Tropical Storm PRAPIROON Advisory dom, 14-10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 22W (PRAPIROON) WARNING NR 27//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 22W (PRAPIROON), LOCATED APPROXIMATELY 295 NM SOUTH-
SOUTHEAST OF KADENA AIR BASE, OKINAWA, JAPAN, HAS TRACKED NORTH-
NORTHEASTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY SHOWS THE LOW LEVEL CIRCULATION
CENTER (LLCC) IS LOCATED UNDER A WEAKLY DEVELOPING BAND OF
CONVECTION WITHIN THE BROADER OUTER BANDING ALONG THE WESTERN AND
NORTHERN SIDES OF THE SYSTEM. A 132341Z SSMIS PASS SHOWS THE EYEWALL
HAS BEEN BREAKING DOWN OVER THE PAST 12 HOURS, WITH THE STRONGEST
CONVECTION LOCATED ALONG THE NORTHERN PERIPHERY. THE CURRENT
INTENSITY OF 65 KNOTS IS BASED ON THE STEADY WEAKENING TREND
OBSERVED IN DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD ALL RANGING
FROM 65 TO 75 KNOTS. 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 THE 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 BUILD AS AN
APPROACHING MID-LATITUDE TROUGH REORIENTS THE STR HELPING TO SHIFT
THE TRACK TO THE NORTHEAST AROUND THE STR AXIS. THE INTENSITY IS
EXPECTED TO MAINTAIN OVER THE NEXT 36 HOURS AS THE SYSTEM SLOWLY
TRACKS TOWARDS THE STR AXIS. INTENSITY GUIDANCE INDICATES A SLIGHT
INCREASE BETWEEN TAU 36 AND 48 AS INCREASED VENTILATION INTO THE MID-
LATITUDE FLOW HELPS TO INTENSIFY THE SYSTEM. THIS IS EXPECTED TO BE
SHORT-LIVED AS THE MID-LATITUDE FLOW BEGINS TO INCREASE VWS OVER THE
LLCC ALONG THE NORTHWESTERN QUADRANT, STIFLING THE POLEWARD OUTFLOW
CHANNEL.
   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 SHIFTED DRASTICALLY OVER THE
PAST SIX HOURS, WITH ECMF, NGPS, JGSM, AND GFS SHOWING A SHARP
WESTWARD TURN IN THE NEXT 12 HOURS. WBAR AND GFDN CONTINUE TO SHOW A
GENERALLY NORTHWARD TRACK. LOOKING AT THE MODEL FIELDS SUGGESTS THE
SYSTEM WILL MAKE A SLIGHT NORTHWESTWARD TURN ASSOCIATED WITH THE
BUILDING STR, HOWEVER THE CURRENT FORECAST TEMPERS THE SEVERITY OF
THIS TURN BASED ON THE DRASTIC SHIFT IN MODEL GUIDANCE OVER THE PAST
SIX HOURS. THE FORECAST KEEPS TO THE EAST OF CONSENSUS AND FASTER IN
THE LATER TAUS BASED ON THE STRONG SHIFT IN MODEL GUIDANCE TO THE
WEST. THERE HAS BEEN A SLIGHT SHIFT WESTWARD FROM THE PREVIOUS
FORECAST, AND BASED ON THE RECENT LARGE VARIATION IN GUIDANCE THE
CONFIDENCE IN THE TRACK REMAINS LOW.//
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