WDXS32 PGTW 290300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 22S (HALIMA) WARNING 
NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.9S 82.4E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 1040 NM SOUTH-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT
SYSTEM, WITH A CONVECTIVE STRUCTURE WHICH HAS BEEN RELATIVELY
STABLE OVER THE PAST SIX TO TWELVE HOURS. A 282257Z SSMIS 37GHZ
MICROWAVE IMAGE SHOWED A CYCLONICALLY CURVED REGION OF CURVED
CONVECTION ALONG THE SOUTHERN PERIPHERY OF THE WELL DEFINED LOW
LEVEL CIRCULATION CENTER (LLCC), AND LENT HIGH CONFIDENCE TO THE
INITIAL POSITION. THE SYSTEM IS UNDER SOME WESTERLY SHEAR, WHICH IS
IMPARTING SOME PRESSURE ON THE WESTERN SIDE OF THE CIRCULATION.
ADDITIONALLY, DRY AND RELATIVELY STABLE AIR IS SOLIDLY IN PLACE
ALONG THE WESTERN PERIPHERY AS INDICATED BY THE LARGE FIELD OF
STABLE STRATOCUMULUS IN THE WESTERN HEMISPHERE OF THE CIRCULATION.
EVEN IN THE FACE OF THE SHEAR AND DRY AIR, THE SYSTEM HAS BEEN ABLE
TO MAINTAIN A CONSISTENT INTENSITY OF 45 KNOTS, BASED ON THE
CONGLOMERATION OF AGENCY DVORAK CURRENT INTENSITY ESTIMATES AT T3.0
(45 KNOTS) AND THE SATCON ESTIMATE OF 46 KNOTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHERN SIDE OF AN EXTENSION OF THE
NEAR EQUATORIAL RIDGE (NER), WHICH LIES ALONG THE 25TH LATITUDE
LINE, EXTENDING NORTHWEST TO A RIDGE CENTER NEAR 10S 65E. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   FMEE: T3.0 - 45 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS SATCON: 46 KTS AT 281919Z
   CIMSS ADT: 33 KTS AT 282115Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE EASTWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR INTRUSION IN THE MID AND
UPPER-LEVELS

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE OVERALL DISSIPATION PHILOSOPHY
HAS NOT CHANGED, HOWEVER THE FORECAST HAS BEEN LENGTHENED TO CARRY
THE SYSTEM LATER INTO THE FORECAST PERIOD BEFORE DISSIPATION
OCCURS. 

FORECAST DISCUSSION: TC 22S HAS OVER THE PAST TWELVE HOURS TURNED
FIRST EAST AND NOW EAST-NORTHEAST, AS THE LOW TO MID-LEVEL RIDGE
BUILDS IN TO THE SOUTH OF THE SYSTEM. OVERALL HOWEVER, THE STEERING
PATTERN IS RELATIVELY WEAK AND THE OVERALL TRACK MOTION, WHILE
GENERALLY TOWARDS THE NORTH, IS FRAUGHT WITH UNCERTAINTY. THE RIDGE
EXTENSION TO THE SOUTH IS EXPECTED TO PUSH NORTHWARD OVER THE NEXT
12 TO 24 HOURS, ALLOWING FOR TC 22S TO MOVE NORTH WITH IT. HOWEVER,
THE RIDGE WILL ERODE QUICKLY AHEAD OF AN APPROACHING TROUGH AND BY
TAU 36, TC 22S WILL LIE IN A COL REGION BETWEEN THE TROUGH TO THE
SOUTH, AND NEAR EQUATORIAL RIDGE CENTERS TO THE EAST AND WEST. THE
NET EFFECT WILL BE A SLOW DRIFT GENERALLY NORTHWARD AT A VERY SLOW
THREE KNOTS OR LESS. SHEAR HAS DECREASED OVER THE PAST TWELVE
HOURS, DOWN TO MORE MODERATE LEVELS, WHICH HAS ALLOWED THE SYSTEM
TO MAINTAIN ITS STRUCTURE AND INTENSITY, EVEN IN THE FACE OF THE
SIGNIFICANT DRY AIR TO THE WEST. AS THE SYSTEM TRACKS NORTHWARD IT
WILL MOVE UNDER THE UPPER-LEVEL RIDGE, WITH AN ACCOMPANYING
REDUCTION OF THE OVERALL SHEAR. BUT THE CONTINUED INTRUSION OF VERY
DRY AND STABLE AIR PROGRESSIVELY FURTHER INTO THE CORE OF THE
SYSTEM AND THE REDUCED OUTFLOW WILL OFFSET THE REDUCED SHEAR AND
LEAD TO A LONG AND SLOW DISSIPATION. THE SYSTEM IS EXPECTED TO
DISSIPATE TO BELOW WARNING CRITERIA NO LATER THAN TAU 72.   

MODEL DISCUSSION: ENSEMBLE AND DETERMINISTIC TRACK GUIDANCE IS IN
RELATIVELY GOOD AGREEMENT ON THIS RUN, SHOWING A SIGNIFICANT
CONSOLIDATION OVER THE PREVIOUS RUN. WITH THE EXCEPTION OF NAVGEM,
ALL THE AVAILABLE GUIDANCE CONCURS ON A GENERALLY NORTHWARD TRACK,
WITH THE GFS, GFS ENSEMBLE AND ECMWF ON THE WESTERN EDGE OF THE
ENVELOPE AND THE EGRR AND GALWEM TRACKERS ON THE EASTERN SIDE.
THROUGH THE FORECAST DURATION, THE SPREAD STEADILY INCREASES TO 200
NM AT TAU 72. THE ECENS AND GEFS MEANS ARE IN CLOSE AGREEMENT, BUT
THE ECENS IN PARTICULAR SHOWS A WIDE SPREAD OF ENSEMBLE MEMBERS,
WITH A SIGNIFICANT NUMBER TRACKING THE SYSTEM FAR TO THE EAST. THE
JTWC FORECAST LIES CLOSE TO THE CONSENSUS MEAN WITH MEDIUM
CONFIDENCE. INTENSITY GUIDANCE IS MIXED, WITH THE HWRF AND
COAMPS-TC BEING THE MOST BEARISH, INDICATING DISSIPATION WITHIN 24
HOURS, WHILE THE DECAY SHIPS SHOWS THE SYSTEM MAINTAINING INTENSITY
TO TAU 72, THEN DISSIPATION BY TAU 96. INTERESTINGLY, THE ECENS
MEMBERS TAKING THE SYSTEM TO THE EAST INDICATE A MUCH STRONGER
SYSTEM, WHILE THOSE MEMBERS TO THE WEST INDICATE A WEAKER, SUB-TS
LEVEL SYSTEM. THE JTWC FORECAST IS CLOSE TO THE CONSENSUS MEAN
THROUGH TAU 48, THEN IS BELOW THE MEAN THROUGH THE REMAINDER OF THE
FORECAST WITH LOW CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: LOW//
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