Tropical Storm NANGKA Advisory Tue Jul 14

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (NANGKA) WARNING NR 45//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 11W (NANGKA), LOCATED APPROXIMATELY 637 NM SOUTH-
SOUTHEAST OF IWAKUNI, JAPAN, HAS TRACKED NORTHWARD AT 07 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY SHOWS A 10NM EYE HAS RE-EMERGED; HOWEVER, A STRUGGLING
CONVECTIVE SIGNATURE CONTINUES DUE TO DRY AIR WRAPPING INTO THE
CENTER FROM THE NORTHERN AND WESTERN PERIPHERIES. A 140953Z SSMIS
91GHZ MICROWAVE IMAGE DEPICTS A 50 NM MICROWAVE EYE FEATURE WITH
LIMITED CONVECTION LOCATED ALONG THE NORTHERN EYEWALL AND WITHIN
BANDING ALONG THE EASTERN PERIPHERY. THE CURRENT POSITION IS BASED
ON THE EYE FEATURE IN THE EIR LOOP WITH HIGH CONFIDENCE. THE INITIAL
INTENSITY IS HELD AT 90 KNOTS BASED ON AN UNCHANGED CONVECTIVE
STRUCTURE AND SUPPORTED BY CONSENSUS DVORAK INTENSITY ESTIMATES OF
T5.0 (90 KNOTS) FROM ALL AGENCIES. TY NANGKA IS LOCATED IN A
MARGINALLY FAVORABLE ENVIRONMENT WITH LOW TO MODERATE (10-15 KNOT)
VERTICAL WIND SHEAR (VWS), EXCELLENT EQUATORWARD OUTFLOW ALOFT, AND
SEA SURFACE TEMPERATURES ABOVE 28 CELSIUS; HOWEVER, DRY AIR AND
SUBSIDENCE TO THE NORTH AND WEST ARE INHIBITING CONVECTIVE
DEVELOPMENT. TY 11W IS TRACKING ALONG THE WESTERN PERIPHERY OF THE
DEEP LAYERED SUB-TROPICAL RIDGE (STR) TO THE EAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 11W WILL CONTINUE TO TRACK POLEWARD ALONG THE WESTERN
PERIPHERY OF THE STEERING STR. BY TAU 24, THIS STR IS EXPECTED TO
REBUILD, FORCING TY NANGKA ON A WEST-NORTHWESTWARD TRAJECTORY.
ENVIRONMENTAL CONDITIONS WILL REMAIN MOSTLY UNCHANGED; HOWEVER, THE
DRY AIR AND SUBSIDENCE ALONG THE NORTHERN SIDE OF THE SYSTEM WILL
PREVENT AN INCREASED INTENSIFICATION RATE. BEYOND TAU 48, AS THE
SYSTEM GAINS LATITUDE, IT WILL LOSE THE EXCELLENT EQUATORWARD
OUTFLOW CHANNEL. IN ADDITION, INCREASING VWS, LOW OCEAN HEAT
CONTENT, AND LAND INTERACTION WILL BEGIN TO WEAKEN THE CYCLONE AS IT
APPROACHES AND MAKES LANDFALL ALONG THE SOUTHERN COAST OF JAPAN.
   C. BEYOND TAU 72, TY NANGKA WILL TRACK OVER THE SOUTHERN ISLANDS
OF JAPAN AND ROUND THE STR AXIS, TURNING TO A NORTHEASTWARD
TRAJECTORY. TY 11W WILL CONTINUE TO WEAKEN AS VWS RAPIDLY INCREASES
AND SEA SURFACE TEMPERATURE DECREASES, LEADING TO ITS DISSIPATION BY
THE END OF THE FORECAST PERIOD. DYNAMIC MODEL GUIDANCE HAS IMPROVED
REGARDING THE TIMING OF THE RECURVE WITH THE BULK OF GUIDANCE
SHOWING A 150NM SPREAD AT TAU 72. HOWEVER, DUE TO THE CONTINUED
SPREAD BEYOND TAU 72, THERE REMAINS LOW CONFIDENCE IN THE JTWC TRACK
FORECAST.//
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