WDPN33 PGTW 030300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (PARMA)WARNING NR 22// 
RMKS/
1. FOR METEOROLOGISTS. 
2. 12 HOUR SUMMARY AND ANALYSIS. 
    A. TYPHOON 19W (PARMA) LOCATED APPROXIMATELY 200 NM NORTH-
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 12 
KNOTS OVER THE PAST SIX HOURS. AS THE SYSTEM APPROACHES THE COAST OF 
LUZON, THE SYSTEM HAS SEEN A DISRUPTION IN THE CONVECTIVE BANDS 
ALONG THE WESTERN AND SOUTHWESTERN SIDES, AS SEEN IN RECENT ANIMATED 
INFRARED IMAGERY. THE SYSTEM REMAINS A TYPHOON, BUT THE INTENSITY 
HAS BEEN STEADILY DECREASING AS THE SYSTEM INTERACTS WITH LAND. 
INTENSITY IS BASED ON CURRENT INTENSITY ESTIMATES FROM PGTW AND 
RJTD. THE SYSTEM CONTINUES TO TRACK NORTHWESTWARD ON THE WESTERN 
PERIPHERY OF THE SUBTROPICAL RIDGE (STR) LOCATED TO THE EAST.
3. FORECAST REASONING 
    A. THE FORECAST REASONING HAS CHANGED SINCE THE LAST PROGNOSTIC 
REASONING BULLETIN. THE SYSTEM IS NOW EXPECTED TO TURN TOWARDS THE 
EAST AFTER TAU 48 IN RESPONSE TO A BUILDING RIDGE TO THE EAST AND 
DIRECT CYCLONE INTERACTION WITH TYPHOON 20W APPROACHING FROM THE 
EAST.
    B. TY 19W IS EXPECTED TO MAINTAIN A NORTHWESTWARD, ALBEIT
PROGRESSIVELY SLOWER, TRAJECTORY THROUGH TAU 24. DURING THIS PERIOD,
IT WILL GRADUALLY WEAKEN AS IT INTERACTS WITH THE EASTERN COAST OF 
LUZON. BY TAU 12, IT WILL CROSS BACK INTO THE LUZON STRAIT AND 
BECOME QUASI-STATIONARY IN A RELATIVELY WEAK STEERING ENVIRONMENT 
CREATED BY WEAKENING OF THE STR TO THE EAST. THE WEAK STEERING WILL 
PERSIST THROUGH TAU 48 BEFORE THE SYSTEM SLOWLY TURNS TO THE EAST 
AND ACCELERATES. THE AVAILABLE NUMERICAL MODEL GUIDANCE HAS GREATLY 
IMPROVED OVER THE LAST 12 HOURS WITH THE ALL AVAILABLE TRACKERS, 
WITH THE EXCEPTION OF JGSM, FAVORING A SCENARIO WITH A SHARP TURN TO 
THE EAST. SPEED AND TIMING OF THE TURN STILL VARY, BUT MOST MODELS 
COMPLETE A VERY SLOW CHANGE OF DIRECTION WITHIN THE LUZON STRAIT BY 
TAU 72 BEFORE MOVING OFF TOWARDS THE EAST.
    C. BEYOND TAU 72, TYPHOON PARMA WILL CONTINUE TO SLOWLY 
ACCELERATE TOWARDS THE EAST AS THE STR TO THE EAST SLOWLY BUILDS. AS 
TYPHOON 20W APPROACHES FROM THE EAST, WEAK INTERACTION IS EXPECTED 
TO HELP ACCELERATE 19W AND WILL STEER THE SYSTEM ON MORE OF AN 
EASTWARD TRACK, VICE AN EAST-NORTHEASTWARD TRACK AS WOULD BE 
EXPECTED BY THE STR STEERING INFLUENCE. MODEL GUIDANCE IS IN FAIR 
AGREEMENT AFTER TAU 72, WITH THE VARIATION LIKELY DUE TO DIFFERENT 
LEVELS OF INTERACTION WITH 20W. GFS, GFDN AND UKMO CALLING FOR A 
MORE EASTWARD TRACK AFTER TAU 72 AND ECMWF AND NOGAPS CALLING FOR 
STRONGER BINARY INTERACTION AND BRINGING 19W MORE EAST-SOUTHEASTWARD 
AFTER TAU 72. THIS FORECAST FAVORS THE MORE EASTWARD TRACK BECAUSE 
THE INTERACTION IN THE NOGAPS AND ECMWF MODELS HAS BEEN ANALYZED AS 
EXCESSIVE.//
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