Advisories

WDPN32 PGTW 161500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (CHAMPI) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.4N 151.4E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 405 NM EAST-SOUTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 29W IS POISED TO RAPIDLY INTENSIFY AND IS
APPROACHING TYPHOON STRENGTH. FOLLOWING THE COMPACT CYAN RING
FEATURE DEPICTED IN THE 160611Z GMI 37 GHZ IMAGE, A TRANSIENT WARM
SPOT BRIEFLY APPEARED IN ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY. SINCE THEN, EXPLOSIVE CONVECTION HAS FORMED ALONG THE
EASTERN PERIPHERY, OBSCURING THE WARM SPOT, WHILE A LARGE BANDING
FEATURE PERSISTS WEST OF THE STORM CENTER. A 161145Z ASCAT-C PASS
REVEALS IMPROVED SYMMETRY OF THE LOW-LEVEL CIRCULATION BUT LIKELY
UNDERSAMPLED THE MAXIMUM WINDS WITHIN THE VERY COMPACT INNER CORE.
THE SYSTEM IS LOCATED OVER WARM SEA SURFACE TEMPERATURES (SST) OF
29-30 DEGREES CELSIUS AND HIGH OCEAN HEAT CONTENT (OHC) OF NEAR 100
KJ PER CM2. THESE FACTORS, ALONG WITH STRONG WESTWARD OUTFLOW AND
10-15 KTS OF VERTICAL WIND SHEAR (VWS), ARE FAVORABLE FOR CONTINUED
INTENSIFICATION. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE SCATTEROMETER DATA AND TIGHTLY CURVED
CONVECTIVE BANDING. THE INITIAL INTENSITY IS SET AT 60 KTS WITH
MEDIUM CONFIDENCE BASED ON THE MARKEDLY IMPROVED CONVECTIVE
STRUCTURE AND A BLEND OF THE T3.5 AND T4.0 SUBJECTIVE DVORAK
CLASSIFICATIONS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR 29N 160E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS ADT: 57 KTS AT 161110Z
   CIMSS AIDT: 52 KTS AT 161110Z
   CIMSS D-MINT: 63 KTS AT 160540Z
   CIMSS D-PRINT: 43 KTS AT 161040Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG WESTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST TRACK HAS SHIFTED
SOUTHWARD BY APPROXIMATELY 15 NM AT TAUS 24 AND 36.

FORECAST DISCUSSION: TS 29W IS BEING STEERED WESTWARD BY A
WEAKENING STR TO THE NORTHEAST. IN THE NEXT 24 HOURS, A SHARP
TROUGH APPROACHING THE KOREAN PENINSULA WILL SUPPORT THE
DEVELOPMENT OF A NEW RIDGE OVER HONSHU. THE NEW STR WILL QUICKLY
BUILD EASTWARD, MAINTAINING A WEST TO WEST-NORTHWESTWARD MOTION
THROUGH TAU 60. THEREAFTER, THE SYSTEM WILL ROUND THE SOUTHWESTERN
PERIPHERY OF THE RIDGE AND TURN NORTHWESTWARD. THE ENVIRONMENT WILL
REMAIN FAVORABLE FOR THE NEXT FEW DAYS, WITH TS 29W TRAVERSING SST
OF 29-30 DEGREES CELSIUS UNDER LOW TO MODERATE VWS. WITH A CLOSED
INNER CORE NOW ESTABLISHED, THE SYSTEM IS LIKELY ENTERING A
PROLONGED EPISODE OF RAPID INTENSIFICATION (RI). THE FORECAST CALLS
FOR TS 29W TO ATTAIN TYPHOON STRENGTH SHORTLY, FOLLOWED BY A
PASSAGE OVER OR VERY NEAR GUAM WITH MAXIMUM SUSTAINED WINDS NEAR
100 KTS. THE STRONGEST WINDS WILL REMAIN CONFINED TO A SMALL AREA
NEAR THE CENTER, WHILE THE GALE-FORCE WIND RADII EXTEND NORTHWARD
TO TINIAN AND SAIPAN. AFTER TAU 60, VWS WILL EASE TO 5-10 KTS AS
THE SYSTEM MOVES OVER EVEN WARMER SST OF 30-31 DEGREES CELSIUS AND
OHC VALUES OF 120-140 KJ PER CM2. HOWEVER, BY THIS TIME,
DIFFICULT-TO-PREDICT INTERNAL TROPICAL CYCLONE DYNAMICS MAY CAUSE
THE INTENSITY TO LEVEL OFF OR WEAKEN. THE WIND FIELD WILL GRADUALLY
EXPAND AS IT PASSES THE SOUTHERN MARIANA ISLANDS.

MODEL DISCUSSION: TRACK GUIDANCE IS IN EXCELLENT AGREEMENT THROUGH
TAU 36 WITH A CROSS-TRACK SPREAD OF 35 NM AMONG THE CORE MODEL
GROUP NEAR THE CPA TO GUAM. THE CROSS-TRACK SPREAD INCREASES TO 150
NM BY TAU 72. THE GUIDANCE SUITE HAS SHIFTED SOUTHWARD YET AGAIN,
WITH THE BULK OF THE DYNAMICAL AND AI MODELS TAKING THE CENTER OF
TS 29W SOUTH OF GUAM. GOOGLE DEEPMIND DEPICTS A PASSAGE 30 NM SOUTH
OF GUAM. HAFS-A AND JGSM ARE THE ONLY SOLUTIONS THAT BRING THE
SYSTEM OVER OR JUST NORTH OF GUAM. THEREFORE, THE JTWC FORECAST
TRACK HAS BEEN ADJUSTED SOUTHWARD YET AGAIN, NOW POSITIONED ALONG
THE NORTHERN SIDE OF THE GUIDANCE ENVELOPE. FURTHER SOUTHWARD
ADJUSTMENTS MAY BE NECESSARY IF CURRENT TRENDS CONTINUE. ONCE
AGAIN, THE INTENSITY GUIDANCE HAS TRENDED STRONGER. HAFS-A AND
DEEPMIND DEPICT CONTINUED RI THROUGH TAU 48, WITH PEAK INTENSITIES
OF 150 KTS AND 140 KTS, RESPECTIVELY, AROUND TAU 60-72. NEAR THE
CPA TO GUAM, THE MOST INTENSE SOLUTIONS REACH UP TO 120 KTS. MOST
OF THE GUIDANCE SHOWS THE INTENSITY LEVELING OFF OR WEAKENING
BEYOND TAU 72. THE JTWC INTENSITY FORECAST LIES NEAR THE HIGH END
OF THE GUIDANCE ENVELOPE, ALIGNING WITH DEEPMIND THROUGH TAU 48 BUT
REMAINING LOWER FROM TAU 60 TO TAU 120.

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