WDPN31 PGTW 061500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (BOPHA) WARNING NR 
44//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 26W (BOPHA) LOCATED APPROXIMATELY 295 NM 
WEST-SOUTHWEST OF MANILA, PHILIPPINES HAS TRACKED NORTH-
NORTHWESTWARD AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED 
ENHANCED INFRARED (EIR) SATELLITE IMAGERY CONTINUES TO SHOW THE 
DEEP CENTRAL CONVECTION WEAKENING AROUND AN ELONGATING LOW LEVEL 
CIRCULATION CENTER. THE CURRENT POSITION IS BASED ON THE EIR AND A 
061157Z SSMIS 91GHZ MICROWAVE IMAGE WITH FAIR CONFIDENCE. THE 
CURRENT INTENSITY HAS BEEN ASSESSED AT 55 KNOTS BASED ON THE 
CONTINUED WEAKENING SEEN IN THE EIR AND DVORAK INTENSITY ESTIMATES 
CONTINUING TO FALL, NOW RANGING FROM 45 TO 65 KNOTS. UPPER-LEVEL 
ANALYSIS INDICATES TS 26W REMAINS IN A COL REGION BETWEEN THE 
SUBTROPICAL RIDGES (STR) CENTERED TO THE EAST AND WEST WITH 
MODERATE (10 TO 20 KNOTS) VERTICAL WIND SHEAR (VWS). OUTFLOW 
REMAINS LIMITED INTO THE WESTERLIES TO THE NORTH. TS 26W IS 
CURRENTLY STEERING ALONG THE SOUTHWESTERN PERIPHERY OF THE EASTERN 
LOBE OF THE STR.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 26W IS FORECAST TO SLOW DOWN AS THE SYSTEM TRACKS FURTHER 
INTO THE COL REGION BETWEEN THE TWO LOBES OF THE STR. LOW OCEAN 
HEAT CONTENT, COOL DRY AIR ASSOCIATED WITH A NORTHEAST MONSOON 
SURGE, AND INCREASING VWS WILL FURTHER WEAKEN THE SYSTEM FOR THE 
REST OF THE FORECAST PERIOD. DUE TO THIS WEAKENING TREND THE STORM 
WILL BEGIN TO BE STEERED BY THE LOW-LEVEL FLOW, MAKING A SLOW TURN 
TO THE SOUTHWEST AFTER TAU 48 AND TRACK ALONG WITH THE NORTHEAST 
MONSOON.
   C. AFTER TAU 72, TS 26W IS EXPECTED TO INTERACT WITH A STRONG 
NORTHEAST MONSOON SURGE AND REMAIN IN A VERY WEAK STEERING 
ENVIRONMENT UNDERNEATH THE UPPER LEVEL COL REGION. THE SYSTEM IS 
EXPECTED TO TRACK NEARLY QUASI-STATIONARY AND ERRATICALLY WITH A 
POSSIBLE LOOPING MOTION PRIOR TO DISSIPATION AT TAU 120. MODEL 
GUIDANCE PERSISTS WITH A WIDE VARIATION OF SOLUTIONS IN THE 
EXTENDED TAUS. ALL THE MODELS INDICATE A STEADY WEAKENING TREND, 
WHICH LEADS TO THE LOOPING TRACK AS THE STEERING INFLUENCE SWITCHES 
FROM A DEEP LAYER FLOW TO GETTING CAUGHT WITHIN THE LOW LEVEL FLOW. 
IT APPEARS THE LARGE VARIATION IN THE MODELS IS BASED ON THE TIMING 
OF THIS STEERING TRANSITION. THE OFFICIAL JTWC FORECAST CONTINUES 
TRACKING TS 26W SLOWLY NORTHWESTWARD, NEARLY QUASI-STATIONARY, AND 
WEAKEN AS THE LOW-LEVEL FLOW BECOMES THE DOMINANT STEERING 
INFLUENCE TURNING THE SYSTEM SLOWLY TO THE SOUTHWEST IN THE LATER 
TAUS. DUE TO THE LARGE SPREAD IN MODEL GUIDANCE, TRACK CONFIDENCE 
REMAINS LOW.//
NNNN