WDPN31 PGTW 182100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 07W (SEVEN) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.2N 145.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 91 NM SOUTH OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CONSOLIDATING, COMPACT CIRCULATION WITH SUSTAINED DEEP CONVECTION
OVER THE LOW LEVEL CIRCULATION CENTER (LLCC), A MARKED IMPROVEMENT
OVER THE PAST 18 HOURS. THE LLCC IS ELONGATED AND ASYMMETRIC, WITH
THE HIGHEST WINDS CLIPPING THE SOUTHERN MARIANA ISLANDS AND VERY
WEAK WESTERLIES IN THE SOUTHERN SEMICIRCLE. 07W EXHIBITS MODERATE
RADIAL OUTFLOW AND IS IN A HIGHLY CONDUCIVE ENVIRONMENT FOR
DEVELOPMENT CHARACTERIZED BY LOW VERTICAL WIND SHEAR (VWS), STRONG
DIVERGENCE ALOFT, VERY HIGH SEA SURFACE TEMPERATURES (SST) AND
OCEAN HEAT CONTENT (OHC), AND MODERATE DEEP LAYER MOISTURE OBSERVED
IN THE 181200Z GUAM SOUNDING FROM NWS TIYAN. AN 181430Z OSCAT-3
IMAGE DEPICTED 25-30 KTS WITHIN THE NORTHERN PERIPHERY OF THE LLCC.
THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
THE PGUA RADAR AND ALIGNS WITH THE DEVELOPING MID-LEVEL ROTATION
FROM THE HIMAWARI-9 SHORTWAVE IR IMAGERY. THE INITIAL INTENSITY IS
ASSESSED WITH HIGH CONFIDENCE BASED ON SUSTAINED WINDS NEARING 30
KTS AT GUAM INTERNATIONAL AIRPORT AND ANDERSEN AFB, WHICH IS
CONSISTENT WITH THE OSCAT-3 DATA BUT HIGHER THAN THE SUBJECTIVE
AGENCY FIXES AND OBJECTIVE ESTIMATES FROM CIMSS LISTED BELOW.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: WESTERN EXTENSION OF A LOW-MID LEVEL
SUBTROPICAL RIDGE (STR) CENTERED OVER MIDWAY ATOLL

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS
   KNES: T1.0 - 25 KTS
   CIMSS D-MINT: 17 KTS AT 181510Z
   CIMSS D-PRINT: 17 KTS AT 181800Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: 07W IS BEING STEERED WESTWARD BY AN EXTENSION
OF THE LOW- TO MID-LEVEL STR. THE SYSTEM WILL GAIN LATITUDE ON A
SUSTAINED WEST-NORTHWESTWARD TRAJECTORY AS IT DEEPENS AND BECOMES
DRIVEN BY THE DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE NORTH. AT
THE END OF THE FORECAST PERIOD, A STRONG RIDGE WILL BUILD OVER THE
SOUTH CHINA SEA. WHEN 07W ENCOUNTERS THIS RIDGE, IT WILL SLOW DOWN
AND TURN POLEWARD INTO A WEAKNESS OF THE STR. THE ENVIRONMENT WILL
BE HIGHLY FAVORABLE FOR INTENSIFICATION FOR THE FIRST 72-96 HOURS.
THE COMPACT SYSTEM WILL TRAVERSE OVER VERY WARM WATERS OF 30-31
DEGREE CELSIUS WITH LOW VWS. INITIALLY, THE FORECAST CALLS FOR SLOW
TO STEADY DEVELOPMENT DUE TO THE DISORGANIZED STRUCTURE OF THE
CIRCULATION. AT TAU 36, THE COMPACT INNER CORE SHOULD BECOME
WELL-FORMED, ALLOWING FOR 07W TO INTENSIFY VERY RAPIDLY. IN FACT,
THE SYSTEM IS PREDICTED TO INTENSIFY AT A RATE OF 50 KTS IN 24
HOURS, REACHING A PEAK OF AT LEAST 120 KTS AT TAU 96. IT IS QUITE
POSSIBLE THAT 07W COULD INTENSIFY FASTER AND PEAK HIGHER THAN
DEPICTED BY THE FORECAST. AT THE END OF THE PERIOD, THE SLOWER
TRACK SPEED WILL INDUCE UPWELLING OF COOLER SUB-SURFACE WATERS AND
CAUSE 07W TO WEAKEN.

MODEL DISCUSSION: THE RELIABLE MODEL GUIDANCE SUPPORTS A GENERAL
WEST-NORTHWEST TRACK THROUGH TAU 96 WITH SIGNIFICANT CROSS- AND
ALONG-TRACK SPREAD AT TAU 120. THE GEFS ENSEMBLE MEAN, GFS, AND
HAFS-A MODELS LIE ON THE POLEWARD SIDE OF THE GUIDANCE ENVELOPE,
WHILE ECMWF AND THE AI MODELS LIE ON THE OTHER END. THE FORECAST
TRACK IS PLACED VERY NEAR THE MULTI-MODEL CONSENSUS WITH A SLIGHT
NUDGE TOWARDS THE AI MODELS. THE CROSS-TRACK SPREAD INCREASES TO
350 NM AT TAU 120, DEMONSTRATING SUBSTANTIAL UNCERTAINTY IN THE
TIMING OF THE NORTHWARD SHIFT IN TRACK AT THE END OF THE FORECAST
PERIOD. THE INTENSITY GUIDANCE AGREES ON A SLOW TO GRADUAL RATE OF
DEVELOPMENT FOR THE FIRST 36 HOURS, FOLLOWED BY RAPID TO EXTREMELY
RAPID INTENSIFICATION FROM TAU 48 TO TAU 72. HAFS-A AND COAMPS-TC
ARE THE MOST AGGRESSIVE MODELS WITH A PEAK AT 135 KTS. THE CIMSS
AI-RI ALGORITHM ESTIMATES A 60 PERCENT CHANCE OF A 65 KT INCREASE
IN 72 HOURS. THE GFS MODEL IS MUCH WEAKER, TOPPING OUT AT 90 KTS.
THE INTENSITY FORECAST FOLLOWS THE CONSENSUS THROUGH TAU 48. FROM
TAU 60 TO TAU 96, THE FORECAST IS CLOSEST WITH THE MORE AGGRESSIVE
MODELS BUT HOLDS SHORT OF THE 135 KTS, WHICH IS NOT OUT OF THE
QUESTION IF THE CIRCULATION CAN QUICKLY AXISYMMETRIZE. THE FIRST
WARNING CALLS FOR A PEAK OF 120 KTS, WHICH IS CLOSEST TO THE
EXPERIMENTAL GOOGLE DEEPMIND MODEL, AND WEAKENS 07W TO THE MODEL
CONSENSUS OF 105 KTS AT TAU 120.

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