Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Depression 10w/

From: SIU Weather Processor <[email-masked]>
Date: Thu, 2 Sep 2010 22:04:06 -0500

WDPN33 PGTW 030300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 10W/
WARNING NR 06//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL DEPRESSION (TD) 10W (TEN), LOCATED APPROXIMATELY 340
NM SOUTHEAST OF OKINAWA, JAPAN, HAS TRACKED NORTHWESTWARD AT 17 KTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL IMAGERY SHOWS THAT
THE SYSTEM CONTINUES TO STRUGGLE DEVELOPING IN THE VICINITY OF THE
TROPICAL UPPER TROPOSHERIC TROUGH (TUTT) TO THE WEST. FLARING, DEEP
CONVECTION IS EVIDENT OVER THE LOW LEVEL CIRCULATION CENTER (LLCC),
BUT ONLY WEAK INFLOW BANDING IS SEEN ON THE SOUTHERN SIDE. WATER
VAPOR IMAGERY SHOWS THAT THE SYSTEM HAS SOME OUTFLOW TO THE EAST,
BUT THAT THE TUTT IS IMPINGING ON THE OUTFLOW TO THE SOUTH AND WEST.
A 022303Z SSMIS PASS SHOWS THAT THE SYSTEM HAS A SYMMETRICAL LLCC
AND A SMALL POCKET OF DEEP CONVECTION NEAR THE CENTER. THE SYSTEM IS
CURRENTLY TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE TO THE NORTHEAST. POSITION IS BASED ON THE 022303Z
SSMIS PASS AND A POSITION FIX FROM PGTW WITH GOOD CONFIDENCE.
INTENSITY IS BASED ON A DVORAK INTENSITY FIX FROM PGTW.
3. FORECAST REASONING.
   A. THE EXTENDED PORTION OF THE FORECAST IS NOW MORE TO THE WEST
OF THE TRACK FORECAST AT 021800Z IN RESPONSE TO A WESTERN FINGER OF
THE SUBTROPICAL RIDGE. THE INITIAL HALF OF THE FORECAST IS
FUNDAMENTALLY THE SAME.
   B. TD 10W WILL CONTINUE TRACKING ALONG THE SOUTHWESTERN PERIPHERY
OF A DEEP SUBTROPICAL RIDGE ENTRENCHED JUST SOUTH OF MAINLAND JAPAN
AND IT SHOULD CONTINUE TO TRACK NORTHWESTWARD THROUGH TAU 36. EARLY
NUMERICAL MODEL GUIDANCE IS SPLIT ON HOW THE SYSTEM WILL BEHAVE IN
THE FIRST 24 HOURS, WITH ECMWF, GFS AND UKMET TRACKING THE SYSTEM
MORE WESTWARD IN WHAT IS BELIEVED TO BE EXCESSIVE DIRECT INTERACTION
WITH THE TUTT TO THE WEST. NOGAPS AND WBAR HAVE A TRACK THAT CLOSER
APPROXIMATES THE SHAPE OF THE RIDGE TO THE NORTH. BETWEEN HOURS 36
AND 72 THE SYSTEM IS EXPECTED TO SLOW AND JOG TO THE WEST IN
RESPONSE TO THE WESTERN EXTENT OF THE RIDGE THAT EXTENDS ACROSS THE
MOUTH OF THE YELLOW SEA, WITH THE POSSIBILITY OF WEAKENING DUE TO
COLDER WATER, REDUCED OUTFLOW, AND MILD VERTICAL WIND SHEAR FROM THE
UPPER-LEVEL RIDGE. ALL OF THE MODELS WITH THE EXCEPTION OF UKMET
(WHICH LOSES THE CIRCULATION AT 48 HOURS) AGREE WITH THIS MOTION,
BUT IN VARYING DEGREES.
   C. AFTER TAU 72, TD 10W IS EXPECTED TO MEANDER INTO THE YELLOW
SEA AS THE WESTERN EXTENT OF THE RIDGE BREAKS DOWN IN RESPONSE TO A
PASSING MID-LATITUDE TROUGH. THE BAROCLINIC ZONE IS FORECASTED TO BE
NEAR THE NORTHERN EXTENT OF THE YELLOW SEA, AND AS THE RIDGE TO THE
EAST RECEDES FROM THE EARLIER MID-LATITUDE TROUGH, THE SYSTEM WILL
BE LEFT IN A RELATIVELY WEAK STEERING ENVIRONMENT. THE SYSTEM IS
EXPECTED TO CONTINUE TO WEAKEN IN THE COOLER WATERS IN THE NORTHERN
YELLOW SEA AND START TO FEEL THE VERTICAL WINDSHEAR FROM THE
BAROCLINIC ZONE. NUMERICAL MODEL GUIDANCE ALL SUPPORTS THE WEAK
STEERING ENVIRONMENT, AND AS EXPECTED IN A WEAK ENVIRONMENT, THERE
ARE MANY POSSIBLE SOLUTIONS, BUT ALL THE MODELS HAVE IT IN THE
YELLOW SEA.//

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