Tropical Storm DUJUAN Advisory Mon Sep 21

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (TWENTYONE)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 21W (TWENTYONE), LOCATED APPROXIMATELY
214 NM NORTHWEST OF NAVSTA GUAM, HAS TRACKED WESTWARD AT 10 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED IR SATELLITE SHOWS
PERSISTENT SYMMETRICAL DEEP CONVECTION AS WELL AS A LOW LEVER
SPINNER TO THE EAST. DUE TO THE MULTIPLE VORTICES PRESENT, THERE IS
LOW CONFIDENCE IN THE INITIAL POSITIONING OF THE SYSTEM WHICH IS
PLACED AT THE CENROID OF THE VORTICES. HOWEVER, DUE TO THE
CONVECTIVE STRUCTURE AND AN OLDER 211246Z RSCAT IMAGE, THERE IS GOOD
CONFIDENCE IN THE INITIAL INTENSITY OF 25 KNOTS. UPPER LEVEL
ANALYSIS SHOWS THAT THERE IS 10 TO 20 KNOTS OF VWS OFFSET BY GOOD
DIVERGENCE ALOFT. THE SYSTEM IS CURRENTLY TRACKING ON THE SOUTHERN
SIDE OF A STR TO THE NORTH.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. TD 21W WILL CONTINUE TO TRACK TO THE WEST UNDER THE INFLUENCE
OF THE STR THROUGH TAU 36. BEYOND THAT, A SHORTWAVE THROUGH WILL
CAUSE A SMALL BREAK IN THE STR AND ALLOW TD 21W TO TAKE A MORE
POLEWARD TRACK. EXPECT MARGINAL INTENSIFICATION THROUGH TAU 48 AS
THE SYSTEM CONTINUES TO CONSOLIDATE. HOWEVER THE SYSTEM IS EXPECTED
TO EXCEED TYPHOON STRENGTH BY TAU 72.
   C. IN THE EXTENDED FORECAST, TD 21W WILL CONTINUE TO INTENSIFY AS
POLEWARD OUTFLOW IMPROVES. THE SYSTEM WILL CONTINUE TO TRACK TO THE
NORTHWEST THROUGH A BREAK IN THE RIDGE. DYNAMIC MODEL GUIDANCE IS
VARIED WITH REGARD TO BOTH THE SPEED OF TRACK AND THE POINT AT WHICH
THE BREAK IN THE RIDGE DEVELOPS. AS SUCH, THERE IS LIMITED
CONFIDENCE IN THE JTWC FORECAST TRACK AT THIS TIME.//
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