Super Typhoon Hagibis : eyewall replacement cycle

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WESTERN NORTH PACIFIC

STY HAGIBIS(20W)
As of 00:00 UTC Oct 08, 2019:
Location: 16.9°N 143.7°E
Maximum Winds: 135 kt ( 250km/h)
Gusts: 165 kt ( 305km/h)
Minimum Central Pressure: 921 mb
CATEGORY 4 US
WDPN31 PGTW 080300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 20W (HAGIBIS) WARNING NR
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 20W (HAGIBIS), LOCATED APPROXIMATELY 204 NM
NORTH-NORTHWEST OF ANDERSEN AFB, GUAM, HAS TRACKED WEST-
NORTHWESTWARD AT 13 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS SPIRAL CONVECTIVE
BANDS WRAPPING INTO A SYMMETRIC, 8 NM DIAMETER EYE SURROUNDED BY A
DEFINED EYEWALL, LEADING TO HIGH CONFIDENCE IN THE INITIAL POSITION.
BASED ON THE DVORAK CURRENT INTENSITY (CI) ESTIMATES OF T6.5/127 KTS
FROM PGTW/RJTD AND T7.0/140 KTS FROM RCTP, THE INITIAL INTENSITY IS
SET AT 135 KTS WITH GOOD CONFIDENCE. THE SYSTEM HAS BEEN UNDERGOING
AN EYEWALL REPLACEMENT CYCLE (ERC), WITH A SECONDARY EYEWALL CLEARLY
EVIDENT IN 071945Z SSMIS 91 GHZ MICROWAVE IMAGE. UPPER-LEVEL
ANALYSIS INDICATES THE CONTINUED PRESENCE OF STRONG RADIAL OUTFLOW,
ENHANCED TOWARDS THE EAST AND SOUTH. TO THE NORTH OF THE SYSTEM,
THERE IS AN AREA OF DRY AIR WITH HIGH VERTICAL WIND SHEAR (VWS),
INHIBITING STRONG DEVELOPMENT OF A POLEWARD OUTFLOW CHANNEL. STY 20W
REMAINS IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY LOW (05-10 KTS)
VWS AND WARM (29-31 CELSIUS) SEA SURFACE TEMPERATURES (SST). UPON
COMPLETION OF THE CURRENT ERC, THERE WILL BE A POSSIBILITY FOR A
BRIEF PERIOD OF RE-INTENSIFICATION. HOWEVER, CLOUD TOP TEMPERATURES
HAVE WARMED SLIGHTLY, AND THE DEEPEST CONVECTION HAS BECOME MORE
RAGGED WITH SOME COOLING OF THE EYE. ANY RE-INTENSIFICATION IN THE
NEAR TERM WILL BE GRADUAL. THE SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST REMAINS THE PRIMARY STEERING INFLUENCE AS STY 20W TRACKS
WEST-NORTHWESTWARD ALONG ITS SOUTHWESTERN PERIPHERY.
3. FORECAST REASONING.     
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE LAST PROGNOSTIC REASONING MESSAGE.
   B. THROUGH TAU 24, STY 20W WILL TRACK NORTHWESTWARD ALONG THE
SOUTHWESTERN PERIPHERY OF THE AFOREMENTIONED STR. AT TAU 24, THE
SYSTEM WILL SHIFT TO A MORE NORTH-NORTHWESTWARD TRACK, SLOWING
SLIGHTLY AS IT GAINS LATITUDE. THE ENVIRONMENT IS EXPECTED TO REMAIN
FAVORABLE THROUGH TAU 72 WITH LOW VWS, HIGH SST, AND GOOD UPPER-
LEVEL OUTFLOW. DURING THIS PERIOD, THE OFFICIAL INTENSITY FORECAST
IS SLIGHTLY MORE AGGRESSIVE THAN THE INTENSITY CONSENSUS GIVEN THE
LIKELIHOOD OF RE-INTENSIFICATION AS STY 20W TRAVERSES AN AREA OF
GREATER MAXIMUM POTENTIAL INTENSITY (MPI). AFTERWARDS, GRADUAL
WEAKENING IS EXPECTED AS THE OUTFLOW BEGINS TO BE DISRUPTED TO THE
NORTHWEST DUE TO INTERACTION WITH AN APPROACHING TROUGH. WITH THE
GFS AND GFS ENSEMBLE AS THE EASTERNMOST OUTLIER AND THE UKMET AS THE
WESTERNMOST OUTLIER, THE NUMERICAL MODELS ARE IN GOOD AGREEMENT
THROUGH TAU 72, LENDING GOOD CONFIDENCE TO THIS PORTION OF THE JTWC
TRACK FORECAST.
   C. IN THE EXTENDED PERIOD, A SHORTWAVE TROUGH OVER JAPAN IS
EXPECTED TO DEEPEN, ERODING THE STR AND ALLOWING STY 20W TO TURN
NORTHWARD AS IT ROUNDS THE STR AXIS. AROUND TAU 96, THE SYSTEM WILL
BEGIN TO RECURVE, TRACKING NORTHEASTWARD THROUGH THE REMAINDER OF
THE FORECAST PERIOD. THE SYSTEM WILL SLOWLY WEAKEN IN RESPONSE TO
INCREASED VWS ASSOCIATED WITH THE APPROACHING TROUGH, OFFSETTING THE
OTHERWISE FAVORABLE ENVIRONMENT. THE NUMERICAL MODELS HAVE A CROSS-
TRACK SPREAD OF 130 NM AT TAU 120. HOWEVER, THERE IS VARIATION IN
THE TIMING OF THE RECURVATURE, RESULTING IN UNCERTAINTIES WITH THE
FORWARD MOTION OF THE SYSTEM AND LOW CONFIDENCE IN THE EXTENDED JTWC
FORECAST.//
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