Tropical Storm NANGKA Advisory 06.07.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (NANGKA) WARNING NR
11//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 11W (NANGKA), LOCATED APPROXIMATELY 132 NM
NORTHWEST OF UJELANG, HAS TRACKED WEST-NORTHWESTWARD AT 12 KNOTS
OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON RECENT
MULTISPECTRAL SATELLITE IMAGERY AND A 052332Z PGTW SATELLITE FIX.
THE INTENSITY OF 60 KNOTS IS CONSISTENT WITH A CONSENSUS OF DVORAK
SATELLITE INTENSITY ESTIMATES FROM MULTIPLE REPORTING AGENCIES.
RECENT ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS PERSISTENT
DEEP CONVECTION WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER
(LLCC), PARTICULARLY OVER THE EASTERN PORTION. THE SYSTEM HAS
STEADILY INTENSIFIED OVER THE PAST SIX HOURS, FUELED BY LOW VERTICAL
WIND SHEAR, PASSAGE OVER WARM WATER, AND IMPROVING OUTFLOW ENHANCED
BY A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL TO THE
NORTHEAST. TS 11W IS TRACKING ALONG THE PERIPHERY OF A SUBTROPICAL
STEERING RIDGE TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 11W WILL CONTINUE TRACKING ALONG THE SUBTROPICAL STEERING
RIDGE PERIPHERY THROUGH THE NEXT 72 HOURS. WESTWARD MOTION WILL
GRADUALLY TRANSITION TO A MORE NORTHWESTWARD TRACK AS THE STEERING
RIDGE REORIENTS AHEAD OF A DEVELOPING MID-LATITUDE TROUGH. CONTINUED
INTENSIFICATION IS EXPECTED AS VERTICAL WIND SHEAR REMAINS GENERALLY
FAVORABLE AND UPPER-LEVEL OUTFLOW IS ENHANCED BY THE TUTT CELL TO
THE NORTHEAST. A PERIOD OF RAPID INTENSIFICATION IN THE NEAR TO
MEDIUM TERM IS POSSIBLE AS UPPER LEVEL TROUGHING PROVIDES THE
POTENTIAL FOR SIGNIFICANTLY INCREASED OUTFLOW ALOFT. DYNAMIC MODEL
GUIDANCE REMAINS IN GENERALLY GOOD AGREEMENT REGARDING THE FORECAST
TRACK THROUGH TAU 72, WITH THE UKMET MODEL PRESENTING AS A POLEWARD
OUTLIER FROM THE PRIMARY MODEL GROUPING. THE CURRENT TRACK FORECAST
FOR THIS PERIOD LIES CLOSE TO THE MULTI-MODEL CONSENSUS AND THE
PREVIOUS JTWC FORECAST.
   C. IN THE EXTENDED PERIOD, STORM MOTION IS EXPECTED TO SLOW AS A
DEVELOPING MID-LATITUDE TROUGH BEGINS WEAKENING THE STEERING RIDGE.
FUTHER INTENSIFICATION IS ANTICIPATED AS ENVIRONMENTAL CONDITIONS
REMAIN FAVORABLE, PARTICULARLY WITH POLEWARD OUTFLOW POTENTIAL
IMPROVING AHEAD OF THE DEVELOPING MID-LATITUDE TROUGH. DYNAMIC MODEL
GUIDANCE HAS DIVERGED A BIT IN THE EXTENDED PERIOD AS EACH MODEL
PRESENTS A DIFFERENT DEPICTION OF THE ANTICIPATED SLOWING AND A
POTENTIAL POLEWARD TURN FOLLOWING TAU 120. HOWEVER, MODEL SPREAD
REMAINS SMALL ENOUGH, AND THE SYNOPTIC SITUATION IS SUFFICIENTLY
STRAIGHTFORWARD, TO LEND HIGH CONFIDENCE TO THE CURRENT JTWC
FORECAST TRACK.//
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