Advisories

WDPN32 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (CHOI-WAN) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.9N 145.1E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 110 NM NORTH-NORTHWEST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 26W STRUGGLING TO CONSOLIDATE AS THE CENTRAL CONVECTION
OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS SOMEWHAT
DETERIORATED AND CLOUD TOPS HAVE WARMED FROM -75 C TO -60 C OVER
THE LAST SIX HOURS. PERIPHERAL CONVECTIVE BANDING REMAINS EXPANSIVE
AND BETTER DEFINED BUT PRIMARILY CONFINED TO THE SOUTHERN
SEMICIRCLE AS THE SYSTEM EXPERIENCES 15-20 KTS OF NORTHEASTERLY
VERTICAL WIND SHEAR (VWS). HOWEVER, ALL OTHER ENVIRONMENTAL FACTORS
REMAIN FAVORABLE WITH WARM (30-31 C) SEA SURFACE TEMPERATURES, HIGH
(140 KJ PER CM SQUARED) OCEAN HEAT CONTENT (OHC), AND MODERATE
EQUATORWARD OUTFLOW. THE INITIAL POSITION IS PLACED WITH LOW
CONFIDENCE BASED ON THE OBSCURED LLCC IN EIR, WITH SOUTHWESTERLY
SURFACE OBSERVATIONS FROM THE MARIANAS INDICATING THAT 26W IS NOW
TO THE WEST OF THE ISLAND CHAIN. THE INITIAL INTENSITY IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON CONSISTENT SURFACE OBSERVATIONS OF
SUSTAINED 30 KTS FROM SAIPAN OVER THE LAST FOUR HOURS AS WELL AS
THE AGENCY DVORAK AND CIMSS OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTWARD EXTENSION OF SUBTROPICAL RIDGE
CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS SATCON: 52 KTS AT 011615Z
   CIMSS ADT: 43 KTS AT 011740Z
   CIMSS AIDT: 38 KTS AT 011740Z
   CIMSS D-MINT: 57 KTS AT 011617Z
   CIMSS D-PRINT: 48 KTS AT 011710Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: TS 26W IS FORECAST TO CONTINUE TRACKING SLOWLY
WEST-NORTHWESTWARD OVER THE NEXT 6 TO 12 HOURS UNDER THE INFLUENCE
OF THE WESTERN EXTENSION OF THE SUBTROPICAL RIDGE (STR) CENTERED TO
THE NORTHEAST. AFTER THIS POINT, A SHORTWAVE TROUGH IS EXPECTED TO
PROPAGATE EASTWARD AND REORIENT THE STR, LEADING TO A POLEWARD
TURN. A BRIEF NORTH-NORTHEASTWARD TRACK IS EXPECTED DUE TO THE
INFLUENCE OF A NEAR-EQUATORIAL RIDGE (NER) CENTERED TO THE
SOUTHEAST. AT TAU 60, THE STR WILL REBUILD A SMALL WESTWARD
EXTENSION AND REGAIN PRIMARY STEERING INFLUENCE, CAUSING THE LATER
NORTH-NORTHWESTWARD THEN NORTHEASTWARD TURNS DEPICTED AT TAUS 96
AND 120. REGARDING INTENSITY, TS 26W IS FORECAST TO INTENSIFY TO A
PEAK OF 105 KTS AT TAU 60, ALTHOUGH A HIGHER PEAK COULD BE POSSIBLE
DEPENDING ON THE RATE OF CONSOLIDATION BY TS 26W. RAPID
INTENSIFICATION (RI) IS FORECAST TO OCCUR BETWEEN TAUS 24 AND 48 AS
THE SYSTEM CONTINUES TO CONSOLIDATE AND ENTERS A REGION OF LOWER
VWS, IMPROVED OUTFLOW ALOFT, AND CONTINUED FAVORABLE OHC VALUES.
AFTER TAU 60, TS 26W IS FORECAST TO BEGIN A GENERAL WEAKENING TREND
AS OHC VALUES LOWER TO BELOW 100 KJ PER CM SQUARED.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE
OVERALL POLEWARD, WINDING SHAPE OF THE TRACK FOR THE REMAINDER OF
THE FORECAST PERIOD. HOWEVER, PHYSICS AND AI BASED MODELS DIVERGE
ON TRACK SPEED AND THUS THE LOCATION OF THE WESTWARD AND EASTWARD
TURNS BY TAU 96, LEADING TO AN ALONG TRACK SPREAD OF 390 NM AND
CROSS TRACK SPREAD OF 240 NM BY TAU 120, WITH AI MODELS MAKING UP
THE EASTERN AND FASTER PORTION OF THE GUIDANCE PACKAGE. THE
OFFICIAL JTWC FORECAST TRACK IS PLACED WITH HIGH CONFIDENCE OUT TO
TAU 72, IN GOOD AGREEMENT WITH THE MULTI-MODEL AND AI CONSENSUS AND
MEDIUM CONFIDENCE THEREAFTER, FOLLOWING THE FASTER TRACK SPEED AND
THUS MORE EASTWARD TRACK DEPICTED BY THE AI CONSENSUS AND GOOGLE
DEEPMIND. MODEL INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT ON A
STEADY TO RAPID INTENSIFICATION RATE, A PEAK BETWEEN TAUS 48 AND
72, AND A GENERAL WEAKENING TREND THEREAFTER. HOWEVER, INTENSITIES
RANGE FROM A PEAK OF 70 TO 120 KTS AT THE AREA OF LARGEST SPREAD AT
TAU 48. SEVERAL RI MODELS HAVE CONTINUED TO POPULATE, LENDING
CONFIDENCE TO THE PERIOD OF RI AT TAU 24, WITH SOME POSSIBILITY FOR
ONSET TO BEGIN SOONER IF ENVIRONMENTAL CONDITIONS AND STRUCTURE
IMPROVE EARLIER. THE OFFICIAL JTWC INTENSITY FORECAST IS ASSESSED
WITH MEDIUM CONFIDENCE FOR THE ENTIRETY OF THE FORECAST PERIOD, DUE
TO THE UNCERTAINTY WITH TIMING OF RI AND SUBSEQUENT PEAK INTENSITY
VALUE, PLACED JUST ABOVE THE MULTI-MODEL CONSENSUS. 

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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