHANISM THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD. 
THE CPA TO SAIPAN CONTINUES TO BE AROUND 140 NM OCCURRING AT 220600Z. 
THE TRAJECTORY IS FORECAST TO BECOME MORE WEST-NORTHWESTWARD AFTER TAU 
72 AS RIDGING EXTENDS TO THE NORTH OF 17W. THE ENVIRONMENT IS FORECAST 
TO IMPROVE OVER THE NEXT 12 HOURS AS THE DRY AIR ENTRAINMENT FROM THE 
NORTH LESSENS, ALLOWING FOR THE CORE OF THE VORTEX TO MOISTEN. ALONG 
WITH THE AXISYMMETRIZATION OF THE WIND FIELD, 17W IS FORECAST TO 
STEADILY INTENSIFY THROUGH TAU 48 TO AROUND 70 KTS. A MORE RAPID RATE 
OF INTENSIFICATION IS POSSIBLE DURING THIS TIME IF THE SYMMETRIZATION 
PROCESS OCCURS MORE QUICKLY. AFTER TAU 48, 17W IS FORECAST TO RAPIDLY 
INTENSIFY THROUGH TAU 72 AS THE SYSTEM TAKES ADVANTAGE OF STRONG DUAL 
CHANNEL OUTFLOW, VERY WARM (OVER 30 C) SEA SURFACE TEMPERATURES, AND 
HIGH OCEAN HEAT CONTENT (OHC) VALUES EAST OF THE MARIANAS. 17W IS THEN
FORECAST TO FURTHER INTENSIFY TO A PEAK OF AROUND 125 KTS AT TAU 96
WITH A STEADY INTENSITY THROUGH TAU 120 AS THE SYSTEM BEGINS TO ENTER 
AN AREA OF INCREASED NORTHERLY SHEAR AND LOWER OHC.

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72 
WITH NO NOTABLE OUTLIERS PRESENT. THE CROSS-TRACK SPREAD AT TAU 72 IS 
MEASURED TO BE ABOUT 100NM. AFTER TAU 72, NAVGEM BECOMES A POLEWARD 
OUTLIER, TRACKING THE VORTEX CLOSER TO IWO TO. DISCOUNTING NAVGEM, 
CROSS-TRACK SPREAD INCREASES TO 210 NM AT TAU 120. THE JTWC TRACK 
FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS THROUGH TAU 72 
AND THEN SLIGHTLY TO THE SOUTH THROUGH TAU 120 TO OFFSET NAVGEM. 
INTENSITY GUIDANCE IS IN LESS AGREEMENT THIS MODEL RUN. MULTIPLE RAPID 
INTENSIFICATION (RI) AIDS HAVE TRIGGERED, AND THEY SUGGEST A MUCH 
QUICKER RATE OF INTENSIFICATION THROUGH TAU 48. THE RI AIDS ARE 
GROUPED AROUND A 95 KNOT INTENSITY AT TAU 48 WHILE THE NON-RI AIDS 
(SUCH AS HAFS-A) ARE AROUND 55-65 KTS. GIVEN THE ASYMMETRY IN THE WIND 
FIELD, THE JTWC INTENSITY FORECAST IS PLACED CLOSER TO THE NON-RI AIDS 
THROUGH TAU 48. MODELS THEN GENERALLY AGREE ON RI THROUGH TAU 72. PEAK 
INTENSITIES RANGE FROM 105-145 KTS AT TAU 96 WITH CTR1 (COAMPS-TC RI) 
BEING THE MOST AGGRESSIVE. THE JTWC FORECAST CALLS FOR A PEAK 
INTENSITY OF 125 KTS, ON THE HIGHER END OF THE GUIDANCE ENVELOPE DUE 
TO THE EXPECTED HIGHLY FAVORABLE ENVIRONMENT EAST OF THE MARIANAS.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
NNNN