Tropical Storm SAOLA Advisory сб, 21.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 27W (TWENTYSEVEN)
WARNING NR 05//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 27W (TWENTYSEVEN), LOCATED APPROXIMATELY
300 NM EAST-SOUTHEAST OF ROTA, HAS TRACKED WEST-NORTHWESTWARD AT 08
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS AN EXPOSED, WELL-DEFINED LOW-LEVEL CIRCULATION
CENTER (LLCC) WITH ISOLATED DEEP CONVECTION FLARING OVER THE WEST
QUADRANT OF THE LLCC AND BROADER FRAGMENTED BANDING OVER THE
NORTHERN SEMI-CIRCLE. MSI SUPPORTS THE INITIAL POSITION WITH GOOD
CONFIDENCE. A 201525Z AMSR-2 89GHZ IMAGE SHOWS WEAK DEEP CONVECTIVE
BANDING DISPLACED OVER THE NORTHERN SEMI-CIRCLE AND SHALLOW BANDING
OVER THE SOUTHERN SEMI-CIRCLE WRAPPING INTO A WEAKLY DEFINED CENTER.
THE INITIAL INTENSITY IS ASSESSED AT 30 KNOTS BASED ON DVORAK
INTENSITY ESTIMATES OF T2.0 (30 KNOTS) FROM PGTW AND KNES. UPPER-
LEVEL ANALYSIS INDICATES MODERATE (15 TO 20 KNOTS) SOUTHEASTERLY
VERTICAL WIND SHEAR OFFSET BY DIFFLUENCE ALOFT, ENHANCED BY A
WEAKENING TUTT CELL NEAR 25N 155E. TD 27W IS TRACKING SLOWLY
WESTWARD WITHIN A COMPETING STEERING ENVIRONMENT.
3. FORECAST REASONING.
   A. THIS FORECAST ALONG WITH THE PREVIOUS FORECAST (20/12Z)
REPRESENT A SIGNIFICANT CHANGE IN FORECAST PHILOSOPHY WITH A SLOW
WESTWARD TRACK EXPECTED AND SLOW DEVELOPMENT.
   B. TD 27W IS POSITIONED WITHIN A COMPETING STEERING ENVIRONMENT
WITH A LOW-LEVEL (700MB) SUBTROPICAL RIDGE TO THE NORTH AND
NORTHEAST, AND A NEAR-EQUATORIAL RIDGE (NER) TO THE WEST AND
SOUTHWEST. A RECENT GUAM UPPER-AIR SOUNDING SUPPORTS THE PRESENCE OF
THE NER POSITIONED WEST OF GUAM WITH NORTH TO NORTHWEST WINDS AT 850-
500MB, WHICH MAINTAINS RESULTING IN A SLOW WESTWARD TO WEST-
SOUTHWESTWARD TRACK THROUGH TAU 72. THE TUTT CELL TO THE NORTH,
WHICH IS CURRENTLY AIDING OUTFLOW, IS FORECAST TO WEAKEN WITH WEAK
EASTERLY DIFFLUENT FLOW AND INCREASING VERTICAL WIND SHEAR
PERSISTING OVER THE SYSTEM THROUGH TAU 48 TO 72. THIS WILL LIMIT
INTENSIFICATION. DYNAMIC AIDS ARE IN FAIR AGREEMENT WITH SOLUTIONS
TRACKING 27W SLOWLY WEST-NORTHWESTWARD TO SOUTHWESTWARD.
   C. IN THE EXTENDED PERIOD, TD 27W, IF IT SURVIVES THE MARGINAL
UPPER-LEVEL CONDITIONS, IS FORECAST TO ACCELERATE WEST-NORTHWESTWARD
AS THE NER WEAKENS AND RECEDES EQUATORWARD, AND THE SUBTROPICAL
STEERING RIDGE BECOMES THE DOMINANT STEERING INFLUENCE. TD 27W IS
EXPECTED TO SLOWLY INTENSIFY AS UPPER-LEVEL DIFFLUENCE IMPROVES.
OVERALL, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST DUE TO
UNCERTAINTY IN THE MODEL GUIDANCE AND COMPLEX STEERING ENVIRONMENT.//
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