WDPN31 PGTW 130300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W WARNING NR 01//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL DEPRESSION (TD) 15W (FIFTEEN), LOCATED APPROXIMATELY 
260 NM WEST-SOUTHWEST OF GUAM, HAS TRACKED WEST-SOUTHWEST AT 07 
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY AND A 122231Z SSMIS MICROWAVE IMAGE SHOW IMPROVED CONVECTIVE 
BANDING WRAPPING INTO A LOW LEVEL CIRCULATION CENTER (LLCC). THE 
INITIAL POSITION IS BASED ON ITOP C-130 OBSERVATIONS AND THE 
AFOREMENTIONED SSMIS IMAGE. THE INITIAL INTENSITY IS BASED ON PGTW 
AND KNES DVORAK ESTIMATES RANGING FROM 25 TO 30 KNOTS. UPPER LEVEL 
ANALYSIS INDICATES THE LLCC IS LOCATED BENEATH THE SUBTROPICAL RIDGE 
AXIS IN AN AREA OF DIVERGENCE AND LOW VERTICAL WIND SHEAR, FAVORABLE 
FOR CONTINUED DEVELOPMENT. ADDITIONALLY, WATER VAPOR IMAGERY DEPICTS 
GOOD EQUATORWARD OUTFLOW AND ENHANCED POLEWARD OUTFLOW INTO A TUTT 
CELL LOCATED TO THE NORTHEAST. 
3. FORECAST REASONING.
   A. THIS IS THE FIRST ISSUANCE OF THE PROGNOSTIC REASONING MESSAGE.
   B. TD 15W IS CURRENTLY TRACKING ALONG THE SOUTHERN PERIPHERY OF A 
LOW- TO MID- LEVEL STEERING RIDGE AND IS FORECAST TO CONTINUE 
THROUGH TAU 36. AFTER TAU 36, AN UPPER LEVEL, MID-LATITUDE TROUGH IS 
EXPECTED TO WEAKEN THE STEERING RIDGE AND ALLOW THE SYSTEM TO TURN 
NORTHWESTWARD. TD 15W IS FORECAST TO STEADILY INTENSIFY THROUGH TAU 
48, AS POLEWARD OUTFLOW INCREASES INTO THE MID-LATITUDE TROUGH.
   C. AFTER TAU 72, TD 15W IS FORECAST TO CONTINUE TRACKING 
NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE STEERING 
RIDGE. POLEWARD OUTFLOW SHOULD CONTINUE TO ENHANCE INTO THE MID-
LATITUDE TROUGH AND ALLOW FOR FURTHER INTENSIFICATION. IN THE LATER 
TAUS, THE RIDGE IS EXPECTED TO RE-BUILD TO THE NORTH, FOLLOWING THE 
PASSING MID-LATITUDE TROUGH AND ALLOW TD 15W TO TURN MORE WESTWARD. 
NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT, HOWEVER, GFDN 
ERRONEOUSLY TURNS THE SYSTEM IMMEDIATELY NORTHWARD. THIS FORECAST IS 
IN GOOD AGREEMENT WITH THE GFS AND NOGAPS MODELS.//
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