WDPN31 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 22W (GONI) WARNING
NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TYPHOON (TY) 22W (GONI), LOCATED APPROXIMATELY 106 NM
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT
11 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS SIGNIFICANTLY
ERODED AS IT DRAGGED ACROSS THE SOUTHEASTERN ISLANDS OF
LUZON. CENTRAL CONVECTIVE TOPS HAVE GREATLY WARMED AND
FEEDER BANDS HAVE BECOME FRAGMENTED. THE INITIAL POSITION
IS PLACED WITH FAIR CONFIDENCE BASED ON THE MSI AND COMPOSITE
RADAR LOOPS. THE INITIAL INTENSITY OF 75KTS IS DEDUCED FROM
NEARBY WIND AND MEAN SEA LEVEL PRESSURE OBSERVATIONS. UPPER
LEVEL DYNAMICS ARE MARGINAL WITH MODERATE (20-25KT) VERTICAL
WIND SHEAR (VWS) PARTIALLY OFFSET BY GOOD RADIAL OUTFLOW.
THE CYCLONE IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A
DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTHWEST.
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TY 22W WILL TRACK MORE WEST-NORTHWESTWARD JUST TO THE
SOUTH OF MANILA, AS THE STR RECEDES WESTWARD, AND EXIT INTO
THE SOUTH CHINA SEA (SCS) JUST BEFORE TAU 12. AFTER TAU 24,
THE STR WILL REBUILD AND DRIVE THE SYSTEM ON A WESTWARD TO
WEST-SOUTHWESTWARD TRAJECTORY. THE MARGINAL UPPER LEVEL
DYNAMICS COMBINED WITH FRICTIONAL EFFECTS FROM THE ISLANDS
WILL CONTINUE TO WEAKEN TY 22W TO 65KTS BY TAU 12. AFTERWARD,
THE ADDITION OF COOLING SEA SURFACE TEMPERATURES (SST) IN THE
SCS WILL AID IN WEAKENING THE SYSTEM TO 50KTS BY TAU 36.
AFTER TAU 36, THE ENVIRONMENT WILL BE IN A QUASI-EQUILIBRIUM AS
ROBUST RADIAL OUTFLOW IS OFFSET BY MODERATE VWS AND COOL SST,
SUSTAINING THE INTENSITY AT 50KTS UP TO TAU 72. NUMERICAL MODELS
ARE IN FAIRLY TIGHT AGREEMENT WITH GRADUAL, EVEN SPREADING TO
210NM AT TAU 72, LENDING HIGH CONFIDENCE IN THIS PORTION OF THE
JTWC TRACK FORECAST.
C. BEYOND TAU 72, TY GONI WILL CONTINUE WEST-SOUTHWESTWARD
UNDER THE SAME STR, MAKE LANDFALL OVER SOUTHERN VIETNAM NEAR
QUI NOHN SHORTLY AFTER TAU 96. COOLING SST AND LAND INTERACTION
WILL PRIMARILY ERODE THE SYSTEM TO 25KTS BY TAU 120. NUMERICAL
MODELS CONTINUE TO DIVERGE EVENLY TO OVER 500NM BY TAU 120. IN
VIEW OF THIS, THERE IS FAIR CONFIDENCE IN THE EXTENDED PORTION
OF THE JTWC TRACK FORECAST, WHICH IS LAID ALONG THE MULTI-
MODEL CONSENSUS.//
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