Advisories

WDPN31 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (KROVANH) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.0N 133.4E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 408 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: EASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A POORLY
ORGANIZED, BROAD CIRCULATION LACKING PERSISTENT CENTRAL CONVECTION.
THE EIR ALSO DEPICTS SOME DRY AIR ENTRAINMENT FROM THE WEST WORKING
ITS WAY INTO THE SYSTEM CENTER. THE LOW-LEVEL CIRCULATION CENTER IS
SOMEWHAT AMBIGUOUS DUE TO THE DISORGANIZED NATURE OF THE SYSTEM AND
APPARENT ELONGATION ALONG A GENERALLY NORTHWEST-SOUTHEAST AXIS.
FURTHER ANALYSIS OF THE VORTEX STRUCTURE HAS BEEN PREVENTED BY A
LACK OF RECENT SCATTEROMETER OR MICROWAVE IMAGERY. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
AFOREMENTIONED AMBIGUITY OF THE LLCC STRUCTURE, BASED ON LOW-LEVEL
CLOUD TRACING IN THE ANIMATED EIR. THE INITIAL INTENSITY OF 35 KTS
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES
AND AN EARLIER 011430Z PARTIAL SCATTEROMETER PASS THAT DEPICTED 35
KT WINDS IN THE SOUTHWEST QUADRANT. THE ENVIRONMENT IS
CHARACTERIZED AS MARGINALLY FAVORABLE, WITH MODERATE EQUATORWARD
OUTFLOW ALOFT, LOW (10-15 KTS) VERTICAL WIND SHEAR, SUBSIDENCE OVER
THE WESTERN PERIPHERY, AND WARM (28-29 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT WITH A
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST AND A NEAR
EQUATORIAL RIDGE (NER) TO THE SOUTHWEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RCTP: T2.5 - 35 KTS
   CIMSS ADT: 33 KTS AT 011740Z
   CIMSS AIDT: 36 KTS AT 011740Z
   CIMSS D-MINT: 30 KTS AT 011622Z
   CIMSS D-PRINT: 27 KTS AT 011740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE WEST

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 22W IS FORECAST TO
CONTINUE TRACKING SLOWLY OVER THE NEXT 6-12 HOURS WITHIN THE
COMPETING AND WEAK STEERING ENVIRONMENT. THE NER TO THE SOUTHWEST
IS EXPECTED TO WEAKEN AND SHIFT WESTWARD DURING THAT TIME AND ALLOW
THE STR TO THE NORTHEAST BECOME THE PRIMARY STEERING INFLUENCE.
THE FORECAST TRACK UNDER THIS STEERING ENVIRONMENT IS
NORTHWESTWARD THROUGH TAU 48 AS 22W APPROACHES THE RYUKYU ISLANDS.
AFTER TAU 48, A MIDLATITUDE TROUGH IS EXPECTED TO WEAKEN THE
STEERING RIDGE AND LEAVE THE SYSTEM IN A WEAK STEERING ENVIRONMENT.
IN GENERAL, THE SYSTEM IS EXPECTED TO REMAIN QUASI-STATIONARY
BETWEEN TAU 48-72, TURNING SLOWLY POLEWARD THEN SOUTHEASTWARD AS
THE TROUGH EXITS TO THE EAST AND THE STR IS ALLOWED TO BUILD BACK
INTO THE AREA. IN TERMS OF INTENSITY, THE SYSTEM IS EXPECTED TO
CONTINUE SLOWLY CONSOLIDATING OVER THE NEXT 24 HOURS, THEN
GRADUALLY INTENSIFY TO A PEAK AROUND 45 KTS THROUGH TAU 72. A SLOW
WEAKENING TREND IS EXPECTED THROUGH THE REMAINDER OF THE FORECAST
PERIOD.

MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN VERY POOR
AGREEMENT THROUGHOUT THE ENTIRE FORECAST PERIOD. THERE IS SOME
CONSENSUS AMONG THE GUIDANCE SUITE REGARDING A GENERALLY
NORTHWESTWARD TRACK IN THE FIRST 49 HOURS, BUT THERE REMAINS A
SIZEABLE CROSS-TRACK AND ALONG-TRACK SPREAD. THERE IS VIRTUALLY NO
CONSENSUS ABOUT THE AFTER TAU 48, WITH ALL TRACK GUIDANCE DIVERGING
WITHIN THE WEAK STEERING ENVIRONMENT. EVENTUALLY, MOST MODELS TAKE
AN EASTWARD OR SOUTHEASTWARD TRACK AWAY FROM THE RYUKUS, BUT THE
JTWC TRACK IS PLACED WITH LOW CONFIDENCE THROUGHOUT THE FORECAST
PERIOD. INTENSITY GUIDANCE GENERALLY AGREES ABOUT THE GRADUAL
INCREASE IN INTENSITY FOLLOWED BY GRADUAL WEAKENING, HOWEVER, THE
RATE OF CONSOLIDATION IN THE NEAR TERM AND UNCERTAINTY ABOUT THE
TRACK IN THE LONGER TERM STILL LEND LOW CONFIDENCE TO THE JTWC
INTENSITY FORECAST. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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