Advisories

WDPN31 PGTW 062100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15E (NOLO) WARNING NR 065//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.3N 166.4E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 361 NM NORTH OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: WESTWARD AT 24 KTS
   SIGNIFICANT WAVE HEIGHT: 39 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
RAPIDLY DEGRADING TYPHOON. THE PREVIOUSLY CLEAR EYE RAPIDLY FILLED
AND COLLAPSED AROUND 061200Z IN RESPONSE TO THE ONSET OF STRONG
NORTHEASTERLY SHEAR, DIAGNOSED BY THE GFS AND ECMWF MODELS AT
AROUND 30 KT IN THE 850-300 MB LAYER. IT IS LIKELY THAT THE VORTEX
IS TILTED SOMEWHAT SOUTHWARD WITH HEIGHT DUE TO THE SHEAR, BUT NO
CURRENTLY AVAILABLE DATA MAKES THIS OBVIOUS. AGENCY DVORAK FIXES
AND AUTOMATED SATELLITE-BASED INTENSITY ESTIMATES HAVE
APPROPRIATELY CRATERED OVER THE PAST SIX HOURS, AS 15E IS LIKELY IN
THE THROWS OF A RAPID WEAKENING PHASE. THE INITIAL INTENSITY IS SET
AT 80 KT USING A BLEND OF AGENCY CI NUMBERS AND AUTOMATED
ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T5.0 - 90 KTS
   PHFO: T4.5 - 77 KTS
   CIMSS ADT: 77 KTS AT 061730Z
   CIMSS D-MINT: 79 KTS AT 061823Z
   CIMSS D-PRINT: 81 KTS AT 061800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TYPHOON NOLO (15E) IS ACCELERATING WESTWARD
UNDER THE INFLUENCE OF A STRENGTHENING RIDGE TO THE NORTH. A RAPID
WEAKENING PHASE APPEARS TO BE IN PROGRESS IN RESPONSE TO A STEP
CHANGE INCREASE IN VERTICAL SHEAR ASSOCIATED WITH THE NORTHEASTERLY
FLOW ALOFT AROUND THIS RIDGE, ENHANCED BY OUTFLOW FROM TY 26W EAST
OF JAPAN. DYNAMICAL AND AI-BASED MODEL GUIDANCE IS IN GOOD
AGREEMENT ON SIGNIFICANT WEAKENING IN THE SHORT TERM, LIKELY TO
BELOW TYPHOON STRENGTH IN 24 HOURS. IN ABOUT 48 HOURS, 15E IS
FORECAST TO BEGIN ROUNDING THE WESTERN PERIPHERY OF THE
AFOREMENTIONED STEERING RIDGE, WHERE SHEAR WILL SLACKEN FOR ABOUT A
DAY, POTENTIALLY ALLOWING NOLO TO REINTENSIFY SOMEWHAT. AFTER ABOUT
TAU 72, PROXIMITY TO THE MID-LATITUDE JET AND PROGRESSIVELY COOLING
SEA SURFACE TEMPERATURES ARE EXPECTED TO WEAKEN THE STORM THROUGH
THE END OF THE FORECAST PERIOD. THE TRACK FORECAST HAS MUCH HIGHER
THAN AVERAGE UNCERTAINTY DUE TO COMPOUNDING SOURCES OF SENSITIVITY.
FIRSTLY, TROPICAL STORM 27W IS CURRENTLY LESS THAN 650 NM SOUTH OF
15E AND WILL REMAIN AT LEAST THIS CLOSE OVER THE NEXT 2 TO 3 DAYS.
TS 27W WILL LIKELY HAVE A BINARY INTERACTION EFFECT ON 15E, THE
MAGNITUDE OF WHICH WILL DEPEND ON ITS OWN INTENISTY AND TRACK. IN
SOME MODELS, SUCH AS THE ECMWF, THE TWO STORMS BECOME ENTWINED IN A
WAY THAT SIGNIFICANTLY DELAYS 15E'S RECURVATURE INTO THE
MID-LATITUDE JET, ALSO DRAGGING 15E MUCH FARTHER WEST BEFORE
TURNING. IN OTHER MODELS, NOTABLY MOST OF THE AI-BASED GUIDANCE,
15E GAINS SEPARATION FROM 27W AND ESCAPES INTO THE MID-LATITUDES
MUCH EARLIER. THE SECOND SOURCE OF UNCERTAINTY STEMS FROM THE ZONAL
JET PATTERN THAT EMERGES AFTER THE LONGWAVE TROUGH CURRENTLY OVER
JAPAN LIFTS OUT AND LEAVES A FLATTENED JET NORTH OF 15E. THE OLD
COLD FRONT DANGLING BEHIND THE CURRENTLY RECURVING TY 26W WILL
LEAVE A WEAKNESS IN THE SUBTROPICAL RIDGE EAST OF JAPAN THAT IS
EXPECTED TO COAX 15E NORTHWESTWARD, EVENTUALLY LEADING TO CAPTURE
BY THE MID-LATITUDE WESTERLIES. DURING THIS PROCESS, THE STRONG
ZONAL JET WILL CREATE A TIGHT GRADIENT IN STEERING FLOW, MAKING
15E'S RECURVING TRACK HIGHLY SENSITIVE TO ITS EXACT STARTING
POSITION IN 2 TO 3 DAYS, WHICH ITSELF HAS UNCERTAINTY AS
AFOREMENTIONED. PHYSICS-BASED AND AI-BASED MODEL GUIDANCE IS HIGHLY
SPREAD, WITH ENVELOPE WIDTH OVER 800 NM AT TAU 120.THE JTWC TRACK
FORECAST IS THUS PLACED WITH LOWER THAN AVERAGE CONFIDENCE
THROUGHOUT THE FORECAST PERIOD.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS PLACED NEAR A BLEND OF
THE PHYSICS-BASED MODEL CONSENSUS AND AI-BASED MODEL CONSENSUS, AND
IS MOST SIMILAR TO THE GFS AND GOOGLE DEEPMIND ENSEMBLE MEAN,
THOUGH SLOWER THAN BOTH. THE JTWC INTENSITY FORECAST IS 5 TO 10 KT
ABOVE THE MULTI-MODEL CONSENSUS FOR THE FIRST 72 HOURS, AND LOWER
THAN THE PREVIOUS FORECAST. THE INTENSITY AIDS AGREE MUCH BETTER
THAN THE TRACK AIDS, THOUGH RECURVATURE TIMING AND THE NATURE OF
15E'S INTERACTION WITH 27W DO ADD MODERATE UNCERTAINTY TO THE
INTENSITY PROJECTION.

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