000
AXPZ20 KNHC 190400
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC FRI DEC 19 2008

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN
FROM THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0330 UTC.

...ITCZ...

INTERTROPICAL CONVERGENCE ZONE IS CENTERED ALONG...5N78W 6N90W
6N100W 7N110W 8N120W 6N130W 5N140W. SCATTERED MODERATE CONVECTION
IS WITHIN 120 NM N OF THE AXIS BETWEEN 111W-114W AND ALSO BETWEEN
120W-122W.

...DISCUSSION...

UPPER LEVEL PATTERN IS CHARACTERIZED BY AN OMEGA BLOCK FROM THE 
CENTRAL PACIFIC TO WESTERN N AMERICA...WITH A HIGHLY AMPLIFIED 
UPPER RIDGE W OF THE AREA 150W...A LONGWAVE UPPER TROUGH FROM 
THE ROCKIES SW INTO THE AREA THROUGH 32N127W TO 24N133W TO THE
DEEP TROPICS TO WEAK UPPER LEVEL LOW NEAR 11N131W. TO THE E OF
THE TROUGH...MID/UPPER LEVEL RIDGING EXTENDS FROM THE WESTERN 
GULF OF MEXICO WSW ALONG 20N103W TO NEAR 15N116W. A DECAYING
SURFACE COLD FRONT ASSOCIATED WITH THE LONGWAVE TROUGH EXTENDS 
FROM NW MEXICO SW TO JUST S OF BAJA CALIFORNIA. BEHIND THE FRONT 
NW-N WINDS TO 20 KT ARE PRESENTLY OCCURRING...BUT ARE FORECAST 
TO BECOME N-NE AND INCREASE TO 20-25 KT N OF 18N BETWEEN 
117W-127W AS HIGH PRES TO THE N STRENGTHENS. MAIN MARINE IMPACT 
WILL CONTINUE TO BE NLY SWELLS UP TO 11 FT THAT ARE TRAINING SWD 
BEHIND THE FRONT TOWARDS THE EQUATORIAL ZONE. WAVEWATCH GUIDANCE 
SUGGESTS THAT THESE SWELLS WILL SLOWLY DECAY THROUGH THE NEXT 
24-30 HOURS AS ANOTHER COLD FRONT NOW ENTERING THE NW CORNER OF 
THE AREA QUICKLY PUSHES TO ALONG 30N135W TO 26N140W IN 24 HOURS 
THEN LOSES ITS IDENTITY IN 48 HOURS. SW WINDS OF 20 KT AHEAD OF 
THE FRONT ARE EXPECTED TO DIMINISH IN 24 HOURS...WHILE WAVEWATCH
GUIDANCE SHOWS SEAS ONLY BUILDING TO ABOUT 7 OR 8 FT THROUGH 
TONIGHT BEFORE SUBSIDING TO 6 OR 7 FT FRI NIGHT OR EARLIER.

STRONG S TO SW FLOW ALOFT GENERALLY BETWEEN 110W AND 130W 
STREAMING FROM THE ITCZ NE TOWARDS BAJA CALIFORNIA AND NORTHERN 
MEXICO CONTINUES TO SUPPORT A FAVORABLE UPPER LEVEL ENVIRONMENT 
ENHANCING CONVECTION WITHIN THIS AREA WHERE CIMSS TPW LOOPS SHOW 
AMPLE MOISTURE CONVERGING DUE TO PROGRESSIVE EASTERLY FLOW IN 
THE TROPICAL EPAC...AND NORTHERLY FORCING FROM THE COLD FRONTAL 
ZONE INTRUDING S INTO THE SUBTROPICS. CONVECTION IS LIKELY TO 
PERSIST DURING THE NEXT 24 HOURS THERE AS ANOTHER WEAK EASTERLY 
WAVE ALONG 118W CONTRIBUTES IN MAINTAINING BROAD LOW LEVEL 
CONVERGENCE. IN FACT...GFS GUIDANCE CONTINUES TO SUGGEST THE 
DEVELOPMENT OF A BROAD LOW LEVEL TROUGH OR EVEN SURFACE LOW 
BETWEEN 118W AND 125W DURING THE NEXT 2 TO 3 DAYS. THIS IS MOST 
PROBABLY DUE TO OCCUR IN RESPONSE TO SHORT WAVE ENERGY ACROSS 
THE CENTRAL PACIFIC DIVING INTO THE BACKSIDE OF THE LONGWAVE 
UPPER TROUGH AND DEVELOPING AN UPPER CUT-OFF LOW NEAR 23N132W BY 
24 HOURS. MODELS THEN RETROGRADE THE LOW SW TO NEAR 20N134W BY 
48 HOURS. THIS SCENARIO WILL SUPPORT ACTIVE ITCZ CONVECTION 
MAINLY TO BETWEEN 110W AND 130W THROUGH SAT WITH THE NORTHERN 
EDGE OF THE CONVECTION BEING ADVECTED NE ACROSS THE EPAC WARM 
SST RIDGE TO NEAR THE SOUTHERN TIP OF BAJA CALIFORNIA.   

NE TRADES OF 20-25 KT CONTINUE ACROSS THE W CENTRAL SECTION OF 
THE AREA FROM 9N-21N W OF 119W AS VERIFIED BY QUIKSCAT DATA
FROM NEAR 1400 UTC THIS MORNING. THIS AREA IS FORECAST TO MERGE 
WITH THE AREA OF N-NE WINDS OF 20-25 KT N OF 18N BETWEEN 
117W-127W IN THE NEXT 48 HOURS IN RESPONSE TO A TIGHTENING 
PRESSURE GRADIENT DUE TO HIGH PRES N OF THE AREA BRIEFLY 
STRENGTHENING. PATCHES OF MOSTLY STRATOCUMULUS CLOUDS MOVING
WSW IN THE TRADE WIND FLOW WITH POSSIBLE ISOLATED SHOWERS ARE 
NOTED ACROSS THIS PORTION OF THE AREA.

GAP WINDS...
N-NE WINDS OF 20-25 KT THROUGH THE GULF OF TEHUANTEPEC AND 
PAPAGAYO ARE EXPECTED TO DIMINISH TO 20 KT IN ABOUT 24 HOURS 
THROUGH THE GULF OF TEHUANTEPEC AND TO LESS THAN 20 KT IN 36 
HOURS THERE. OVER THE GULF OF PAPAGAYO...THESE WINDS ARE 
EXPECTED TO DIMINISH TO LESS THAN 20 KT IN 48 HOURS. A FEW 
PATCHES OF BROKEN TO OVERCAST LOW AND MID CLOUDS WITH POSSIBLE 
ISOLATED SHOWERS ARE MOVING SW FROM THE WESTERN CARIBBEAN ACROSS 
COSTA RICA IN THE NE FLOW. NE WINDS TO 20 KT IN THE GULF OF 
PANAMA ARE FORECAST TO DROP BELOW 20 KT IN ABOUT 24 HOURS.

$$
AGUIRRE