Tropical Storm HAISHEN Advisory 31.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 11W (ELEVEN) WARNING
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 11W (ELEVEN), LOCATED APPROXIMATELY 272 NM
EAST-SOUTHEAST OF IWO TO, JAPAN, HAS TRACKED SOUTHWESTWARD AT 12 KNOTS
(KTS) OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS CONVECTIVE BANDING WRAPPING UNDER FLARING DEEP
CONVECTION OVERHEAD THE LOW LEVEL CIRCULATION CENTER (LLCC). A 311107Z
ASCAT-A IMAGE DEPICTS A SLIGHTLY ELONGATED CIRCULATION WITH A SWATH OF
25-30 KT WINDS DISPLACED WITHIN THE DEEP CONVECTION TO THE SOUTHEAST
OF THE LLCC AND WEAKER (15-20 KT) WINDS ELSEWHERE. BASED ON THE
AFOREMENTIONED ASCAT IMAGE ALONG WITH DVORAK CURRENT INTENSITY
ESTIMATES OF T1.0-2.0 (25-30 KTS) BY PGTW, RJTD, AND KNES, THE INITIAL
INTENSITY IS SET AT 25 KTS WITH GOOD CONFIDENCE. ENVIRONMENTAL
ANALYSIS REVEALS THAT TD 11W IS SUPPORTED BY ROBUST EQUATORWARD UPPER
LEVEL OUTFLOW AND WARM (30-31 CELSIUS) SEA SURFACE TEMPERATURES (SST)
THAT ARE BEING OFFSET BY MODERATE (20-25 KT) VERTICAL WIND SHEAR
(VWS). OF NOTE, TD 11W IS CURRENTLY TRACKING SOUTHWESTWARD UNDER THE
COMBINED STEERING INFLUENCE OF A SUBTROPICAL RIDGE (STR) TO THE WEST
AND AN EXTENSION OF THE STR TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING MESSAGE FOR THIS SYSTEM
AND SETS THE FORECAST PHILOSOPHY.
   B. IN THE NEAR-TERM, TD 11W WILL TRACK WEST-SOUTHWESTWARD UNDER THE
COMBINED STEERING INFLUENCE OF THE STR TO THE WEST AND THE STR
EXTENSION. DURING THIS TIME, THE SYSTEM WILL EXPERIENCE FAVORABLE SST
AND CONTINUED DIVERGENCE ALOFT, BUT INTENSIFICATION WILL BE LIMITED
DUE TO HIGH VWS VALUES. CONSEQUENTLY, TD 11W IS EXPECTED TO GRADUALLY
INTENSIFY TO 40 KTS BY TAU 24. AS A MIDLATITUDE SHORTWAVE TROUGH
APPROACHES FROM THE WEST, THE STR TO THE WEST WILL BEGIN TO ERODE
WHILE THE STR TO THE NORTHEAST WILL BUILD, BECOMING THE PRIMARY
STEERING MECHANISM. UNDER ITS INFLUENCE, THE SYSTEM WILL SLOWLY TURN
WESTWARD THEN NORTHWESTWARD THROUGH TAU 72 AS IT TRACKS ALONG THE
PERIPHERY. VWS VALUES DECREASE AFTER TAU 24 ALLOWING TD 11W TO
STEADILY INTENSIFY ALONG THE FORECAST TRACK. NUMERICAL MODEL GUIDANCE
IS IN FAIR AGREEMENT WITH THE GFS AND UKMET ENSEMBLE SOLUTIONS AS
OUTLIERS TO THE SOUTH AND THE JGSM SOLUTION TO THE NORTH. THE JTWC
FORECAST TRACK IS PLACED NEAR THE MULTI-MODEL CONSENSUS WITH FAIR
CONFIDENCE. ADDITIONALLY, THE ECMWF ENSEMBLE IS IN GOOD AGREEMENT WITH
SPREAD SLOWLY INCREASING IN THE LATER TAUS.
   C. IN THE EXTENDED PERIOD, THE SYSTEM WILL CONTINUE TO TRACK
NORTHWARD ALONG THE PERIPHERY OF A STR TO THE EAST. THE SYSTEM WILL
STEADILY INTENSIFY TO 85 KTS BY TAU 120 DUE TO CONTINUED FAVORABLE
ENVIRONMENTAL CONDITIONS OF LOW VWS, WARM SST, AND CONDUCIVE OCEAN
HEAT CONTENT VALUES. HOWEVER, NUMERICAL MODEL GUIDANCE DIVERGES
THROUGHOUT THE FORECAST PERIOD, INCREASING TO A CROSS TRACK SPREAD OF
228 NM BY TAU 120. THEREFORE, DUE TO THE UNCERTAINTY (LARGE SPREAD) IN
THE MODEL SOLUTIONS, THERE IS OVERALL FAIR CONFIDENCE IN THE JTWC
FORECAST TRACK WHICH IS PLACED ALONG THE MULTI-MODEL CONSENUS.//
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