Tropical Storm MALAKAS Advisory 17 Σεπ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (MALAKAS) WARNING NR 21//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 18W (MALAKAS), LOCATED APPROXIMATELY 185 NM SOUTHEAST OF
TAIPEI, TAIWAN HAS TRACKED NORTH-NORTHWESTWARD AT 08 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS
THAT TYPHOON 18W HAS MAINTAINED A WELL DEVELOPED, 10NM EYE OVER THE
PAST SIX HOURS. A 161723Z GCOM-W1 89 GHZ IMAGE DEPICTS AN IMPROVED
OVERALL CONVECTIVE SIGNATURE AND CONFIRMS THE WELL DEFINED 10 NM EYE
FEATURE, THOUGH THE MAJORITY OF THE DEEP CONVECTION IS LOCATED IN
THE SOUTHEASTERN QUADRANTS OF THE SYSTEM. THE INITIAL POSITION IS
BASED ON SATELLITE EYE FIXES FROM PGTW AND RJTD WITH GOOD
CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED AT 115 KNOTS AND IS
BASED ON DVORAK INTENSITY ESTIMATES T6.0 (115 KTS) FROM ALL
AGENCIES. UPPER-LEVEL ANALYSIS SHOWS A STRONG POINT SOURCE DIRECTLY
ABOVE THE SYSTEM, RESULTING IN RADIAL OUTFLOW SUPPORTING THE
CONTINUED INTENSIFICATION. SEA SURFACE TEMPERATURES ARE CURRENTLY
VERY FAVORABLE NEAR 29 TO 30 CELSIUS. TY MALAKAS IS TRACKING NORTH-
NORTHWESTWARD ALONG THE PERIPHERY OF A DEEP-LAYERED SUBTROPICAL
RIDGE CENTERED FAR TO THE TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 18W IS FORECAST TO CONTINUE TO TRACK GENERALLY NORTHWARD
OVER THE NEXT 24 HOURS AS IT APPROACHES THE AXIS OF A DEEP-LAYER
STEERING RIDGE CENTERED TO THE EAST-NORTHEAST. TROCHODIAL EYE MOTION
WILL RESULT IN NEAR TERM VARIABILITY IN THE TRACK, BUT OVERALL
MOTION WILL REMAIN NORTHWARD. BEYOND TAU 24 TY 18W WILL ROUND THE
RIDGE AXIS AND BEGIN TO TRACK NORTHEASTWARD AS THE STEERING RIDGE
RECEDES EASTWARD AHEAD OF A MAJOR SHORTWAVE TROUGH APPROACHING FROM
THE WEST, ACCELERATING AFTER TAU 48. THE POINT SOURCE ALOFT IS
FORECAST TO REMAIN ENTRENCHED OVER TOP OF TY 18W FOR THE NEXT 12
HOURS, HELPING THE SYSTEM TO MAINTAIN INTENSITY IN THE NEAR TERM.
AFTER TAU 12, THE POINT SOURCE DISSIPATES, CHOKING OFF THE
EQUATORWARD OUTFLOW CHANNEL RESULTING IN A WEAKENING TREND THROUGH
TAU 48. BETWEEN TAUS 48 AND 72, THE SYSTEM WILL BEGIN TO TAP INTO
THE STRONG POLEWARD OUTFLOW CHANNEL ASSOCIATED WITH THE MID-LATITUDE
WESTERLY FLOW, WHICH WILL ALLOW THE SYSTEM TO MAINTAIN INTENSITY FOR
SHORT PERIOD THROUGH TAU 72 BEFORE ENCOUNTERING INCREASING VERTICAL
WIND SHEAR.
   C. IN THE EXTENDED TAUS, TY 18W WILL ACCELERATE TOWARDS THE
NORTHEAST, MAKING LANDFALL IN SOUTHERN KYUSHU BETWEEN TAU 72 AND 96,
WEAKENING RAPIDLY AS IT ENCOUNTERS HIGH VERTICAL WIND SHEAR
ASSOCIATED WITH THE MID-LATITUDE WESTERLY JET AND LAND INTERACTION
EFFECTS. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 48,
WITH INCREASING UNCERTAINTY IN THE ALONG-TRACK SPEEDS AFTER TAU 72.
THE CURRENT TRACK FORECAST LIES NEAR THE MULTI-MODEL CONSENSUS,
WHICH DEPICTS SLIGHTLY SLOWER TRACK SPEEDS IN THE EXTENDED PERIOD
COMPARED TO THE PREVIOUS CONSENSUS FORECAST. GIVEN THE NOTED MODEL
UNCERTAINTY, THERE IS LOW CONFIDENCE IN THE EXTENDED TRACK
FORECAST.//
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