#26 Postby Chacor » Mon Aug 18, 2008 10:16 am
WDPN31 PGTW 181500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 13W WARNING NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
A. THE SYSTEM WAS UPGRADED TO A TYPHOON AT 18/12Z BASED ON IMPROVED
CONSOLIDATION, TIGHTLY CURVED BANDING AND A DEFINED MICROWAVE EYE
FEATURE ON THE 180647Z TMI 37H IMAGE. ANIMATED WATER VAPOR IMAGERY
SHOWS A STRENGTHENING ANTICYCLONE OVER THE CENTER PROVIDING IMPROVED
EQUATORWARD OUTFLOW, PARTICULARLY OVER THE EAST AND SOUTHEAST QUA-
DRANT...POLEWARD OUTFLOW HAS REMAINED WEAK BUT HAS NOT PREVENTED THE
SYSTEM FROM RAPIDLY INTENSIFYING (30 KNOTS) OVER THE PAST 24 HOURS.
TYPHOON (TY) 13W HAS CONTINUED TO TRACK QUICKLY WESTWARD. IN GENERAL,
THE DYNAMIC MODELS HAVE TRENDED TOWARD A STRONGER SUBTROPICAL RIDGE
AND A WEAKER MIDLATITUDE SHORTWAVE TROUGH OVER THE PAST FEW RUNS.
CONSEQUENTLY, THE MODEL TRACKERS HAVE SHIFTED SIGNIFICANTLY WEST
OVER THE PAST 12 HOURS. ADDITIONALLY, THERE ARE MORE MODEL AIDS
AVAILABLE TO INCLUDE SUPERIOR PERFORMERS LIKE THE ECMWF MODEL.
B. TY 13W CONTINUES TO TRACK WESTWARD UNDER THE STEERING INFLUENCE
OF THE MID-LEVEL SUBTROPICAL RIDGE POSITIONED NORTH OF THE SYSTEM.
THE 18/00Z 500MB ANALYSIS CONTINUES TO SHOW A HIGH CENTERED OVER
OKINAWA WITH A BROAD RIDGE EXTENDING WESTWARD INTO SOUTHEASTERN
CHINA. ANIMATED WATER VAPOR IMAGERY ALSO SHOWS A STRONG RIDGE
MAINTAINING WITH THE MIDLATITUDE SHORTWAVE FILLING AND TRACKING
OVER THE RIDGE INTO THE KOREAN PENINSULA. RIDGING IS EVIDENT OVER
CENTRAL CHINA WITH A DEFORMATION ZONE NEAR SHANGHAI. THE CURRENT
POSITION IS BASED ON A WELL-DEFINED LLCC WITH HIGH CONFIDENCE IN
POSITION AND MOTION. THE CURRENT INTENSITY IS BASED ON THE HIGH
END OF DVORAK ESTIMATES RANGING FROM 55 TO 65 KNOTS DUE TO THE
IMPROVED CONSOLIDATION.
3. FORECAST REASONING
A. THE FORECAST TRACK WAS SHIFTED WEST OF TAIWAN SINCE THE PREVIOUS
WARNING.
B. THIS SHIFT IS BASED ON A NUMBER OF FACTORS. THE PRIMARY REASON
IS THAT THE STR HAS REMAINED STRONG AND CONTINUES TO DRIVE THE
SYSTEM QUICKLY WESTWARD. ADDITIONALLY, THE MIDLATITUDE TROUGH IS
FILLING AND IS MOVING OVER THE TOP OF THE STR. THE MODEL FIELDS
ARE DEPICTING A STRONG STR MAINTAINING THROUGH AT LEAST TAU 48
AND THE ONLY MODELS EAST OF TAIWAN ARE THE POOREST PERFORMERS
STATISTICALLY THUS FAR. PLUS NOGAPS SHOWS CLEAR PROBLEMS WITH
EXCESSIVE, FALSE INTERACTION WITH A MIDLATITUDE SURFACE TROUGH
WHICH IS CAUSING A SHARP POLEWARD TURN AFTER TAU 72. TY 13W IS
FORECAST TO TRACK WESTWARD TO WEST-NORTHWESTWARD THROUGH TAU 72.
THE BULK OF THE DYNAMIC AIDS ARE IN AGREEMENT WITH THIS FORECAST
AND THE FORECAST IS BASED ON A CONSENSUS OF THE DYNAMIC AIDS. TY
13W IS FORECAST TO RAPIDLY INTENSIFY THROUGH TAU 36 WITH FURTHER
SIGNIFICANT INTENSIFICATION UNLIKELY DUE TO LAND INTERACTION.
IMPROVED POLEWARD OUTFLOW AFTER TAU 36, SHOULD ALLOW THE SYSTEM
TO INTENSIFY SLOWLY OR MAINTAIN INTENSITY.
C. THERE IS A LARGE DEGREE OF UNCERTAINTY IN THE EXTENDED FORECAST DUE
TO DIFFERENCES IN HOW EACH MODEL HANDLES THE WEAKENING OF THE STR.
WITH THE EXCEPTION OF NOGAPS AND TC-LAPS, ALL THE OTHER MODELS INDIC-
ATE RECURVATURE WEST OF TAIWAN WITH THE RIDGE DEPICTED STRONGER AND
MAINTAINING LONGER NORTH OF THE SYSTEM. AN EXAMINATION OF NOGAPS
SLP FIELDS SHOWS EXCESSIVE INTERACTION OF THE VORTEX WITH A MIDLATIT-
UDE TROUGH THEREFORE THE TRACKER IS SUSPECT. IT IS POSSIBLE THAT
TY 13W WILL TRACK ON A MORE WEST-NORTHWESTWARD TRACK THAN THE CURRENT
FORECAST REFLECTS. TY 13W SHOULD MAKE LANDFALL OVER THE SOUTHEAST
CHINA COAST NEAR TAU 96.
FORECAST TEAM: DELTA//
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