WDIO31 PGTW 302100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02A (ASNA) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.4N 66.4E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 90 NM SOUTH-SOUTHWEST OF KARACHI, PAKISTAN
   MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 02A (ASNA) WITH CONVECTION WRAPPING AROUND THE SOUTHERN AND
EASTERN PERIPHERIES WITH NORTHEASTERLY VERTICAL WIND SHEAR (VWS)
CAUSING THE CONVECTION TO BE BLOWN OFF SOUTHWARD. THE COMBINATION
OF THE VWS AND DRY AIR TO THE NORTH IS PREVENTING CONVECTION FROM
BUILDING OVER THE CENTER LEAVING THE LOW-LEVEL CIRCULATION CENTER
(LLCC) PARTIALLY EXPOSED. ENVIRONMENTAL ANALYSIS INDICATES THAT 02A
IS IN A MARGINALLY FAVORABLE ENVIRONMENT FOR FURTHER DEVELOPMENT
CHARACTERIZED BY STRONG EQUATORWARD OUTFLOW ALOFT, MODERATE VWS, THE
PRESENCE OF DRY AIR, AND WARM SEA SURFACE TEMPERATURES. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION
FROM THE 301631Z ASCAT-C IMAGE. THE INITIAL INTENSITY OF 40 KTS IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE SAME ASCAT-C IMAGE AND
THE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: THE SOUTHWESTERN PERIPHERY OF AN
EXTENSION OF A SUBTROPICAL RIDGE (STR) TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   DEMS: T2.5 - 35 KTS
   CIMSS SATCON: 42 KTS AT 301800Z
   CIMSS ADT: 33 KTS AT 301800Z
   CIMSS DPRINT: 40 KTS AT 301800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE NORTH.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 02A IS FORECASTED TO CONTINUE TRACKING
WESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE STR TO THE
NORTHEAST THROUGH TAU 24. AFTER TAU 24, RIDGING TO THE NORTHWEST
WILL TAKE OVER AS THE MAIN STEERING MECHANISM, CAUSING THE SYSTEM
TO TRACK MORE SOUTHWESTWARD THROUGH THE REMAINDER OF THE FORECAST
PERIOD. REGARDING INTENSITY, 02A IS EXPECTED TO REMAIN IN A
MARGINALLY FAVORABLE ENVIRONMENT DUE TO THE VWS AND DRY AIR CAUSING
MINIMAL INTENSIFICATION. AS A RESULT, 02A IS FORECAST TO MAINTAIN
40 KTS THROUGH TAU 12 WITH A SLIGHT INCREASE TO 45 KTS AT TAU 24 AS
THE SYSTEM TRACKS FURTHER FROM THE LAND TO ITS EAST. AFTER TAU 24,
02A IS ANTICIPATED TO BEGIN A WEAKENING TREND IN RESPONSE TO
INCREASING VWS AND DRY AIR ENTRAINMENT. WEAKENING TO TROPICAL
DEPRESSION STRENGTH IS EXPECTED TO OCCUR NEAR TAU 48. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
WITH THE EXCEPTION OF NAVGEM, WHICH TRACKS THE SYSTEM STRAIGHT
WESTWARD VICE THE SOUTHWESTWARD TURN THAT THE REMAINDER OF GUIDANCE
SUGGESTS. DISREGARDING NAVGEM, THERE IS A 70 NM CROSS TRACK SPREAD
AT TAU 48. THE JTWC TRACK FORECAST IS PLACED SLIGHTLY SOUTHEAST OF
CONSENSUS TO OFFSET NAVGEM. THE CLOSE AGREEMENT BETWEEN THE
MAJORITY OF GUIDANCE LENDS HIGH CONFIDENCE IN THE JTWC TRACK
FORECAST. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, WITH ALL
MODELS DEPICTING A WEAKENING TREND AFTER TAU 24. SOME OF THE MODELS
DO HAVE 02A WEAKENING AT A SLIGHTLY SLOWER PACE, WITH WEAKENING TO
30 KTS NEAR TAU 72 VICE TAU 48. HOWEVER, THE QUICKLY WORSENING
ENVIRONMENT AROUND TAU 48 IS REASONING FOR THE SLIGHTLY QUICKER
DISSIPATION THAN CONSENSUS. THE JTWC INTENSITY FORECAST IS PLACED
WITH MEDIUM CONFIDENCE DUE TO THE VARIATIONS IN WEAKENING TRENDS.

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