The new peak intensity is 120kt.
12 HRS, VALID AT:
180600Z --- 18.3S 76.2E
MAX SUSTAINED WINDS - 120 KT, GUSTS 145 KT
WDXS31 PGTW 172100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (DJOUNGOU) WARNING
NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
INITIAL POSITION: 16.7S 72.3E
INITIAL INTENSITY: 100 KTS
GEOGRAPHIC REFERENCE: 576 NM SOUTH OF DIEGO GARCIA
MOVEMENT PAST 6 HOURS: EASTWARD AT 19 KTS
SIGNIFICANT WAVE HEIGHT: 36 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THAT THE
VORTEX ASSOCIATED WITH TROPICAL CYCLONE (TC) 13S HAS UNDERGONE
AXISYMMETRIZATION AND BECOME VERTICALLY ALIGNED, WITH A STRONG EYE
EMERGING IN THE EIR WITHIN THE LAST 2 HOURS, MARKING THE ONSET OF
FORECASTED PERIOD OF RAPID INTENSIFICATION (RI). A 171639Z
TROPICS-6 91GHZ MICROWAVE IMAGER REVEALED A WELL-DEFINED MICROWAVE
FEATURE, SURROUNDED BY MODERATELY STRONG DEEP CONVECTION, FORMING A
SYMMETRICAL EYEWALL. A VERY SMALL AMOUNT OF VERTICAL TILT DOWNSHEAR
TOWARDS THE SOUTH-SOUTHEAST IS EVIDENT IN THE HIGHER FREQUENCY
TROPICS CHANNELS, CONFIRMING THE STRUCTURE SEEN IN THE
HIGH-RESOLUTION MODEL FIELDS. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE OBSERVABLE EYE IN THE INFRARED
IMAGERY, AND EXTRAPOLATION OF THE MICROWAVE EYE IN THE TROPICS
IMAGERY NOTED ABOVE. THE INITIAL INTENSITY OF 100 KTS IS PLACED
WITH MEDIUM CONFIDENCE, CONSISTENT WITH SUBJECTIVE DVORAK ESTIMATES
FROM 4.5 TO 5.5 (77-102 KTS) FROM MULTIPLE AGENCIES. ANALYSIS
REVEALS A FAVORABLE ENVIRONMENT, WITH WARM SSTS, LOW DEEP-LAYER VWS
AND ROBUST POLEWARD OUTFLOW INTO THE DIVERGENT ENTRANCE REGION OF A
130 KNOT JET MAX TO THE SOUTHEAST, WHICH IS THE MAIN FACTOR IN THE
RAPID INTENSIFICATION OF THE SYSTEM.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: NEAR EQUATORIAL RIDGE (NER) TO THE
NORTHEAST.
AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T5.5 - 102 KTS
KNES: T5.5 - 102 KTS
DEMS: T5.0 - 90 KTS
FMEE: T5.0 - 90 KTS
FIMP: T4.5 - 77 KTS
CIMSS SATCON: 111 KTS AT 171930Z
CIMSS ADT: 104 KTS AT 171930Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
VWS: 10-15 KTS
SST: 29-30 CELSIUS
OUTFLOW: STRONG POLEWARD
ANALYSIS CONFIDENCE:
INITIAL POSITION: HIGH
INITIAL INTENSITY: MEDIUM
INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TC 13S IS CURRENTLY TRACKING JUST A SHADE
SOUTH OF DUE EAST, ALONG THE NER TO THE NORTH, WHICH EXTENDS ALL
THE WAY TO AUSTRALIA. NO SIGNIFICANT CHANGE IN THE STEERING PATTERN
IS EXPECTED, OTHER THAN A SLIGHT REORIENTATION OF THE RIDGE AXIS.
THIS WILL PUSH TC 13S ONTO A MORE SOUTHEASTWARD TRACK AFTER TAU 12,
WHICH WILL CONTINUE THROUGH THE REMAINDER OF THE FORECAST, AS
THE SYSTEM TRACKS INTO THE MIDLATITUDES. THROUGH TAU 36, TC 13S IS
FORECASTED TO CONTINUE TO RAPIDLY INTENSIFY, EXPECTED TO REACH A
PEAK INTENSITY OF AT LEAST 120 KTS AT TAU 12. AFTER REACHING ITS
PEAK, THE SYSTEM WILL BEGIN TO WEAKEN SLOWLY AT FIRST, BUT AFTER
TAU 36 TC 13S WILL BEGIN TO RAPIDLY WEAKEN AS NORTHWESTERLY SHEAR
INCREASES SHARPLY AND PULLS IN DRY AIR WHICH WILL ENTRAIN INTO THE
CORE OF THE SYSTEM. TC 13S IS FORECASTED TO BEGIN SUBTROPICAL
TRANSITION (STT) AT TAU 36 AND BY TAU 48, THE SYSTEM WILL BE
DECAPITATED BY THE STRONG SHEAR AND SMOTHERED BY A DEEP LAYER OF
DRY AIR ABOVE 700MB. STT IS FORECAST TO BE COMPLETE NO LATER THAN
TAU 72, BUT POTENTIALLY AS EARLY AS TAU 48.
MODEL DISCUSSION: MODEL GUIDANCE CONTINUES TO BE IN TIGHT AGREEMENT
DUE TO A VERY SIMPLE STEERING MECHANISM. THE JTWC TRACK FORECAST IS
PLACED WITH HIGH CONFIDENCE WITH A CROSS-TRACK SPREAD AT TAU 72 OF
JUST 100 NM. INTENSITY GUIDANCE HAS A BIT MORE SPREAD WITH MOST
GUIDANCE SHOWING THE SAME GENERAL TREND THROUGHOUT THE FORECAST
PERIOD. PEAK INTENSITY IN THE GUIDANCE RANGES FROM 110 KNOTS FOR
THE SHIPS MODEL, UP TO 135 KNOTS FOR THE COAMPS-TC ENSEMBLE MEAN
(CTR1) WITH THE JTWC FORECAST MOST CLOSELY FOLLOWING THE HAFS-A
GUIDANCE THROUGH TAU 36. FOR THE REMAINDER OF THE FORECAST PERIOD,
THE GUIDANCE PACKAGE IS IN GOOD AGREEMENT WITH WEAKENING AFTER TAU
24, BUT WITH A 20 KT SPREAD THROUGH TO THE END OF FORECAST PERIOD.
FOR THIS REASON, THE JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM
CONFIDENCE.
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