Tropical Storm KROVANH Advisory Wed Sep 16

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY)
WARNING NR 03//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 20W (TWENTY), LOCATED APPROXIMATELY 418
NM NORTHEAST OF ANDERSEN AFB, GUAM, HAS TRACKED WEST-NORTHWESTWARD
AT 09 KNOTS OVER THE PAST SIX HOURS. RECENT ANIMATED MSI DEPICTS
PERSISTENT DEEP CONVECTION ASSOCIATED WITH A PARTIALLY-EXPOSED LLCC.
A 150358Z NOAA-19 MICROWAVE IMAGE REVEALS THE BULK OF THE DEEP
CONVECTION OVER THE NORTHWESTERN QUADRANT WITH CURVED BANDS WRAPPING
INTO THE CENTER. THE CURRENT POSITION IS BASED ON THE MSI,
AFOREMENTIONED MICROWAVE IMAGE ALONG WITH SATELLITE FIXES FROM PGTW
AND RJTD WITH FAIR CONFIDENCE. THE INITIAL INTENSITY REMAINS AT 30
KNOTS BASED ON AN OVERALL ASSESSMENT OF DVORAK INTENSITY ESTIMATES
FROM ALL REPORTING AGENCIES. UPPER-LEVEL ANALYSIS INDICATES TD 20W
IS LOCATED IN A MARGINALLY-FAVORABLE ENVIRONMENT WITH LOW TO
MODERATE (10 TO 20 KNOT) VWS AND FAIR OUTFLOW. TD 20W IS CURRENTLY
TRACKING UNDER THE STEERING INFLUENCE OF A BUILDING STR TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TD 20W WILL CONTINUE TRACKING GENERALLY NORTHWESTWARD AS THE
STR BECOMES FIRMLY ESTABLISHED TO THE NORTH. SLOW INTENSIFICATION IS
EXPECTED IN THE NEAR-TERM AS MARGINALLY-FAVORABLE ENVIRONMENT
PERSISTS. AFTER TAU 36, UPPER-LEVEL CONDITIONS ARE FORECAST TO
IMPROVE ALLOWING THE SYSTEM TO STEADILY INTENSIFY.
   C. IN THE EXTENDED TAUS, TD 20W WILL ROUND THE STEERING RIDGE
AXIS AND ACCELERATE TOWARD THE MIDLATITUDE BAROCLINIC ZONE BY TAU
120. STEADY INTENSIFICATION IS EXPECTED AS THE SYSTEM MAKES THE
TURN, BUT INCREASING VWS AND PASSAGE OVER COOLER WATER WILL LIKELY
WEAKEN THE SYSTEM AND INITIATE THE FIRST STAGE OF EXTRATROPICAL
TRANSITION BY TAU 120. DYNAMIC MODEL GUIDANCE REMAINS IN GOOD
AGREEMENT REGARDING TIMING OF THE TURN AROUND TAU 72; HOWEVER, DUE
TO THE UNCERTAINTY IN THE INITIAL POSITIONING AND THE SPREAD AMONG
AVAILABLE TRACKERS IN THE EXTENDED TAUS, THERE IS OVERALL LOW
CONFIDENCE IN THE JTWC FORECAST.//
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