WDPN32 PGTW 280300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 30W (THIRTY) 
WARNING NR 01//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 30W (THIRTY), LOCATED APPROXIMATELY 531 NM 
SOUTHEAST OF ANDERSEN AFB, HAS TRACKED WESTWARD AT 18 KNOTS OVER THE 
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A 
PARTIALLY EXPOSED CONSOLIDATING LOW LEVEL CIRCULATION CENTER (LLCC) 
UNDER A BROAD PERSISTENT AREA OF CONVECTION THAT ALSO FEATURES AN 
EQUATORWARD OUTFLOW TAIL. THE INITIAL POSITION IS PLACED WITH FAIR 
CONFIDENCE BASED ON THE MSI LOOP AND A 272220Z AMSU 89GHZ IMAGE. THE 
INITIAL INTENSITY OF 25 KTS IS BASED ON THE PGTW DVORAK ESTIMATE OF 
T1.5 (25 KTS), AND IS BELOW THE KNES ESTIMATE OF T2.0 (30 KTS). 
ENVIRONMENTAL ANALYSIS REVEALS MOSTLY EASTERLY DIFFLUENCE ALOFT WITH 
A SMALL POINT SOURCE DEVELOPING OVER TOP OF THE SYSTEM. 30W IS 
LOCATED ON THE BORDER OF MODERATE TO STRONG (15-20 KTS) VERTICAL 
WIND SHEAR (VWS) WHICH HAS BEEN DELAYING CONSOLIDATION. SEA SURFACE 
TEMPERATURES REMAIN FAVORABLE, BETWEEN 28 AND 29 DEGREES CELSIUS. TD 
30W IS MOVING WESTWARD UNDER THE SUBTROPICAL RIDGE (STR) TO ITS 
NORTH.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST 
PHILOSOPHY.
   B. TD 30W WILL CONTINUE TO TRACK WEST-NORTHWESTWARD TO 
NORTHWESTWARD THROUGH TAU 72. A MIDLATITUDE TROUGH MOVING WEST TO 
EAST TOWARDS JAPAN IS CAUSING THE STR TO RE-ORIENT, ALLOWING FOR 
NORTHWEST MOTION ALONG THE SOUTHWESTERN PERIPHERY OF THE STR. 
NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE PREDICTED TRACK 
THROUGH TAU 48, ALTHOUGH ECMWF AND THE EC ENSEMBLE ARE NORTHERN 
OUTLIERS, TRACKING SLIGHTLY CLOSER TO GUAM. THE JTWC FORECAST TRACK 
IS HEDGED BETWEEN THE MULTI-MODEL CONSENSUS AND ECMWF TRACK. STILL, 
GIVEN THE TIGHT MODEL GROUPING, WITH A SPREAD OF 115 NM AT TAU 48, 
THERE IS HIGH CONFIDENCE IN THIS PORTION OF THE FORECAST TRACK UNTIL 
TAU 48. AFTER TAU 48, NAVGEM AND COAMPS-TC (NAVGEM) DIVERGE TO THE 
NORTH, INCREASING THE UNCERTAINTY IN THE FORECAST. TD 30W IS LOCATED 
IN AN AREA OF MODERATE SHEAR, WHICH IS HINDERING ITS RATE OF 
DEVELOPMENT. HOWEVER, THE DEVELOPING POINT SOURCE ALOFT MAY ENHANCE 
OUTFLOW AND SUPPORT DEEPENING CONVECTION AND A FASTER RATE OF 
INTENSIFICATION. TD 30W IS FORECAST TO GRADUALLY INTENSITY THROUGH 
TAU 72, REACHING 90 KTS BY TAU 72. HOWEVER, THERE IS SIGNIFICANT 
SPREAD IN THE INTENSITY GUIDANCE, WITH NAVGEM AND ECMWF MAINTAINING 
THE SYSTEM AS MORE BROAD AND WEAK UNTIL AFTER TAU 48, WHEN THEY 
DEPICT THE SYSTEM CONTRACTING AND INTENSIFYING. THE JTWC INTENSITY 
FORECAST IS INITIALLY HEDGED LOWER THAN THE MULTI-MODEL CONSENSUS 
BASED ON THE MARGINAL ENVIRONMENT. THEREFORE, THERE IS LOW 
CONFIDENCE IN THIS PORTION OF THE JTWC INTENSITY FORECAST. 
   C. AFTER TAU 72, TD 30W WILL CONTINUE TO TRACK TO THE NORTHWEST 
AND INTENSIFY, REACHING 115 KTS BY TAU 120. HOWEVER, AFTER TAU 72, 
MODELS DIVERGE FURTHER INTO A TRIFURCATION SCENARIO. ECMWF AND THE 
EC ENSEMBLE ARE THE SOUTHERN OUTLIERS AND PREDICT A WEST-
NORTHWESTWARD TRACK TOWARDS LUZON. NAVGEM AND COAMPS-TC (NAVGEM) ARE 
THE NORTHERN OUTLIERS SHOWING A SIGNIFICANT RECURVE AND NORTHWARD 
TRACK. OTHER MODELS, INCLUDING UKMET, HWRF, AND GALWEM, CONTINUE TO 
MOVE 30W TO THE NORTHWEST. GIVEN THE SIGNIFICANT SPREAD IN MODEL 
GUIDANCE AND SEVERAL SCENARIOS POSSIBLE AT THE END OF THE FORECAST 
PERIOD, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK IN LATER 
TAUS.//
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