Tropical Storm PHANFONE Advisory Fri Oct 03

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (PHANFONE) WARNING NR 18//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 18W (PHANFONE), LOCATED APPROXIMATELY 350 NM WEST-
SOUTHWEST OF IWO TO, HAS TRACKED NORTHWESTWARD AT 08 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
INDICATES A RAGGED EYE FEATURE, AND THUS WELL DEFINED LOW LEVEL
CIRCULATION CENTER.  ADDITIONALLY, A 022123Z SSMIS MICROWAVE IMAGE
DEPICTS A LARGE EYE (ABOUT 50NM IN DIAMETER) FEATURE.  THE INITIAL
POSITION IS BASED ON BOTH THE MSI AND MICROWAVE IMAGE WITH GOOD
CONFIDENCE. THE MICROWAVE IMAGE, ALTHOUGH LOWER RESOLUTION THAN
OTHER SENSORS, SEEMS TO INDICATE COMPLETION OF THE POSSIBLE EYEWALL
REPLACEMENT CYCLE (ERC). HOWEVER, A HIGHER RESOLUTION MICROWAVE
PASS IS REQUIRED TO VERIFY THE PROCESS. THE INITIAL INTENSITY
REMAINS AT 110 KNOTS BASED ON DVORAK CURRENT INTENSITY ESTIMATES
AND POSSIBILITY OF AN ERC OCCURRING.  ANIMATED WATER VAPOR IMAGERY
DEPICTS A GOOD POLEWARD CHANNEL, AND CONTINUED, ALBEIT SLIGHTLY
DECREASED, RADIAL OUTFLOW. TY 18W WILL CONTINUE TO TRACK TO THE
NORTH-NORTHWEST ALONG THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL
RIDGE (STR) TOWARDS A WEAKNESS CREATED BY A DEEP MIDLATITUDE
SHORTWAVE TROUGH POSITIONED THROUGH THE YELLOW SEA.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY
FROM THE PREVIOUS PROGNOSTIC REASONING BULLETIN.
   B. TY 18W IS EXPECTED TO CONTINUE TURNING POLEWARD OVER THE NEXT
48 HOURS AS THE AFOREMENTIONED MIDLATITUDE TROUGH TRACKS TO THE
EAST. PHANFONE IS EXPECTED TO CREST THE STR AXIS BY TAU 36 AND
START ITS NORTH TO NORTHEASTWARD  RECURVATURE. NUMERICAL MODEL
TRACK FORECAST GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 36. THE
MAXIMUM INTENSITY HAS BEEN LOWERED TO 120 KNOTS AS THE SYSTEM
ROUNDS THE STR AXIS DUE TO SOME COLD AIR ADVECTION VISIBLE ALREADY
IN THE WATER VAPOR LOOP PARTIALLY OFFSETTING FAVORABLE SEA SURFACE
CONDITIONS AND UPPER LEVEL ENVIRONMENT WITH LOW VERTICAL WIND SHEAR
(VWS) AND GOOD POLEWARD OUTFLOW. BEYOND TAU 36, THERE IS SOME
UNCERTAINTY OF THE TRACK DUE TO A SPREAD IN THE MODELS, AND THUS
THE MULTI-MODEL CONSENSUS, WITH REGARD TO THE STRENGTH AND TIMING
OF THE MIDLATTITUDE TROUGH AND THUS THE BREAK IN THE STR. THE JTWC
FORECAST TRACK LAYS IN CLOSE ALIGNMENT WITH THIS CONSENSUS THROUGH
TAU 36 AND IS FASTER AND TO THE EAST DUE TO A KNOWN HISTORICAL BIAS
OF DYNAMIC MODELS WITH REGARD TO THE SPEED OF RECURVE SCENARIOS AND
EXTRATROPICAL TRANSITION (ETT). EXPECT THE INTENSITY OF PHANFONE TO
DECREASE BEYOND TAU 36 AS THE SYSTEM IS AFFECTED BY INCREASED VWS
DUE TO THE INTERACTION WITH THE MIDLATITUDE WESTERLIES AND A STRONG
BAROCLINIC ZONE POSITIONED OVER CENTRAL JAPAN. AFTER TAU 48, EXPECT
TY PHANFONE TO BEING ETT, AS THE SYSTEM BECOMES FURTHER EMBEDDED IN
THE MIDLATTITUDE WESTERIES.
   C. IN THE EXTENDED FORECAST PERIOD, TY 18W IS EXPECTED TO
COMPLETELY MERGE WITH THE APPROACHING MIDLATITUDE TROUGH,
ACCELERATING EAST-NORTHEASTWARD, AND COMPLETING ETT BY TAU 96. A
FURTHER EXPANSION OF THE WIND FIELD SHOULD BE EXPECTED, INCLUDING
GALE AND STORM FORCE WINDS, AS THE SYSTEM COMPLETES THIS
TRANSITION. THE CURRENT SYNOPTIC PATTERN, SPECIFICALLY OF THE UPPER
LEVEL TROUGH OVER THE SOUTH CHINA SEA, FAVORS THE DEVELOPMENT OF
VERY STRONG UPPER-LEVEL WESTERLY FLOW ALONG SOUTHEAST HONSHU, WHICH
ALIGNS WITH THE FORECAST OF RAPID ACCELERATION AND RECURVATURE.
HOWEVER, DUE TO THE LARGE VARIATIONS IN MODEL DEPICTIONS OF TRACK
SPEED AND THE RECURVE TIMELINE, THERE IS OVERALL LOW CONFIDENCE IN
THE EXTENDED TRACK FORECAST.//
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