Tropical Storm BOLAVEN Advisory 23.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (BOLAVEN) WARNING NR 13//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 16W (BOLAVEN), LOCATED APPROXIMATELY 580 NM
SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WESTWARD AT 05
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY SHOWS THAT A VERY LARGE CENTRAL DENSE OVERCAST PERSISTS OVER
THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 230039Z AMSU-B 89 GHZ
MICROWAVE IMAGE REVEALS THAT THE MAJORITY OF DEEP CONVECTION IS
CONFINED TO THE SOUTHERN AND EASTERN SECTORS OF THE TY. THE CURRENT
POSITION IS BASED ON THE AMSU-B IMAGE WITH GOOD CONFIDENCE. THE
CURRENT INTENSITY IS BASED ON THE HIGHER RANGE OF DVORAK ESTIMATES
BETWEEN 77 TO 90 KNOTS. UPPER-LEVEL ANALYSIS INDICATES THAT TY 16W
IS APPROXIMATELY TWO DEGREES WEST OF THE NORTHWESTERN PACIFIC
EXTENSION OF THE SUBTROPICAL RIDGE (STR) AXIS WITH THE CENTER
ANCHORED EAST OF JAPAN. THE ORIENTATION OF THIS AMPLIFIED STR AXIS
IS NORTHEAST-SOUTHWEST AND TY 16W IS CURRENTLY STEERING ALONG ITS
SOUTHERN PERIPHERY. ALTHOUGH A SELF-INDUCED MESO-ANTICYCLONE STILLS
EXISTS OVER THE LLCC, TROPICAL UPPER-TROPOSPHERIC TROUGHING TO THE
NORTH IS CAUSING STRONG (30 KNOTS) NORTHERLY VERTICAL WIND SHEAR
(VWS) AND CONVERGENT PRESSURE ON THIS SIDE, AS NOTICED IN THE AMSU-B
IMAGE. EQUATORWARD OUTFLOW REMAINS ROBUST DUE TO SPEED DIVERGENCE
AND VWS IS WEAKER (05-10 KNOTS) OVER THE SOUTHEASTERN PORTION OF THE
LLCC.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. AS THE MID-LATITUDE TROUGH PROPAGATES OUT OF THE REGION WELL
NORTHEAST OF JAPAN, THE STEERING STR WILL REGAIN ZONAL ORIENTATION
AND STEER TY 16W NORTHWESTWARD ALONG ITS SOUTHERN PERIPHERY.
CONTINUED INTENSIFICATION IS EXPECTED AS SEA SURFACE TEMPERATURES
AND OCEAN HEAT CONTENT REMAIN FAVORABLE ALONG WITH THE STRONG
EQUATORWARD OUTFLOW. THE ONLY MECHANISM HOLDING BACK INTENSIFICATION
IS A LACK OF POLEWARD OUTFLOW. TY 16W IS A VERY LARGE SYSTEM THAT
SHOULD BE ABLE TO MODIFY THE STEERING RIDGE DUE TO INCREASED BETA-
EFFECT PROPAGATION IN RELATION TO ITS SIZE. THE PEAK INTENSITY
SHOULD OCCUR BEFORE LANDFALL OVER OKINAWA AND IMPACT THE ISLAND AS A
VERY INTENSE TYPHOON. ADDITIONALLY, BY TAU 72 ANOTHER TRANSITORY MID-
LATITUDE TROUGH WILL BE PROPAGATING EASTWARDS FROM EASTERN CHINA.
THIS TROUGH WILL AID IN THE EROSION OF THE STR'S WESTERN FLANK AND
ALLOW TY 16W TO TRACK MORE POLEWARD.
   C. IN THE EXTENDED FORECAST TY BOLAVEN SHOULD TRACK NORTH-
NORTHWESTWARD INTO THE WEAKNESS CAUSED BY THE PREVIOUSLY MENTIONED
TROUGH. TRACK SPEEDS WILL ACCELERATE DURING THIS TIME AND INTENSITY
WILL BE ON THE DECLINE AS OCEAN PARAMETERS BECOME LESS FAVORABLE.
HOWEVER, AN INCREASE OF POLEWARD OUTFLOW SHOULD BE ABLE TO SLIGHTLY
OFFSET THE COOLER OCEAN TEMPERATURES AND ALLOW TY 16W TO MAINTAIN
TYPHOON STRENGTH INTO THE SOUTHERN YELLOW SEA. ADDITIONALLY, VWS
SHOULD INCREASE AS THE SYSTEM EMBEDS FURTHER INTO THE TROUGH AND
UPPER-LEVEL WESTERLIES. OBJECTIVE AID GUIDANCE IS IN EXCELLENT
AGREEMENT UP TO OKINAWA. AFTER THIS POINT THE GUIDANCE SPREAD
INCREASES DUE TO VARIOUS DEPICTIONS OF TROUGH INTERACTION AND SYSTEM
STRENGTH. DURING THIS TIME THE ECMWF WAS FAVORED AS IT WAS IN CLOSE
AGREEMENT WITH THE MODEL CONSENSUS. THERE REMAINS HIGH CONFIDENCE IN
THE TRACK FORECAST DUE TO THE TIGHT ENVELOPE OF GUIDANCE.//
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