Tropical Storm PRAPIROON Advisory Thu Oct 11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 22W (PRAPIROON) WARNING NR 15//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 22W (PRAPIROON), LOCATED APPROXIMATELY 420 NM SOUTH OF
KADENA AIR BASE, OKINAWA, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT
06 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY AND AN 110018Z SSMIS MICROWAVE IMAGE DEPICT A WELL-DEFINED
LOW-LEVEL CIRCULATION CENTER (LLCC) WITH TIGHTLY-CURVED BANDING.
ANIMATED WATER VAPOR IMAGERY SHOWS RADIAL OUTFLOW CONTINUES TO BE
ENHANCED BY STRONG WESTERLY FLOW TO THE NORTH. THE INITIAL INTENSITY
IS BASED ON DVORAK INTENSITY ESTIMATES OF 90 KNOTS FROM PGTW AND
KNES. THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION BASED ON AN
EYE FEATURE IN THE SSMIS IMAGERY. UPPER LEVEL ANALYSIS INDICATES THE
SYSTEM IS BENEATH A POINT SOURCE ANTICYCLONE IN AN AREA OF LOW (05-
10 KNOT) VERTICAL WIND SHEAR (VWS). A TOTAL PRECIPITABLE WATER LOOP
INDICATES A VERY NARROW BAND OF SLIGHTLY DRYER AIR WRAPPING INTO THE
WESTERN AND SOUTHERN HALVES OF THE SYSTEM, POTENTIALLY COUNTERACTING
THE OTHERWISE VERY FAVORABLE ENVIRONMENTAL CONDITIONS. THE CYCLONE
IS TRACKING SLOWLY ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP-
LAYERED SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 22W IS EXPECTED TO BEGIN TRACKING MORE NORTHWARD DURING THE
NEXT 12 HOURS AS THE SYSTEM ENCOUNTERS STEERING INFLUENCES FROM TWO
SEPARATE RIDGES. THE RECENTLY WEAKENED SUBTROPICAL RIDGE (STR) TO
THE EAST WILL REMAIN THE DOMINANT INFLUENCE WHILE THE BUILDING NEAR
EQUATORIAL RIDGE (NER) TO THE SOUTHEAST WILL BRIEFLY CONTRIBUTE TO A
NORTHWARD COMPONENT OF TY 22W’S TRACK. BETWEEN TAUS 12 AND 24 TY 22W
IS EXPECTED TO SLOWLY RECURVE AROUND THE WESTERN EXTENT OF THE
WEAKENED STR TO THE EAST AND TAKE ON A NORTHEASTWARD TRACK THROUGH
TAU 72. TY 22W HAS THE POTENTIAL TO INCREASE IN INTENSITY DURING THE
NEXT 48 HOURS AS IT REMAINS IN A AN ENVIRONMENT WITH LOW VWS,
FAVORABLE SEA SURFACE TEMPERATURES, AND FAVORABLE OUTFLOW. ALTHOUGH
DYNAMIC MODEL GUIDANCE IS IN AGREEMENT WITH AN EVENTUAL CURVE TO THE
NORTHEAST, TIMING REMAINS INCONSISTENT BETWEEN MEMBERS. THE JTWC
TRACK FORECAST REMAINS SLIGHTLY EAST OF CONSENSUS TO OFFSET THE
UNLIKELY FAR WESTERN JGSM SOLUTION. FROM TAU 36 THROUGH 72 THE
FORECAST TRACK IS SLIGHTLY WEST OF CONSENSUS TO OFFSET GFDN, WHICH
HAS BEEN THE RIGHTMOST OUTLIER FOR THE PAST SEVERAL RUNS.
   C. AFTER TAU 72, TY PRAPIROON IS EXPECTED TO CONTINUE SLOWLY
TRACKING ALONG THE WESTERN PERIPHERY OF THE STR. DECREASING OCEAN
HEAT CONTENT AND INCREASING VERTICAL WIND SHEAR WILL RESULT IN A
GRADUAL REDUCTION IN INTENSITY. SPREAD IN DYNAMIC MODEL GUIDANCE
INCREASES AFTER TAU 72, WITH NOGAPS, GFDN, AND WBAR FAVORING A
FASTER AND MORE EASTERLY TRACK AND JGSM, ECMWF, AND EGRR INDICATING
A SLOWER AND MORE WESTERLY TRACK. THE JTWC FORECAST IS SIMILAR TO
THE PREVIOUS FORECAST, WITH HIGH CONFIDENCE IN INTENSITY AND TRACK
DURING THE EARLY TAUS BUT LOW CONFIDENCE IN LATER TAUS.//
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