Tropical Storm EWINIAR Advisory Mon Sep 24

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 19W (NINETEEN)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 19W, LOCATED APPROXIMATELY 400 NM
SOUTH-SOUTHWEST OF IWO-TO, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT
14 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS AN ELONGATED AND EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) WITH DISPLACED DEEP CONVECTION OVER THE SOUTHERN SEMI-
CIRCLE. A 232242Z SSMIS 91 GHZ MICROWAVE IMAGE DEPICTS AN ELONGATED
BUT DEFINED LLCC WITH CONVECTIVE BANDING OVER THE SOUTHERN SEMI-
CIRCLE. A 231408Z OSCAT IMAGE DEPICTS A DEFINED CIRCULATION WITH 25-
TO 30-KNOT WINDS DISPLACED TO THE EAST OF THE SYSTEM NEAR THE
CONVECTION. THE WINDS OVER THE WESTERN SEMI-CIRCLE REMAIN LIGHT
SHOWING ONLY 5 TO 10 KNOTS. INITIAL POSITION IS BASED UPON THE MSI
DUE TO THE EXPOSED LLCC. INITIAL INTENSITY IS BASED UPON 25 KNOT
DVORAK ESTIMATES FROM PGTW, RJTD, AND KNES. UPPER-LEVEL ANALYSIS
SHOWS THAT WESTERLY VERTICAL WIND SHEAR (VWS) REMAINS MODERATE (10-
20 KNOTS) BUT IS CONSIDERABLY HIGHER TO THE NORTH, THE SYSTEM ALSO
HAS POLEWARD OUTFLOW INTO A TUTT CELL TO THE EAST AND IS BEGINNING
TO DEVELOP SOME EQUATORWARD OUTFLOW. TD 19W IS TRACKING NORTH-
NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGE.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. TD 19W IS FORECASTED TO CONTINUE TO TRACK NORTH-NORTHWESTWARD
UNDER THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGE FOR THE NEXT
12 HOURS. BETWEEN TAU 12 AND TAU 24, TD 19W WILL ROUND THE
SUBTROPICAL RIDGE AXIS AND BEGIN A MORE NORTH-NORTHEASTWARD RUN. TD
19W WILL CONTINUE IN THIS DIRECTION UNTIL A DEEP SHORTWAVE TROUGH
WEAKENS THE RIDGE SLIGHTLY AND GIVES TD 19W A MORE POLEWARD TRACK.
AFTER THE TROUGH PROPAGATES EAST, THE RIDGE WILL BUILD BACK IN AND
TURN TD 19W TO THE NORTHEAST INTO THE HIGHER LATITUDES. TD 19W IS
FORECASTED TO SLOWLY INTENSIFY AS IT MOVES NORTH DUE TO IMPROVING
POLEWARD OUTFLOW. DYNAMIC MODELS ARE IN FAIRLY GOOD AGREEMENT WITH A
SMALL SPREAD THROUGH TAU 48. AFTER TAU 48, DURING THE POLEWARD TURN,
DUE TO THE TROUGH PASSAGE, MODELS SPREAD. OVERALL, THERE IS HIGH
CONFIDENCE IN THE EARLY TAUS.
   C. IN THE EXTENDED TAUS, TD 19W WILL RECURVE UPON THE BUILDING
RIDGE AND TRACK NORTH-NORTHEASTWARD AGAIN AND PICK UP SPEED. AS TD
19W APPROACHES THE HIGHER LATITUDES IT WILL ENCOUNTER HIGHER VWS AND
COOLER WATERS, WEAKENING THE SYSTEM. MODELS HAVE A LARGE SPREAD IN
THE EXTENDED TAUS, BUT GENERALLY KEEP THE SAME MOTION. DUE TO THE
WELL UNDERSTOOD ENVIRONMENT, FORECAST CONFIDENCE IS HIGH.//
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