Tropical Storm TRAMI Advisory Cu, 21.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 28W (TWENTYEIGHT), LOCATED APPROXIMATELY
13 NM EAST-NORTHEAST OF ANDERSEN AFB, HAS TRACKED NORTHWESTWARD AT
08 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY DEPICTS FLARING DEEP CONVECTION NEAR THE LOW LEVEL
CIRCULATION CENTER (LLCC) AND BANDING FEATURES STARTING TO DEVELOP,
ESPECIALLY TO THE SOUTHEAST OF THE LLCC. THE INITIAL POSITION IS
PLACED WITH GOOD CONFIDENCE BASED ON RADAR IMAGERY FROM GUAM AND IS
SUPPORTED BY OBSERVATIONS FROM THE SURROUNDING ISLANDS. THE INITIAL
INTENSITY IS BASED ON THE PGTW AND KNES DVORAK CURRENT INTENSITY
ESTIMATES OF T1.5 (25 KNOTS). ENVIRONMENTAL CONDITIONS FOR TD 28W
ARE GENERALLY FAVORABLE WITH GOOD EQUATORWARD AND POLEWARD OUTFLOW,
LOW TO MODERATE VERTICAL WIND SHEAR, AND WARM SSTS (28-29 CELSIUS).
TD 28W IS CURRENTLY TRACKING ALONG A SOUTHERN EXTENSION OF AN
OTHERWISE EAST-WEST ORIENTED SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. BY TAU 24, TD 28W IS FORECAST TO GRADUALLY TURN ONTO A
WESTWARD TRACK AS THE EAST-WEST ORIENTATION OF THE STR BECOMES THE
DOMINANT INFLUENCE ON THE TRACK. THE STR TO THE NORTH WILL MAINTAIN
A GENERALLY WESTWARD TRACK THROUGH TAU 72. DURING THIS PERIOD, THE
ENVIRONMENT REMAINS FAVORABLE AND TD 28W IS EXPECTED TO RAPIDLY
INTENSIFY TO 115 KTS BY TAU 72. THE INTENSITY FORECAST CLOSELY
FOLLOWS THE INTENSITY CONSENSUS, HOWEVER SPREAD IS QUITE LARGE AMONG
THE MEMBERS WITH CTCI (130 KTS) AND COTI (75 KTS) REPRESENTING THE
EXTREMES AT TAU 72. MODEL TRACK GUIDANCE HAS ABOUT 170 NM OF SPREAD
BY TAU 72, THEREFORE CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST
IS FAIR.
   C. AFTER TAU 72, AN APPROACHING MID-LATITUDE TROUGH IS EXPECTED
TO CREATE A WEAKNESS IN THE STR AND ALLOW TD 28W TO BEGIN ROTATING
POLEWARD AROUND THE RIDGE AXIS. THE INTENSITY IS EXPECTED TO
CONTINUE TO GRADUALLY INCREASE AS CONDITIONS REMAIN FAVORABLE.
HOWEVER, BY TAU 120 THE JTWC FORECAST INTENSITY IS PLACED ABOVE THE
INTENSITY GUIDANCE BASED ON THE EXPECTATION THAT THE MID-LATITUDE
TROUGH WILL BE JUST WEST OF THE TROPICAL CYCLONE AND AID POLEWARD
OUTFLOW. HOWEVER, IF THE TROUGH PASSES TO THE EAST SOONER, THE
CYCLONE WILL BEGIN TO WEAKEN. DURING THIS PERIOD, MODEL TRACK
GUIDANCE BECOMES MORE UNCERTAIN DUE TO DIFFERENCES IN THE TIMING AND
DEGREE OF RE-CURVATURE AROUND THE STR AXIS. FOR THIS REASON, THERE
IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.//
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