Tropical Storm NANGKA Advisory Thu Jul 16

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (NANGKA) WARNING NR 51//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 11W (NANGKA), LOCATED APPROXIMATELY 233 NM SOUTHEAST OF
IWAKUNI, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 12 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS
THE SYSTEM HAS DEGRADED AS CONVECTIVE BANDS WEAKENED. THE SYSTEM HAS
ALSO LOST SYMMETRY EVEN AS IT MAINTAINED A RAGGED 35-NM EYE. THE
INITIAL POSITION IS BASED ON THE MSI LOOP AND LINES UP WELL WITH A
CENTRAL WARM SPOT ON THE 152211 37V SSMIS MICROWAVE IMAGE. THE
INITIAL INTENSITY OF 70 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF
DVORAK ESTIMATES FROM ALL AGENCIES AND REFLECTS THE WEAKENING STAGE
OF THE SYSTEM. UPPER LEVEL ANALYSIS INDICATES A LESS FAVORABLE
ENVIRONMENT WITH INCREASING VERTICAL WIND SHEAR (15-20 KNOTS).
HOWEVER EXCELLENT
DIVERGENT OUTFLOW CONTINUES TO PROVIDE VENTILATION TO THE WEAKENING
CONVECTION. TY 11W IS TRACKING NORTH-NORTHWESTWARD UNDER AN EXTENSION
OF THE STEERING SUB-TROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 11W WILL TRACK NORTH-NORTHWESTWARD ALONG THE WESTERN
EXTENSION OF THE STEERING STR THROUGH TAU 24. AFTERWARDS, IT WILL
RECURVE NORTHEASTWARD AS IT ROUNDS THE EDGE AND ACCELERATES ON THE
POLEWARD SIDE OF THE STR. THE SYSTEM WILL MAKE LANDFALL OVER SHIKOKU
SHORTLY AFTER TAU 12 WHICH WILL BEGIN A RAPID WEAKENING TREND DUE TO
THE ADDITION OF LAND INTERACTION. AFTER TAU 24, TY 11W WILL EXIT INTO
THE SEA OF JAPAN AS A WEAK TROPICAL STORM AND TURN TO THE NORTHEAST
AS IT ROUNDS THE STR. THE RAPID DECAY WILL BE FURTHER EXACERBATED BY
COLDER SSTS AND HIGH VWS.
   C. IN THE EXTENDED TAUS, TY NANGKA WILL CONTINUE TO ACCELERATE TO
THE NORTHEAST AND CROSS THE NORTHERN TIP OF HONSHU NEAR MISAWA, AND
BACK INTO THE PACIFIC OCEAN. POOR ENVIRONMENTAL CONDITIONS WILL
CONTINUE TO WEAKEN THE SYSTEM LEADING TO ITS DISSIPATION BY THE END
OF THE FORECAST PERIOD. AVAILABLE MODEL GUIDANCE REMAINS IN GOOD
AGREEMENT OVER LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK.//
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