WTPN33 PGTW 060300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 11W (ELEVEN) WARNING
NR 002//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION 11W (ELEVEN), LOCATED APPROXIMATELY
202 NM NORTHWEST OF SAIPAN, HAS TRACKED NORTHWESTWARD AT 10 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS AN ELONGATED, PARTIALLY EXPOSED LOW LEVEL CIRCULATION
(LLC) WITH DEEP CONVECTION PREDOMINANTLY IN THE SOUTHERN PORTION OF
THE CIRCULATION. A 052044Z PARTIAL SSMIS 89GHZ MICROWAVE IMAGE
DEPICTS A BROAD BUT DISORGANIZED AREA OF LOW LEVEL TURNING, WITH DEEP
CONVECTION TO THE SOUTH. THE INITIAL POSITION IS PLACED WITH LOW
CONFIDENCE LARGELY DUE TO THE BROAD NATURE OF THE CIRCULATION. THE
SYSTEM IS STILL EXHIBITING MONSOON DEPRESSION CHARACTERISTICS WITH AN
EXPANSIVE WIND FIELD. THE INITIAL INTENSITY OF 30 KTS IS BASED ON A
052345Z METOP-B ASCAT PASS MISS THAT SHOWED AN EXPANSIVE AREA OF 25
KT WINDS AND SOME 30 KT WIND BARBS OVER 150 NM TO THE EAST AND IS
SLIGHTLY HIGHER THAN THE PGTW AND RJTD DVORAK CURRENT INTENSITY
ESTIMATES OF T1.0-1.5 (25 KTS). ENVIRONMENTAL CONDITIONS FOR TD 11W
ARE MARGINAL WITH EXCELLENT EQUATORWARD OUTFLOW AND WARM SEA SURFACE
TEMPERATURES (28-30 CELSIUS) BEING OFFSET BY MODERATE TO STRONG
VERTICAL WIND SHEAR (VWS) (15-25 KTS). TD 11W IS TRACKING WESTWARD
ALONG THE SOUTHWESTERN PERIPHERY OF A RIDGE TO THE NORTH.
3. FORECAST REASONING.
A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
B. TD 11W IS FORECAST TO CONTINUE NORTHWESTWARD THROUGH TAU 48 AS
A SUBTROPICAL RIDGE BUILDS IN FROM THE EAST. THE SYSTEM WILL CONTINUE
TO TRACK NORTHWEST THROUGH TAU 36 BEFORE TURNING NORTHWARD AS IT
ROUNDS THE STR AXIS. DURING THIS PERIOD, DECREASING VERTICAL WIND
SHEAR AND EXCELLENT OUTFLOW ALOFT WILL ALLOW A STEADY INTENSIFICATION
OF THE SYSTEM, REACHING 70 KNOTS BY TAU 72. HOWEVER, SLOW TRACK
MOTION AND LOW OCEAN HEAT CONTENT (OHC) DESPITE HIGH SSTS WILL LIMIT
OVERALL INTENSIFICATION. MODEL UNCERTAINTY DURING THIS PERIOD HAS
NARROWED; MOST SHOW AN EITHER NORTHWARD OR NORTHWESTWARD TRACK IN THE
SHORT TERM. THE OFFICIAL JTWC TRACK FORECAST CLOSELY FOLLOWS THE
CONSENSUS TRACK IN THE NEAR TERM WITH LOW CONFIDENCE.
C. AFTER TAU 72, TD 11W IS FORECAST TO TRACK NORTH-NORTHEASTWARD
ALONG THE NORTHWESTERN PERIPHERY OF THE STR. A SHORTWAVE TROUGH
PASSES THROUGH THE AREA AND ERODES THE STR TO THE EAST, ALLOWING THE
SYSTEM TO RECURVE AFTER TAU 72 IN SOME MODELS. THE SYSTEM WILL PASS
CLOSE TO IWO TO BETWEEN TAU 72-96. AFTER TAU 96, LOW OHC AND SLIGHTLY
INCREASED VERTICAL WIND SHEAR MAY BEGIN A SLOW WEAKENING TREND.
HOWEVER, OUTFLOW WILL BE ENHANCED BY THE PASSING TROUGH AND MAY
MAINTAIN INTENSITY FOR LONGER. THE JTWC INTENSITY FORECAST IS PLACED
SIGNIFICANTLY ABOVE THE INTENSITY CONSENSUS IN LIGHT OF THE EXPECTED
INCREASED DIVERGENCE ALOFT DUE TO THE TROUGH. MODEL GUIDANCE BEYOND
TAU 72 SPREADS SIGNIFICANTLY. GFS AND ECMWF BEGIN TO VEER THE SYSTEM
TO THE NORTHWEST AFTER TAU 96 BASED ON INDUCED RIDGING BUILDING TO
THE NORTH BETWEEN TWO TROUGHS, WHILE NAVGEM AND THE GFS ENSEMBLE HAVE
THE SYSTEM RECURVING TO THE NORTHEAST AS THE TROUGH PUSHES THE STR TO
THE EAST OUT OF THE WAY. BASED ON THE SYNOPTIC SITUATION, THE
OFFICIAL FORECAST IS A SLIGHT NORTHEAST RECURVE. HOWEVER, BASED ON
THE SIGNIFICANT MODEL SPREAD, THERE IS LOW CONFIDENCE IN THE JTWC
TRACK FORECAST, ESPECIALLY IF THE RIDGING TO THE NORTH BUILDS IN AS
DISPLAYED IN THE ECMWF AND GFS SOLUTIONS.//
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