#244 Postby euro6208 » Wed Oct 24, 2018 9:33 am
WDPN31 PGTW 241500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 31W (YUTU) WARNING NR
13//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUPER TYPHOON 31W (YUTU), LOCATED APPROXIMATELY 43 NM SOUTH-
SOUTHEAST OF SAIPAN, HAS TRACKED NORTHWESTWARD AT 11 KNOTS OVER THE
PAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BY APPLYING A SLIGHT SOUTHWEST OFFSET TO THE CENTER OF A 20 NM ROUND
EYE IN THE 241200Z ENHANCED INFRARED SATELLITE IMAGE. THE EYE IS
SURROUNDED BY SYMMETRIC DEEP CONVECTION WITH THE DEEPEST CONVECTIVE
BANDS TO THE NORTH AND SOUTH. THE INITIAL INTENSITY OF 155 KNOTS IS
CONSISTENT WITH MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF
T7.5 (155 KTS). SAIPAN REPORTED AN 85 KNOT PEAK WIND GUST AT 241258Z
AND SUSTAINED NORTHEASTERLY WINDS OF OVER 50 KNOTS WERE REPORTED
BETWEEN 241200Z AND 241300Z. THE ENVIRONMENT IS FAVORABLE WITH
MODERATE (15-20 KNOT) VERTICAL WIND SHEAR (VWS), EXCELLENT POLEWARD
OUTFLOW, GOOD EQUATORWARD OUTFLOW, AND WARM (29-30 CELSIUS) SEA
SURFACE TEMPERATURE. THE CYCLONE IS TRACKING ALONG THE SOUTHWESTERN
PERIPHERY OF A SUBTROPICAL RIDGE (STR) TO THE NORTHEAST.
3. FORECAST REASONING.
A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. THE STR TO THE NORTHEAST IS EXPECTED TO CONTINUE STEERING STY
31W NORTHWESTWARD TO WEST-NORTHWESTWARD THROUGH TAU 72.
ENVIRONMENTAL CONDITIONS SHOULD MAINTAIN THE INTENSITY THROUGH TAU
36 BUT HIGHER VWS SHOULD BEGIN TO GRADUALLY WEAKEN THE SYSTEM
AFTERWARD. THE NUMERICAL MODELS ARE IN GOOD AGREEMENT THROUGH TAU 24
BEFORE THE SPREAD INCREASES SIGNIFICANTLY. BY TAU 72, THE SPREAD
BETWEEN THE NORTHERNMOST (NAVGEM) AND SOUTHERNMOST (JGSM) MEMBERS IS
AROUND 255 NM, THEREFORE UNCERTAINTY IS HIGH FOR THIS PORTION OF THE
FORECAST.
C. BEYOND TAU 72, STY 31W IS FORECASTED TO CONTINUE TRACKING WEST-
NORTHWESTWARD UNTIL A SLIGHT NORTHWARD TURN AS IT BEGINS TO ROUND
THE STR AXIS AROUND TAU 120. THROUGHOUT THE EXTENDED PERIOD, THE
CYCLONE IS EXPECTED TO CONTINUE GRADUALLY WEAKENING. FOR THE
EXTENDED PERIOD, THE GUIDANCE ENVELOPE IS HUGE WITH OVER 1000 NM OF
SPREAD BETWEEN THREE CLUSTERS BY TAU 120. THE SOUTHERN CLUSTER
CONSISTS OF THE UKMET, GALWEM, AND JGSM. THEY PREDICT A STR TO THE
NORTHWEST WILL BECOME THE DOMINANT STEERING INFLUENCE, CAUSING A
WESTWARD TO WEST-SOUTHWESTWARD TRACK. THE NORTHERN CLUSTER CONSISTS
OF NAVGEM AND COAMPS-GFS. THEY PREDICT RECURVATURE TO BEGIN AROUND
TAU 72 AS AN APPROACHING MID-LATITUDE TROUGH CAUSES A BREAK IN THE
STR. THE MIDDLE CLUSTER CONSISTS OF ECMWF, GFS, HWRF, AND THE ECMWF
AND GFS ENSEMBLE MEANS. FOR THE MOST PART, THIS CLUSTER PREDICTS A
SLIGHT NORTHWARD TURN BY TAU 120 AS A SECOND MID-LATITUDE TROUGH
CREATES A WEAKNESS IN THE STR. THE JTWC FORECAST TRACK FOLLOWS THE
MIDDLE CLUSTER AS THAT TRACK SEEMS MOST LIKELY, ESPECIALLY WHEN
FACTORING IN THE ECMWF ENSEMBLE TRACKS. OF THE OTHER TWO CLUSTERS,
THE MORE SOUTHERN TRACK SEEMS A MORE LIKELY ALTERNATIVE THAN THE
NORTHERN TRACK, ALTHOUGH BOTH ARE CERTAINLY POSSIBLY. BASED ON THE
SPREAD IN THE NUMERICAL GUIDANCE, UNCERTAINTY IS VERY HIGH FOR THE
EXTENDED PORTION OF THE JTWC FORECAST.//
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