Tropical Storm YUTU Advisory Sun Oct 21

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 31W (THIRTYONE)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 31W (THIRTYONE), LOCATED APPROXIMATELY
812 NM EAST-SOUTHEAST OF ANDERSEN AFB, GUAM, HAS TRACKED WESTWARD AT
12 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY SHOWS AN AREA OF DEEP AND SPIRALING CONVECTION
WHICH CONTINUES TO CONSOLIDATE. THE INITIAL POSITION IS PLACED WITH
FAIR CONFIDENCE AND IS BASED ON A 211200Z HIMAWARI INFRARED SATELLITE
IMAGE. THE INITIAL INTENSITY OF 25 KNOTS IS BASED ON DVORAK INTENSITY
ESTIMATES OF T1.5 (25 KNOTS) FROM PGTW, KNES AND RJTD ALONG WITH A
PARTIAL 211041Z METOP-B ASCAT IMAGE SHOWING 25 KNOT WINDS.
ENVIRONMENTAL ANALYSIS SHOWS THAT TD 31W IS EXPERIENCING FAVORABLE
VERTICAL WIND SHEAR (5 TO 10 KNOTS) ALONG WITH IMPROVING RADIAL
OUTFLOW. SEA SURFACE TEMPERATURES ARE ALSO FAVORABLE FOR DEVELOPMENT,
BETWEEN 30 AND 32 DEGREES CELSIUS. TD 31W IS TRACKING WESTWARD ALONG
THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) LOCATED TO
THE NORTHEAST.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING MESSAGE FOR THIS
SYSTEM AND SETS THE FORECAST PHILOSOPHY.
   B. THROUGH TAU 72, TD 31W WILL TRACK TO THE NORTHWEST ALONG THE
SOUTHWESTERN EDGE OF THE AFOREMENTIONED STR. ENVIRONMENTAL CONDITIONS
(VERTICAL WIND SHEAR, UPPER LEVEL OUTFLOW, AND SEA SURFACE
TEMPERATURES) WILL ALL REMAIN FAVORABLE AND ALLOW FOR TD 31W TO
STEADILY INCREASE IN INTENSITY. BY TAU 72, TD 31W WILL REACH AN
INTENSITY OF 110 KNOTS. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT TD 31W WILL TRACK NORTHWESTWARD THROUGH TAU 72. HOWEVER, MODEL
GUIDANCE CONTINUES TO DIVERGE FROM THE INITIAL POSITION WITH A SPREAD
OF 270 NM BY TAU 72. THEREFORE, THERE IS LOW CONFIDENCE IN THIS
PORTION OF THE JTWC FORECAST TRACK.
   C. BEYOND TAU 72, TD 31W WILL BEGIN TO TURN NORTHWARD DUE TO A
WEAKNESS IN THE STR. TD 31W WILL STILL EXPERIENCE FAVORABLE
ENVIRONMENTAL CONDITIONS AND WILL REACH A PEAK INTENSITY OF 125 KNOTS
BY TAU 96 AND MAINTAIN THAT INTENSITY THROUGH TAU 120. THE PEAK
INTENSITY WILL OCCUR AS TD 31W ROUNDS THE WESTERN EDGE OF THE STR TO
THE EAST AND BEGINS TO TAP INTO ENHANCED POLEWARD OUTFLOW AND TRAVEL
OVER WATER WITH HIGH OCEAN HEAT CONTENT. DYNAMIC MODEL GUIDANCE IS IN
POOR AGREEMENT WITH AFUM INDICATING A NORTHWESTWARD TRACK WHILE GFS
IS INDICATING A RECURVE SCENARIO WITH A DIFFERENCE BETWEEN THOSE
MODELS OF 720 NM BY TAU 120. THE JTWC FORECAST TRACK IS PLACED NEAR
THE MULTIMODEL CONSENSUS. DUE TO THE DIFFERENCES IN MODEL GUIDANCE
THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.//
NNNN
NNNN