Advisories

WDPN33 PGTW 230300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 19W (NINETEEN) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.0N 135.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 266 NM NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LOW LEVEL
CIRCULATION CENTER (LLCC), NOW FULLY EXPOSED, MOVING INTO THE CLEAR
AIR TO THE EAST OF AN AREA OF WANING CONVECTION. A 230034Z ASCAT-B
PASS REVEALS AN ASYMMETRIC WIND FIELD, WITH 30 KNOT WINDS PRESENT
ALONG THE SOUTHERN EXTENT OF THE CIRCULATION, WHILE WINDS ALONG THE
NORTHERN FLANK ARE MUCH LIGHTER, IN THE 15-25 KNOT RANGE. ANIMATED
WATER VAPOR IMAGERY SHOWS A LARGE AREA OF DRY MID-LEVEL AIR PRESENT
ALONG THE EASTERN FLANK OF THE SYSTEM, AS WELL AS MODERATE TO
STRONG NORTHEASTERLY FLOW ALOFT, INDUCING BOTH SOME CONVERGENCE
UPSTREAM OF TD 19W AND MODERATE EQUATORWARD OUTFLOW. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE SUPPORTED BY THE EXPOSED
LLCC IN THE MSI AND THE ASCAT-B PASS. THE INITIAL INTENSITY IS ALSO
ASSESSED WITH HIGH CONFIDENCE BASED ON THE ASCAT-B DATA AND THE
CONGRUENCE OF THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES
NOTED BELOW. ENVIRONMENTAL CONDITIONS ARE MARGINAL, WITH THE LOW
DEEP-LAYER SHEAR AND WARM SSTS OFFSET BY THE DRY MID-LEVEL AIR TO
THE EAST AND WEAK TO MODERATE OUTFLOW ALOFT.

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

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN; THE SYSTEM IS
EMBEDDED WITHIN A TROUGH OF LOW PRESSURE EXTENDING NORTHEASTWARD TO
TY 17W, AND POSITIONED ALONG THE NORTHERN EDGE OF A BAND OF
LOW-LEVEL MONSOONAL SOUTHWESTERLIES. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 34 KTS AT 230010Z
   CIMSS ADT: 33 KTS AT 230010Z
   CIMSS AIDT: 32 KTS AT 230010Z
   CIMSS D-MINT: 27 KTS AT 222109Z
   CIMSS D-PRINT: 29 KTS AT 230010Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY MID-LEVEL AIR ALONG THE EASTERN FLANK. 

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: TROPICAL DEPRESSION (TD) 19W (NINETEEN) HAS
DRIFTED GENERALLY NORTH-NORTHWESTWARD OVER THE PAST 12 HOURS,
TRAPPED IN A WEAK STEERING PATTERN. IN THE LOWER-LEVELS, THE SYSTEM
LIES IN THE SOUTHWESTERN END OF A TROUGH WHICH EXTENDS
NORTHEASTWARD TO TY 17W, WHILE TO THE SOUTH A NEAR EQUATORIAL RIDGE
(NER) CENTERED SOUTH OF THE EQUATOR IS PRODUCING A STRONG LOW-LEVEL
GRADIENT ALONG THE SOUTHERN PERIPHERY OF TD 19W. OVER THE PAST
COUPLE OF HOURS HOWEVER, IT APPEARS THAT TD 19W MAY BE STARTING ITS
TURN NORTHEASTWARD, AS THE LOW-LEVEL SOUTHWESTERLIES PICK UP
STRENGTH. THE SYSTEM WILL GRADUALLY TURN TO A NORTHWARD TRACK BY
TAU 36, DECELERATE, THEN TURN NORTHWESTWARD AS THE STR TO THE NORTH
ASSUMES THE PRIMARY STEERING INFLUENCE. WHILE SHEAR IS EXPECTED TO
REMAIN LOW FOR THE NEXT 24 HOURS, THE PRESENCE OF DRY MID-LEVEL AIR
WILL INHIBIT CONVECTIVE CONSOLIDATION, AND THE SYSTEM IS UNLIKELY
TO INTENSIFY, THOUGH A BRIEF BURST OF CONVECTION DURING A DIURNAL
CONVECTIVE MAXIMUM COULD RESULT IN THE SYSTEM BRIEFLY REACHING
TROPICAL STORM STRENGTH. HOWEVER, EVEN IF THIS OCCURS, IT WILL BE
SHORT LIVED AS SHEAR WILL INCREASE SHARPLY AFTER TAU 18, AND REMAIN
ELEVATED THROUGH THE REMAINDER OF THE FORECAST PERIOD, LEADING TO A
SLOW BUT STEADY WEAKENING THROUGH DISSIPATION AT TAU 60. 

MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN STRONG AGREEMENT
THROUGH THE FORECAST PERIOD, WITH ALL MEMBERS OF THE TRACK
CONSENSUS SAVE FOR NAVGEM, CONFINED TO A 150NM WIDE TRACK ENVELOPE.
ALONG-TRACK SPREAD INCREASES AFTER TAU 48 AS THE SYSTEM CURVES
NORTHWESTWARD, BUT REMAINS MODEST. THE JTWC FORECAST IS POSITIONED
NEAR THE EXPERIMENTAL GOOGLE DEEPMIND TRACKER WITH HIGH CONFIDENCE.
INTENSITY GUIDANCE IS CONSISTENT WITH THE PREVIOUS RUN, WITH ALL
BUT THE CTCX TRACKER INDICATING A FLAT INTENSITY TREND THROUGH TAU
24 FOLLOWED BY STEADY WEAKENING. 

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