Tropical Storm PHANFONE Advisory 03 Οκτ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (PHANFONE) WARNING NR 17//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 18W (PHANFONE), LOCATED APPROXIMATELY 332 NM WEST-
SOUTHWEST OF IWO TO, HAS TRACKED NORTHWESTWARD AT 15 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
INDICATES A VERY SLIGHT WEAKENING OF THE SYSTEM, WITH A DRY MOAT
VISIBLE ON THE SOUTHERN PORTION OF THE LOW LEVEL CIRCULATION
CENTER. A 021731Z GPM MICROWAVE IMAGE DEPICTS A VERY SMALL
SHRINKING EYE IN THE NORTHERN PORTION OF THE MOAT. BASED ON THE
ABOVE MICROWAVE AND AN EARLIER 021605Z GCOMW1 IMAGE, A CLEAR
TROCHOIDAL MOVEMENT OF THE PINHOLE EYE OF THIS SYSTEM IS EVIDENT.
DESPITE THE EYE WOBBLE, THE INITIAL POSITION IS BASED ON THE
MICROWAVE IMAGES WITH VERY GOOD CONFIDENCE. ALL MICROWAVE IMAGES
APPEAR TO INDICATE FORMATION OF A SECONDARY EYEWALL AND SUGGESTS A
POSSIBLE EYEWALL REPLACEMENT CYCLE (ERC), WHICH MAY ACCOUNT FOR THE
APPARENT WEAKENING TREND IN THE PAST 24 HOURS. HOWEVER, THE INITIAL
INTENSITY IS ASSESSED TO REMAIN AT 110 KNOTS BASED ON DVORAK
CURRENT INTENSITY ESTIMATES AND POSSIBILITY OF AN ERC OCCURRING.
ANIMATED WATER VAPOR IMAGERY CONTINUES TO DEPICT EXCELLENT NEAR-
RADIAL OUTFLOW, PARTICULARLY THE POLEWARD CHANNEL. TY 18W CONTINUES
TO TURN NORTHWESTWARD AS IT TRACKS ALONG THE SOUTHWESTERN PERIPHERY
OF THE SUBTROPICAL RIDGE (STR) TOWARD A BROAD WEAKNESS CREATED BY A
DEEP MIDLATITUDE SHORTWAVE TROUGH POSITIONED OVER THE EAST CHINA
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, MAINTAINING THE BREAK IN THE STR. PHANFONE  IS EXPECTED TO
CREST THE STR AXIS BY TAU 48 AND START ITS NORTH TO NORTHEASTWARD
RECURVATURE. NUMERICAL MODEL TRACK FORECAST GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 36 WITH AN OVERALL TIGHTER ALIGNMENT.
ADDITIONALLY, EXPECT TY 18W TO REACH IS MAXIMUM INTENSITY OF 125
KNOTS AT THIS TIME AS THE SYSTEM SLOWS OVER FAVORABLE SEA SURFACE
CONDITIONS, AS WELL AS A FAVORABLE UPPER LEVEL ENVIRONMENT WITH LOW
VERTICAL WIND SHEAR (VWS) AND GOOD POLEWARD OUTFLOW. BEYOND TAU 36
THERE IS SOME UNCERTAINTY BASED OF THE TRACK BASED ON 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 REGARDS THE SPEED OF RECURVE
SCENARIOS AND EXTRATROPICAL TRANSITION (ETT). THE CURRENT TRACK IS
IN GOOD ALIGNMENT WITH THE PREVIOUS JTWC FORECAST TRACK. 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. BEYOND TAU 48 EXPECT COMMENCING ETT, JUST SOUTHEAST
OF KYOTO.
   C. IN THE EXTENDED FORECAST PERIOD, TY 18W IS EXPECTED TO MERGE
WITH THE APPROACHING MIDLATITUDE TROUGH, ACCELERATE EAST-
NORTHEASTWARD, AND COMPLETE ETT BY TAU 96. EXPECT AN EXPANSION OF
THE WIND FIELD, 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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