WDPN33 PGTW 041500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W (HAIYAN) WARNING NR 
06//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 31W (HAIYAN), LOCATED APPROXIMATELY 640 NM EAST-
SOUTHEAST OF YAP, HAS TRACKED WESTWARD AT 19 KNOTS OVER THE PAST SIX 
HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) DEPICTS AN 
EXPANSIVE SYSTEM THAT IS STEADILY CONSOLIDATING. THE LOW-LEVEL 
CIRCULATION CENTER (LLCC) IS BETTER DEFINED AND CENTRAL CONVECTION 
HAS DEEPENED WITH FORMATIVE BANDS WRAPPING TIGHTER INTO THE LLCC. A 
041043Z TRMM MICROWAVE IMAGE REVEALS THE EXTENT OF THE FRAGMENTED, 
THOUGH IMPROVING, BANDING FEATURES SURROUNDING THE ENTIRETY OF THE 
SYSTEM. THE INITIAL POSITION IS BASED ON THE EIR ANIMATION AND THE 
CUSP FEATURE IN THE AFOREMENTIONED TRMM IMAGE WITH GOOD CONFIDENCE. 
THE INITIAL INTENSITY OF 45 KNOTS IS BASED ON THE HIGH END OF DVORAK 
ESTIMATES FROM PGTW, RJTD, AND KNES RANGING FROM 35-45 KNOTS. UPPER 
LEVEL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH WEAK TO 
MODERATE (05 TO 15 KNOT) VERTICAL WIND SHEAR (VWS) THAT IS EASILY 
BEING OFFSET BY GOOD RADIAL OUTFLOW, AS EVIDENT ON ANIMATED WATER 
VAPOR IMAGERY. TS 31W IS CURRENTLY TRACKING ALONG THE SOUTHERN 
PERIPHERY OF THE DEEP-LAYERED STEERING SUBTROPICAL RIDGE (STR) TO 
THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM 
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 31W IS EXPECTED TO MAINTAIN A WEST-NORTHWEST TRACK ALONG 
THE SOUTHERN EDGE OF THE STR. GRADUAL INTENSIFICATION THAT IS HIGHER 
THAN NUMERIC GUIDANCE IS FORECAST AS FAVORABLE UPPER LEVEL 
CONDITIONS, IN ADDITION TO PERENNIALLY WARM SEA SURFACE 
TEMPERATURES, PREVAIL. TS 31W IS FORECAST TO REACH TYPHOON STRENGTH 
BY TAU 24 AS IT APPROACHES THE ISLAND OF YAP. BY TAU 72, TS 31W WILL 
BE AN INTENSE TYPHOON AT 120 KNOTS NORTHWEST OF PALAU.
   C. IN THE EXTENDED TAUS, TS HAIYAN WILL CONTINUE TRACKING THROUGH 
THE PHILIPPINE SEA WHERE INCREASINGLY FAVORABLE UPPER LEVEL AND SEA 
SURFACE CONDITIONS MAY LEAD TO RAPID INTENSIFICATION AND REACHING 
PEAK INTENSITY SOMETIME BEFORE LANDFALL WITH THE ISLAND OF SAMAR, 
PHILIPPINES. THE SYSTEM WILL SLIGHTLY ERODE AS IT TRACKS OVER THE 
PHILIPPINES THROUGH TAU 96, EVENTUALLY EMERGING IN THE SOUTH CHINA 
SEA AT AN INTENSITY OF 105 KNOTS NEAR TAU 120. DYNAMIC MODEL 
GUIDANCE IS IN GENERALLY TIGHT AGREEMENT THROUGHOUT THE FORECAST 
PERIOD, THUS, THE JTWC FORECAST TRACK IS LAID CLOSE TO THE MULTI-
MODEL CONSENSUS. THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST DUE 
TO THE GOOD AGREEMENT AMONGST OBJECTIVE AIDS AND THE WELL-
ESTABLISHED STEERING MECHANISM.//
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