WDPN31 PGTW 301500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W WARNING NR 02//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
A. TROPICAL STORM (TS) 16W, LOCATED APPROXIMATELY 515 NM EAST-
SOUTHEAST OF IWO TO, HAS TRACKED NORTH-NORTHEASTWARD AT 18 KNOTS
OVER THE PAST SIX HOURS. ANIMATED INFRARED (IR) SATELLITE IMAGERY
SHOWS THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS CONSOLIDATED
WITHIN THE PAST SIX HOURS WITH INCREASED DEEP CENTRAL CONVECTION. A
031053Z ASCAT PASS DEPICTS A TIGHTLY WRAPPED LLCC WITH UP TO 40-KNOT
WINDS NEAR THE CENTER. THE INITIAL POSITION IS BASED ON THE IR AND
THE ASCAT WITH LOW CONFIDENCE. THE INITIAL INTENSITY IS BASED ON THE
ASCAT PASS. EQUATORWARD OUTFLOW AND OUTFLOW TO THE NORTHEAST ARE
FAVORABLE. HOWEVER, A TROPICAL UPPER TROPOSPHERIC TROUGH IS LIMITING
OUTFLOW ALONG THE WESTERN PERIPHERY.
3. FORECAST REASONING.
A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE.
B. TS 16W HAS SIGNIFICANTLY INCREASED IN TRANSLATION SPEED AS IT
TRACKS ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL STEERING RIDGE,
WHICH HAS RECENTLY STRENGTHENED. THIS SHOULD REMAIN THE DOMINANT
STEERING INFLUENCE THROUGHOUT THE FORECAST PERIOD. TS 16W IS
FORECAST TO STEADILY INTENSIFY AS IT TRACKS OVER WARM WATER AND
MAINTAINS FAVORABLE OUTFLOW ALOFT.
C. AFTER TAU 72, TS 16W IS EXPECTED TO BEGIN TURNING
NORTHEASTWARD AS AN APPROACHING MID-LATITUDE TROUGH WEAKENS THE
STEERING RIDGE. THE SYSTEM WILL BEGIN TO WEAKEN DUE TO INCREASED
VERTICAL WIND SHEAR, ASSOCIATED WITH THE MID-LATITUDE WESTERLIES,
AND LOWER SEA SURFACE TEMPERATURES. BY TAU 120, THE SYSTEM WILL
COMPLETE EXTRA-TROPICAL TRANSITION. THE NUMERICAL MODEL GUIDANCE
TRACKS THE SYSTEM TOO QUICKLY NORTHWARD, DIRECTLY INTO A MID-LEVEL
RIDGE TO THE NORTH. THIS FORECAST FAVORS A SLOWER TRACK AND IS MORE
IN AGREEMENT WITH JGSM.//
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