Advisories

WDPN31 PGTW 030300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (DOLPHIN) WARNING NR 029//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.4N 148.4E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 388 NM EAST OF IWO TO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 52 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)
12W UNDERGOING SIGNIFICANT STRUCTURAL CHANGES. THE EYE HAS BECOME
MORE CLOUD-FILLED AND IS COOLING, WHILE THE SURROUNDING CLOUD TOPS
OF THE CENTRAL DENSE OVERCAST (CDO) HAVE WARMED. MEANWHILE,
MULTIPLE, VIGOROUS BANDS SPIRAL AROUND THE CDO. THE DETERIORATION
IS THE RESULT OF THE ANTICIPATED EYEWALL REPLACEMENT CYCLE (ERC). A
021831Z SSMIS 37 GHZ IMAGE CONFIRMS THAT THE ERC HAS BEGUN IN
EARNEST, CLEARLY SHOWING A LOWER-LEVEL RING COMPLETELY SURROUNDING
THE INNER EYEWALL. A 022327Z ASCAT-C PASS REVEALS THAT THE
STORM-FORCE WIND RADII HAVE CONTRACTED SLIGHTLY, WHILE THE
GALE-FORCE EXTENT HAS EXPANDED. THE WIND FIELD IS ALSO QUITE
ASYMMETRIC, WITH MUCH LARGER WIND RADII OBSERVED IN THE NORTHERN
SEMICIRCLE. THE SURROUNDING ENVIRONMENT REMAINS FAVORABLE,
CHARACTERIZED BY VERY WARM SEA SURFACE TEMPERATURES (SST) AND LOW
VERTICAL WIND SHEAR (VWS), OFFSET BY LOWER OCEAN HEAT CONTENT
(OHC). THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE EYE FEATURE IN THE MSI. DUE TO THE CONTINUED DEGRADATION OF
THE INNER CORE, THE INITIAL INTENSITY HAS BEEN LOWERED TO 100 KTS,
WHICH IS SUPPORTED BY THE MAJORITY OF T5.5 AGENCY DVORAK FIXES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: THE SOUTHWESTWARD EXTENSION OF THE
DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED FAR TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 113 KTS AT 021500Z
   CIMSS ADT: 102 KTS AT 030000Z
   CIMSS AIDT: 100 KTS AT 030000Z
   CIMSS D-MINT: 108 KTS AT 021918Z
   CIMSS D-PRINT: 104 KTS AT 030000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 12W WILL MAINTAIN A WEST-NORTHWESTWARD
TRAJECTORY, STEERED ALONG THE SOUTHWESTERN PERIPHERY OF A STR
CENTERED NEAR 42N 176W. BY TAU 36, A SEPARATE RIDGE OVER THE KOREAN
PENINSULA WILL CAPTURE THE SYSTEM AND DRIVE IT IN A SIMILAR
DIRECTION OF MOTION. AS THE SYSTEM TRACKS TOWARD THE RYUKYU
ISLANDS, A TROUGH PASSING THROUGH EASTERN SIBERIA WILL FLATTEN THE
STEERING RIDGE, RESULTING IN A WEAKER STEERING GRADIENT.
CONSEQUENTLY, THE FORWARD MOTION OF TY 12W WILL SLOW FROM 12 KTS AT
TAU 36 TO 08 KTS BY TAU 120. THE COMBINATION OF LOWER OHC AND THE
ERC HAS SIGNIFICANTLY WEAKENED THE SYSTEM BY 25 KTS OVER THE PAST
24 HOURS. CONTINUED WEAKENING TO AROUND 85 KTS WILL OCCUR DUE TO
THE ONGOING ERC. AN ADDITIONAL COMPLICATING FACTOR WILL EMERGE
BETWEEN TAU 12 AND TAU 36, AS THE SYSTEM ENCOUNTERS A BRIEF PERIOD
OF LOW TO MODERATE NORTHERLY VWS OF 15-20 KT, INDUCED BY AN
UPPER-LEVEL RIDGE OVER THE SEA OF JAPAN. IT IS POSSIBLE THAT THIS
SHEAR COULD DISRUPT AND PROLONG THE ERC, POTENTIALLY CAUSING MORE
WEAKENING THAN CURRENTLY FORECAST. BEYOND TAU 36, TY 12W WILL
TRAVERSE VERY WARM SST OF 30-31 DEGREES CELSIUS IN A LOWER-SHEAR
ENVIRONMENT. HOWEVER, THE PERSISTENTLY LOW OHC ALONG THE FORECAST
TRACK WILL LIMIT INTENSIFICATION. THEREFORE, THE FORECAST CALLS FOR
THE INTENSITY OF TY 12W TO REMAIN GENERALLY STEADY-STATE THROUGH
TAU 120. THE ONGOING ERC WILL CAUSE THE WIND FIELD TO FURTHER
EXPAND, ENSURING THAT HAZARDS WILL EXTEND FAR FROM THE STORM
CENTER.

MODEL DISCUSSION: THE MODEL TRACKERS ARE TIGHTLY GROUPED THROUGH
THE ENTIRE FORECAST PERIOD, ALL DEPICTING A WEST-NORTHWESTWARD
MOTION. THE SIGNIFICANT FORECAST CHALLENGE LIES IN THE STORM'S
FORWARD SPEED IN THE EXTENDED PERIOD. THE ALONG-TRACK SPREAD
INCREASES SIGNIFICANTLY FROM 170 NM AT TAU 96 TO 260 NM BY TAU 120.
THIS DIVERGENCE IN TIMING ARISES FROM MODEL SOLUTIONS THAT DIFFER
IN HOW THE RIDGE OVER THE KOREAN PENINSULA EVOLVES. THE FASTER
MODELS, WHICH INCLUDE ECMWF AND NAVGEM, KEEP A STRONGER RIDGE IN
PLACE, WHILE THE SLOWER SOLUTIONS OF GFS AND THE EXPERIMENTAL
GOOGLE DEEPMIND ERODE THE RIDGE TO A GREATER EXTENT. THE JTWC
FORECAST TRACK IS SET WITH HIGH CONFIDENCE NEAR THE MULTI-MODEL
CONSENSUS. AT TAU 96 AND TAU 120, THE FORECAST POINTS LIE NEARLY
HALFWAY BETWEEN THE FASTER ECMWF AND THE SLOWER GFS SOLUTIONS.
SIGNIFICANT SPREAD EXISTS AMONG THE INTENSITY AIDS. COAMPS-TC, THE
LONE OUTLIER THAT INTENSIFIES TY 12W TO 130 KTS, IS DISCOUNTED. THE
JTWC INTENSITY FORECAST IS MOST CLOSELY ALIGNED WITH THE HAFS-A
MODEL THROUGH TAU 36, SHOWING STEADY WEAKENING TO ACCOUNT FOR THE
ONGOING ERC AND A TEMPORARY INCREASE IN VWS. THEREAFTER, THE
FORECAST TRENDS CLOSER TO THE DEEPMIND SOLUTION. HAFS-A NOTABLY
PREDICTS SIGNIFICANT RE-INTENSIFICATION BEGINNING AT TAU 96, WITH
THE SYSTEM REACHING OVER 100 KTS BY TAU 120. THIS SOLUTION SUGGESTS
THE POTENTIAL FOR THE VERY LARGE EYEWALL TO ERODE AND A NEW,
SMALLER INNER CORE TO QUICKLY CONSOLIDATE. FOR NOW, THE FORECAST
KEEPS THE INTENSITY UNCHANGED IN THE EXTENDED PERIOD.

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