Bullish first warning.
WDPN31 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION 20W (TWENTY), LOCATED APPROXIMATELY 118 NM
EAST OF ANDERSEN AFB, HAS TRACKED WESTWARD AT 16 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED SATELLITE IMAGERY DEPICTS DEEP
CONVECTION BUILDING AND BEGINNING TO WRAP INTO A CONSOLIDATING LOW
LEVEL CIRCULATION CENTER (LLCC). A 081702Z SSMI 85GHZ MICROWAVE
IMAGE SHOWS WELL DEFINED LOW LEVEL CLOUD LINES WRAPPING INTO THE
LLCC WITH FORMATIVE BANDING OVER THE EASTERN AND NORTHERN
PERIPHERY. THE CURRENT POSITION IS BASED ON THE WELL ASSESSED LLCC
IN THE PREVIOUSLY MENTIONED MICROWAVE IMAGERY, AS WELL AS RADAR FIX
DATA FROM THE PGUA NEXRAD SYSTEM SHOWING A FAIRLY WELL DEFINED
LLCC. THE INITIAL INTENSITY IS BASED ON A PREVIOUS PARTIAL ASCAT
PASS SHOWING 20-25 KNOT WINDS ALONG THE EASTERN PERIPHERY AND
CURRENT DVORAK INTENSITY ESTIMATES OF T1.0 (20-25 KNOTS) FROM PGTW.
TD 20W IS LOCATED IN A MARGINALLY FAVORABLE ENVIRONMENT WITH
EQUATORWARD OUTFLOW, LOW (5-10 KNOTS) VERTICAL WIND SHEAR (VWS),
AND SEA SURFACE TEMPERATURES (SSTS) OF 30-31 CELSIUS. THE
ENVIRONMENT IS OVERALL ASSESSED AS MARGINAL AT THIS TIME DUE TO THE
LACK OF CONSOLIDATION IN THE LOW LEVELS AND THE SINGLE OUTFLOW
CHANNEL. TD 20W IS TRACKING QUICKLY WESTWARD UNDER THE INFLUENCE OF
A SUB-TROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE
FORECAST PHILOSOPHY.
B. TD 20W WILL TRACK JUST NORTH OF DUE WEST FOR THE INITIAL 12
HOURS, BEFORE TURNING WEST-NORTHWESTWARD AFTER TAU 12, UNDER THE
INFLUENCE OF THE DEEP-LAYER STR TO THE NORTH THROUGH. VWS AND SSTS
REMAIN FAVORABLE, BUT UPPER-LEVEL OUTFLOW IS SOMEWHAT HINDERED BY A
TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL LOCATED TO THE
NORTHEAST, WHICH IS PROVIDING SOME PRESSURE AND SUBSIDENCE ON THE
NORTHERN SIDE OF THE SYSTEM. THE HINDERED OUTFLOW WILL LEAD TO SLOW
INTENSIFICATION THROUGH TAU 36 AS THE OUTFLOW REMAINS HINDER BY THE
PROXIMITY OF THE TUTT CELL. AFTER TAU 36 AS TD 20W MOVES OFF
TOWARDS THE WEST, THE UPPER LEVEL ENVIRONMENT WILL IMPROVE, WITH AN
UPPER-LEVEL ANTICYCLONE DEVELOPING OVER OR NEAR THE SYSTEM AROUND
TAU 48, ALLOWING FOR A PERIOD OF RAPID INTENSIFICATION AFTER TAU
48. AVAILABLE MODEL GUIDANCE IS IN GOOD AGREEMENT IN BOTH THE TRACK
AND SPEED THROUGH TAU 72.
C. IN THE EXTENDED FORECAST, TD 20W WILL CONTINUE TRACKING WEST-
NORTHWESTWARD TOWARDS SOUTHERN TAIWAN, UNDER THE STEERING INFLUENCE
OF THE DEEP LAYER STR. TD 20W WILL CONTINUE TO INTENSIFY IN THE
PHILIPPINE SEA, AS VWS REMAINS LOW, SSTS REMAIN OVER 30 DEG
CELSIUS. UPPER-LEVEL OUTFLOW WILL CONTINUE TO IMPROVE THROUGH THE
END OF THE FORECAST, WITH DUAL-CHANNEL OUTFLOW BECOMING ESTABLISHED
AROUND TAU 96, ALLOWING THE SYSTEM TO UNDERGO ANOTHER ROUND OF
RAPID INTENSIFICATION BETWEEN TAUS 72 AND 96, BEFORE REACHING A
PEAK INTENSITY OF 135 KNOTS BY TAU 120. ALTHOUGH THE MAJORITY OF
THE MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THIS SCENARIO, THE
NAVGEM MODEL DEPICTS A POTENTIAL ALTERNATE RECURVE SCENARIO, MOVING
THE TRACK TOWARDS THE VICINITY OF ISHIGAKI-JIMA BY TAU 120 IN
RESPONSE TO THE DEVELOPMENT OF A WEAKNESS IN THE STR. THE GFS MODEL
FIELDS ALSO DEPICT THE WEAKNESS IN THE STR, BUT THE MODEL TRACKERS
SHOW A TRACK FURTHER SOUTH AND DO NOT SHOW THE SYSTEM BEING
INFLUENCED BY THIS WEAKNESS. THERE IS OVERALL HIGH CONFIDENCE IN
THE JTWC FORECAST TRACK. THE INTENSITY GUIDANCE HOWEVER SHOWS A
SIGNIFICANT SPREAD, WITH COTC SHOWING LITTLE TO NO DEVELOPMENT
COMPARED TO HWRF AND CTCX, INDICATING RAPID INTENSIFICATION WITH A
PEAK NEAR 150 KNOTS. THE JTWC FORECAST IS SLIGHTLY LOWER THAN THE
HWRF SOLUTION THROUGH TAU 36, BUT THEN IN LINE WITH THIS SOLUTION
THROUGH TAU 120, AS THE DEPICTION OF THE OVERALL ENVIRONMENT IS
ASSESSED AS BEING THE MORE CORRECT SOLUTION. WITH SUCH A HIGH
DEGREE OF MODEL DISAGREEMENT, THERE IS LOW CONFIDENCE IN THE
INITIAL JTWC INTENSITY FORECAST.//
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