Tropical Storm PRAPIROON Advisory Paz, 14.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 22W (PRAPIROON) WARNING NR 26//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 22W (PRAPIROON), LOCATED APPROXIMATELY 325 NM SOUTH-
SOUTHEAST OF KADENA AIR BASE, OKINAWA, JAPAN, HAS TRACKED EASTWARD
AT 02 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY SHOWS A SLIGHT LOSS OF CENTRAL CONVECTION WITH AN
EXPANSION OF THE BANDING DEEP CONVECTION. THE CURRENT INTENSITY IS
BASED ON THE MIX OF DVORAK ESTIMATES BETWEEN 65 TO 90 KNOTS. BASED
ON THE NOTED WEAKNESS IN CENTRAL CONVECTION, THE LOWER END OF THE
INTENSITY GUIDANCE WAS USED. THE CURRENT POSITION HAS BEEN DIFFICULT
TO ASSESS AS THE ORGANIZATION OF THE LOW LEVEL CIRCULATION CENTER
(LLCC) HAS BECOME OBSCURED IN THE EIR LOOP. A 131751Z AMSU-B
MICROWAVE IMAGE SUPPORTS THE POSITION BUT ALSO SUPPORTS THE OBSERVED
EXPANSION OF THE LLCC. UPPER LEVEL ANALYSIS INDICATES 22W IS LOCATED
IN A REGION OF WEAK (05-10 KNOTS) VERTICAL WIND SHEAR (VWS) WITH A
POINT SOURCE ANTICYCLONE LOCATED DIRECTLY OVER THE LLCC. ANIMATED
WATER VAPOR IMAGERY SHOWS AN UPPER-LEVEL SUBTROPICAL RIDGE (STR)
LOCATED OVER NORTHERN TAIWAN IS CREATING PRESSURE ALONG THE WESTERN
SIDE OF THE SYSTEM. STRONG ZONAL MID-LATITUDE FLOW OVER SOUTHERN
JAPAN IS HELPING SUPPORT A RECENT INCREASE IN POLEWARD OUTFLOW. TY
22W IS SLOWLY DRIFTING IN A WEAK STEERING ENVIRONMENT, UNDER THE
INFLUENCE OF A WEAKENING NEAR EQUATORIAL RIDGE (NER).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 22W IS EXPECTED TO SLOWLY TRACK ALONG THE NORTHERN EXTENT
OF THE NER AS A STR LOCATED TO THE NORTHEAST SLOWLY BUILDS TOWARDS
TY 22W. THE TRACK HAS BEEN KEPT SLOW WITH AN EXPECTED TURN TO THE
NORTHWEST AS THE STR BECOMES THE DOMINANT STEERING INFLUENCE AROUND
TAU 36. BETWEEN TAU 36 AND 72, THE STR IS EXPECTED TO CONTINUE
BUILDING TRACKING THE SYSTEM TO THE NORTHWEST TOWARDS THE STR AXIS.
AS TY 22W APPROACHES THE RIDGE AXIS, A MID-LATITUDE TROUGH IS
FORECAST TO WEAKEN THE WESTERN EXTENT OF THE STR, ALLOWING TY 22W TO
MOVE NORTH OF THE RIDGE AXIS AND START TRACKING NORTHEASTWARD. THE
INTENSITY IS EXPECTED TO INCREASE SLIGHTLY OVER THE NEXT 24 HOURS
AND PERSIST THROUGH TAU 72 DUE TO THE INCREASING POLEWARD OUTFLOW.
THE WESTERN PRESSURE ON THE SYSTEM WILL HINDER SIGNIFICANT
DEVELOPMENT.
   C. AS THE STEERING RIDGE ERODES AFTER TAU 72, TY 22W IS EXPECTED
TO ACCELERATE NORTHEASTWARD AND WEAKEN AS SEA SURFACE TEMPERATURES
DECREASE AND VWS INCREASES. BY TAU 120 TY PRAPIROON WILL BEGIN TO
INTERACT WITH THE BAROCLINIC ZONE AND BEGIN EXTRATROPICAL
TRANSITION. DYNAMIC MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT
WITH THE SLOW TRACK THROUGH TAU 48 AND THE MULTIPLE TURNS. THERE IS
SOME DISAGREEMENT WITH THE SPEED OF THE SYSTEM BEYOND TAU 48, WITH
NGPS AND ECMF SLOWER THAN GFS AND GFDN. THE CURRENT FORECAST FAVORS
SLIGHTLY FASTER THAN ECMF AND IS SLIGHTLY EASTWARD AND FASTER THAN
THE CONSENSUS OF ALL AVAILABLE MODEL GUIDANCE. DUE TO THE TIMING OF
THE TURNS ASSOCIATED WITH THE FORECAST AND THE SPEED OF MOVEMENT
DIFFERENCES AT THE EXTENDED TAUS IN AVAILABLE MODEL GUIDANCE, THE
CONFIDENCE IN THE TRACK REMAINS LOW.//
NNNN
NNNN