Tropical Storm DUJUAN Advisory Wed Sep 23

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (DUJUAN) WARNING NR
08//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 21W (DUJUAN), LOCATED APPROXIMATELY 623 NM
SOUTHEAST OF KADENA AB, JAPAN HAS TRACKED WESTWARD AT 10
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY CONTINUES TO SHOW A BROAD AND ELONGATED CIRCULATION WITH AN
AREA OF DEEP CONVECTION ALONG THE WESTERN PERIPHERY. A 231151Z METOP-
A MICROWAVE INAGE FURTHER DEPICTS THE ELONGATED SHALLOW BANDING
FORMING THE LOW LEVEL CIRCULATION CENTER (LLCC). HOWEVER, A 231150Z
ASCAT BULLSEYE PROVIDES GOOD CONFIDENCE IN THE INITIAL POSITION AND
SUPPORTS THE INCREASE IN CURRENT INTENSITY TO 45 KNOTS. IN ADDITION,
THIS IMAGE WAS USED TO ADJUST THE CURRENT AND FORECASTED WIND RADII.
UPPER LEVEL ANALYSIS INDICATES A MARGINAL ENVIRONMENT WITH 20 TO 25
KNOT EASTERLY VERTICAL WIND SHEAR (VWS) KEEPING THE CONVECTION
OFFSET FROM THE LLCC. GOOD DIVERGENT OUTFLOW IS SUSTAINING THE
CURRENT CONVECTION. TS DUJUAN IS TRACKING ALONG THE SOUTHERN
PERIPHERY OF A DEEP LAYERED SUB-TROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 21W WILL CONTINUE TO TRACK WEST-NORTHWESTWARD OVER THE NEXT
24 HOURS AS THE STR REMAINS NORTH OF THE SYSTEM. CONCURRENTLY,
EXPECT MARGINAL INTENSIFICATION DUE TO MODERATE VWS CONTINUING TO
PREVENT THE SYSTEM FROM FULLY CONSOLIDATING. BEYOND TAU 24, A
SHORTWAVE MID-LATITUDE TROUGH WILL CREATE A SMALL BREAK IN THE STR,
ALLOWING TS 21W TO TURN MORE NORTHWESTWARD. DECREASED VWS AND
IMPROVED DIVERGENT OUTFLOW WILL INCREASE THE RATE OF INTENSIFICATION.
   C. IN THE EXTENDED TAUS, TS 21W WILL CONTINUE TO TRACK TOWARDS
THE WEAK BREAK IN THE STEERING STR AND MAINTAIN INTENSIFY AS VWS
INCREASES ONCE AGAIN AND OUTFLOW IS HAMPERED. DYNAMIC MODEL GUIDANCE
CONTINUES TO SHOW A TRIFURCATION. NAVGEM AND THE EUROPEAN MODELS
SHOW A WEAKER SYSTEM PASSING THROUGH THE SOUTHERN RYUKYU ISLANDS.
ENVIRONMENTAL CONDITIONS WILL SUPPORT AN INTENSIFICATION MAKING
THESE SOLUTIONS LESS REALISTIC. HWRF, COAMPS-TC, AND THE JAPANESE
MODELS SHOW A SHARP RECURVE BEFORE THE SYSTEM REACHES THE RYUKYU
ISLANDS. TS DUJUAN IS NOT FORECASTED TO BE STRONG ENOUGH IN THE NEAR
TERM TO BREAK THROUGH THE STEERING STR AND RECURVE NORTH. GFS, GFS
ENSEMBLE MEAN, AND GFDN SHOW A STRAIGHT NORTHWESTWARD TRACK PASSING
OVER OKINAWA WITH THE POSSIBILITY OF A LATER RECURVE. THIS SOLUTION
IS DEEMED MOST FEASIBLE AT THIS TIME BASED ON THE EXPECTED
DEVELOPMENT OF THE SYSTEM AND SUPPORTS THE CURRENT FORECAST TRACK.
THE AVAILABLE ENSEMBLE CLUSTERS ALSO CONTINUE TO SHOW ALL THREE
SOLUTIONS AS A POSSIBILITY LEADING TO FURTHER UNCERTAINTY. DUE TO
THE CONTINUED WIDE SPREAD AND INSTABILITY IN ALL MODEL GUIDANCE,
THERE IS LOW CONFIDENCE IN THE JTWC FORECAST.//
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