Advisories

WDPN31 PGTW 252100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.4N 163.9E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 364 NM NORTHWEST OF KWAJALEIN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)
30W AS A DEVELOPING SYSTEM, THOUGH INTENSIFICATION BRIEFLY SLOWED
IN RESPONSE TO SLIGHTLY ELEVATED VERTICAL WIND SHEAR. THE UPPER
LEVEL CONVECTION IS BEGINNING TO WRAP ABOUT THE CENTER, SIGNALING
FURTHER INTENSIFICATION IS ONGOING. 30W IS POTENTIALLY IN THE MIDST
OF A BOUT OF RAPID INTENSIFICATION, THROUGH STRUCTURALLY, THE
PHYSICAL APPEARANCE LEAVES SOMETHING TO BE DESIRED. ENVIRONMENTAL
ANALYSIS REVEALS A FAVORABLE ENVIRONMENT, CHARACTERIZED BY LOW TO
MODERATE (15-20 KTS) VERTICAL WIND SHEAR (VWS), WARM (29-30 C) SEA
SURFACE TEMPERATURES (SST), MODERATE (75-10 KJ PER CM SQUARED)
OCEAN HEAT CONTENT (OHC), STRONG POLEWARD OUTFLOW. THE INITIAL
POSITION IS PLACED WITH LOW CONFIDENCE BASED ON THE AGENCY POSITION
FIXES. THE INITIAL INTENSITY OF 80 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE AGENCY DVORAK FIXES, SUPPLEMENTED BY THE
EARLIER 250718Z SAR DATA AND THE CIMSS AUTOMATED INTENSITY
ESTIMATES LISTED BELOW, THOUGH THE CIMSS ESTIMATES ARE ASSESSED TO
BE UNDERESTIMATING INTENSITY.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHWESTERN FLANK OF A DEEP-LAYER
NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.5 - 55 KTS
   PHFO: T4.5 - 77 KTS
   CIMSS SATCON: 64 KTS AT 251600Z
   CIMSS ADT: 59 KTS AT 251900Z
   CIMSS AIDT: 54 KTS AT 251900Z
   CIMSS D-MINT: 68 KTS AT 251704Z
   CIMSS D-PRINT: 65 KTS AT 251900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MILD MID-LEVEL DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: TS 30W (IN-FA) IS FORECAST TO CONTINUE TRACKING 
FOR THE NEXT 12 HOURS WHILE IT REMAINS ON THE NORTHWESTERN PERIPHERY 
OF THE NER CENTERED TO ITS SOUTHEAST. BY AROUND TAU 12, A SUBTROPICAL 
RIDGE (STR) TO THE NORTHWEST IS EXPECTED TO STRETCH TO THE EAST, 
CAUSING A COMPETING STEERING ENVIRONMENT BETWEEN TAU 12-36. THE STR IS 
EXPECTED TO GAIN STEERING AUTHORITY BY TAU 36, AND CAUSE 30W TO 
ACCELERATE WEST-NORTHWESTWARD THROUGH THE REMAINDER OF THE FORECAST 
PERIOD. BETWEEN TAU 48-60, AN UPPER-LEVEL TROUGH IS EXPECTED TO PASS 
NORTH OF THE STR, FORCING THE RIDGE TO RETREAT EASTWARD AND INDUCING A 
NORTHWESTWARD TRACK FOR 30W BETWEEN TAU 96-120. REGARDING INTENSITY, 
30W IS FORECAST TO BEGIN A PERIOD OF RAPID INTENSIFICATION (RI) 
IMMEDIATELY. 30W IS EXPECTED TO RI THROUGH TAU 24, WHEN THE COMPETING 
STEERING ENVIRONMENT TEMPORARILY HALTS INTENSIFICATION AND THE 
PROBABILITY FOR ADVERSE IMPACTS OF UPWELLING INCREASES. ONCE 30W 
TRANSITIONS STEERING ENVIRONMENTS AND BEGINS TRACKING WEST-
NORTHWESTWARD, IT WILL ENTER A REGION OF ELEVATED (100-125 KJ PER CM 
SQUARED) OHC VALUES, SUPPORTING A SECOND ROUND OF INTENSIFICATION. AS 
30W GAINS INTENSITY, IT MAY UNDERGO AN EYEWALL REPLACEMENT CYCLE 
(ERC), WHICH WOULD INDUCE TEMPORARY WEAKENING AND EXPAND THE 
WIND FIELD. AT LEAST ONE ERC IS DEPICTED IN THE HAFS-A MODEL GUIDANCE 
BETWEEN TAU 48-60. 30W IS EXPECTED TO PEAK AT TAU 96.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN GOOD 
AGREEMENT THROUGH TAU 120, THOUGH THERE ARE TWO OUTLIERS (NAVGEM AND 
EXPERIMENTAL AIGEFS) THAT ARE POLEWARD AND EQUATORWARD OF THE BULK OF 
MODEL GUIDANCE, RESPECTIVELY. DISREGARDING THOSE MEMBERS, THE JTWC 
TRACK FORECAST LIES WITH THE BULK OF PHYSICS-BASED MODEL GUIDANCE AND 
EXPERIMENTAL AI MEMBERS WITH OVERALL HIGH CONFIDENCE. RELIABLE 
INTENSITY AIDS ARE IN MODERATE AGREEMENT THROUGH TAU 120. SEVERAL JTWC 
RI AIDS MEET CRITERIA, HEAVILY SIGNALING THE POSSIBILITY OF RI FOR THE 
NEXT 24 HOURS. UNCERTAINTY EMERGES REGARDING THE INTENSITY FOLLOWING 
RI AND THE INTENSITY AS 30W CHANGES STEERING INFLUENCES. FOLLOWING TAU 
60, ALL MODELS GENERALLY AGREE ON A PERIOD OF STEADY INTENSIFICATION 
THROUGH TAU 120. THE JTWC INTENSITY FORECAST IS ASSESSED WITH OVERALL 
MEDIUM CONFIDENCE AND IS IN GOOD AGREEMENT WITH COAMPS-TC AND GOOGLE 
DEEPMIND. 

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