Tropical Storm YUTU Advisory Mon Oct 22

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W (YUTU)
WARNING NR 03//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 31W (YUTU), LOCATED APPROXIMATELY 706 NM EAST-
SOUTHEAST OF ANDERSEN AFB, HAS TRACKED WEST-NORTHWESTWARD AT 10
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY SHOWS DEEP CONVECTION WITH IMPROVED SPIRAL BANDING WRAPPING
AROUND A SOMEWHAT ELONGATED LOW-LEVEL CIRCULATION CENTER (LLCC).
THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON A
212314Z METOP-A 89GHZ MICROWAVE IMAGE, WHICH IS BETWEEN THE PGTW
FIX TO THE WEST AND KNES FIX TO THE EAST. THE 212316Z ASCAT
SCATTEROMETER WINDS INDICATE THAT THE WESTERN PERIPHERY OF THE
ELONGATED LLCC IS TOWARD THE PGTW FIX, WHEREAS THE DEEPEST
CONVECTION TO THE EAST WRAPPING AROUND THE MID-LEVEL CIRCULATION IS
CLOSER TO THE KNES FIX. ALL OF THIS EVIDENCE SUGGESTS THAT THE LLCC
IS SOMEWHAT ELONGATED FROM THE WEST TO EAST WITH SOME SLIGHT VORTEX
TILING DOWNSHEAR. TS 31W IS EXPERIENCING SOME LIGHT WESTERLY
VERTICAL WIND SHEAR (10-15 KNOTS), BUT WITH EXCELLENT AND IMPROVING
OUTFLOW AS THE TUTT CELL TO THE NORTHWEST GRADUALLY FILLS AND
DEAMPLIFIES. SEA SURFACE TEMPERATURES REMAIN WARM (30 TO 32 DEGREES
CELSIUS), AND THE SYSTEM IS EXPECTED TO TRAVERSE A FAVORABLE
ENVIRONMENT THAT IS CONDUCIVE FOR INTENSIFICATION AS IT TRACKS
TOWARD THE NORTHWEST AROUND THE SOUTHWESTERN PERIPHERY OF A
SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. THE INTENSITY FORECAST WITHIN TAU 48 WAS INCREASED TO ACCOUNT
FOR THE LIKELIHOOD OF RAPID INTENSIFICATION, BUT OTHERWISE, THERE
IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. THROUGH TAU 72, TS 31W WILL CONTINUE TRACKING TOWARD THE
NORTHWEST AROUND THE STR, WITH ENVIRONMENTAL CONDITIONS REMAINING
FAVORABLE FOR INTENSIFICATION. AS THE WEAK TUTT CELL TO THE
NORTHWEST FILLS, POLEWARD OUTFLOW IS EXPECTED TO DRAMATICALLY
IMPROVE, AND A PERIOD OF RAPID INTENSIFICATION IS LIKELY BETWEEN
TAUS 12 AND 48. BY TAU 72, TS 31W WILL REACH AN INTENSITY OF AT
LEAST 110 KNOTS. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT THAT
TS 31W WILL TRACK NORTHWESTWARD THROUGH TAU 72, SO THERE IS HIGH
CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.
   C. BEYOND TAU 72, A WEAKNESS IN THE STR INDUCED BY AN UPPER-
TROPOSPHERIC TROUGH WILL GRADUALLY TURN TS 31W SLIGHTLY MORE
POLEWARD. HOWEVER, THERE IS STILL A SIGNIFICANT SPREAD IN THE
DYNAMIC MODEL GUIDANCE IN THESE EXTENDED TAUS, WITH THE GFS-RELATED
MODEL SUITE (AVNO, AEMN, HWRF) RECURVING THE SYSTEM TOWARD THE
NORTH AWAY FROM THE MARIANAS. THE REST OF THE CONW GUIDANCE TRACKS
THE SYSTEM TOWARD AND THROUGH THE NORTHERN MARIANAS, SO THE JTWC
FORECAST TRACK IS SLIGHTLY WEST OF CONW. ENVIRONMENTAL CONDITIONS
ARE EXPECTED TO REMAIN FAVORABLE FOR INTENSIFICATION, AND TS 31W IS
FORECAST TO REACH SUPER TYPHOON INTENSITY BY THE END OF THE
FORECAST PERIOD. THE FORECAST OF 135 KNOTS AT TAU 120 IS ACTUALLY
SLIGHTLY LOWER THAN ICNW, SO DEPENDING ON WHETHER RAPID
INTENSIFICATION OCCURS IN THE SHORT TERM, THE POSSIBILITY EXISTS THAT
TS 31W WILL BECOME EVEN MORE INTENSE THAN CURRENTLY FORECAST. DUE TO
THE SIGNIFICANT SPREAD IN THE MODEL GUIDANCE AT THESE EXTENDED TAUS,
THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST
TRACK.//
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