Tropical Storm SURIGAE Advisory mar, 20-04

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 02W (SURIGAE) WARNING NR 027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 02W (SURIGAE), LOCATED APPROXIMATELY 350 NM EAST OF
MANILA, PHILIPPINES, HAS TRACKED NORTHWARD AT 03 KTS OVER THE PAST
SIX HOURS. SURIGAE CONTINUES TO DISPLAY A LARGE CORE, WITH A 200140Z
GMI MICROWAVE PASS SHOWING AM INTENSE 65 NM DIAMETER PRIMARY
EYEWALL. A WEAKER INNER EYEWALL OF 30 NM DIAMETER REMAINS EVIDENT IN
MICROWAVE AND ENHANCED INFRARED (EIR) IMAGERY, THOUGH IT HAS SHOWN
SIGNS OF CONTINUED DEGRADATION IN RECENT HOURS AS THE CENTRAL WARM
SPOT IN EIR IMAGERY EXPANDS. THE CURRENT INTENSITY IS HELD CONSTANT
AT 115 KT, SUPPORTED BY DVORAK ESTIMATES OF T6.0 FROM RJTD AND
T6.0/6.5 FROM PGTW. SURIGAE?S ENVIRONMENT CONTINUES TO BE GENERALLY
FAVORABLE, WITH EXPANSIVE CIRRUS OUTFLOW REFLECTING THE LOW VERTICAL
WIND SHEAR (VWS) OF UNDER 10 KTS. BACKGROUND SEA SURFACE TEMPERATURE
(SST) REMAINS WARM, AROUND 28C, BUT COUPLED HWRF/HYCOM ANALYSIS
INDICATES THAT THE TYPHOON?S CIRCULATION IS AT LEAST PARTIALLY
OVERLAPPING A WAKE OF COOLED WATER ALONG THE STORM TRACK, INDUCED BY
SURIGAE?S SLOW FORWARD MOTION. THIS IS LIKELY THE PRIMARY INHIBITOR
CURRENTLY CAPPING SURIGAE?S INTENSITY.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY
SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. ABSENT ANY SIGNIFICANT ATMOSPHERIC INHIBITORS, THE PRIMARY
GOVERNORS OF INTENSITY DURING THE NEXT 48 HOURS ARE VORTEX STRUCTURE
AND UNDERLYING SST. THE HIGH-RESOLUTION HWRF MODEL IS CONSISTENTLY
PREDICTING SURIGAE?S LARGE CORE SIZE TO PERSIST AS MODERATE OCEAN
COOLING BENEATH THE TYPHOON RESISTS EYEWALL CONTRACTION. BOTH OF
THESE REALITIES FAVOR STEADY OR GRADUALLY DECREASING INTENSITY FOR
THE NEXT 48 HOURS UNTIL SURIGAE RECURVES NORTHEASTWARD, ENCOUNTERING
COOLER SST AND HIGHER VWS, AT WHICH POINT STEADY WEAKENING IS
EXPECTED. THE INTENSITY FORECAST IS IN BEST AGREEMENT WITH HWRF ON
THE HIGH SIDE OF THE MODEL CONSENSUS, PRIMARILY DUE TO THE
CONTINUING PERSISTENCE OF SURIGAE?S INTENSITY, DEFYING THE MORE
RAPID WEAKENING PREDICTED BY OTHER MODELS. COAMPS-TC IS 15-20 KTS
WEAKER THROUGH 48 HOURS, BUT SEEMINGLY DUE TO UNREALISTICALLY
EXTREME OCEAN COOLING IN THAT MODEL. THE TRACK FORECAST IS
ESSENTIALLY UNCHANGED FROM THE PREVIOUS ONE THROUGH 72 HOURS, WITH A
NORTHEASTWARD TURN EXPECTED IN ABOUT 48 HOURS, FOLLOWING THE
PERIPHERY OF AN UPPER-LEVEL RIDGE TO THE EAST OF THE TYPHOON AS A
MID-LATITUDE SHORTWAVE TROUGH APPROACHES FROM EASTERN CHINA. THIS
WILL INDUCE ACCELERATION IN FORWARD SPEED AS SURIGAE BEGINS
INTERACTING WITH THE SUBTROPICAL JET (STJ). CONFIDENCE IN THIS
PORTION OF THE FORECAST TRACK REMAINS HIGH.
   C. DURING THE 96-120 HOUR PERIOD, SURIGAE IS EXPECTED TO
ACCELERATE EAST-NORTHEASTWARD AS A SHORTWAVE TROUGH CROSSES THE
RYUKYU ISLANDS AND IMPARTS STRONG WESTERLY FLOW ON THE CYCLONE. MOST
MODELS CURRENTLY ANTICIPATE THAT THE TYPHOON WILL NOT PHASE
FAVORABLY WITH THIS SHORTWAVE, AND WILL LAG BEHIND AS THE SHORTWAVE
CONTINUES EASTWARD. THUS, HIGH VWS AND COOLING SST ARE EXPECTED TO
CAUSE STEADY WEAKENING THROUGH 120 HOURS TO BELOW TYPHOON INTENSITY.
SURIGAE WILL BE INTERACTING WITH A PRONOUNCED LOW-LEVEL THERMAL
GRADIENT DURING THIS TIME, WHICH IS EXPECTED TO INDUCE THE ONSET OF
EXTRATROPICAL TRANSITION AS THE CYCLONE ACQUIRES FRONTAL STRUCTURE.
THIS COMPLEX EVOLUTION INTRODUCES UNCERTAINTY IN EXACTLY HOW QUICKLY
THE CYCLONE WILL WEAKEN, AS WELL AS HOW SWIFTLY IT WILL MOVE
EASTWARD. THE TRACK FORECAST HAS BEEN NUDGED SLIGHTLY SOUTHWARD FROM
THE PREVIOUS ONE AT 96-120 HOURS ALONG WITH THE MULTI-MODEL
CONSENSUS TREND, AND IS OF MODERATE CONFIDENCE.//
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