000
AXPZ20 KNHC 200917
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC TUE DEC 20 2011

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS 
BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND 
METEOROLOGICAL ANALYSIS.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0700 UTC.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
THE MONSOON TROUGH AXIS EXTENDS FROM 09N83W TO 08N91W. THE ITCZ 
AXIS EXTENDS FROM 08N91W TO 09N107W TO 07N114W TO 10N132W TO 
09N140W. SCATTERED MODERATE CONVECTION IS WITHIN 180 NM N AND 75 
NM S OF THE AXIS W OF 130W. ISOLATED MODERATE CONVECTION IS 
WITHIN 45 NM EITHER SIDE OF THE AXIS BETWEEN 100W AND 127W.

...DISCUSSION...

THE UPPER PATTERN FEATURES A MEAN TROUGH OVER NW MEXICO THAT IS 
BEING RELOADED WITH NORTHERN STREAM ENERGY CURRENTLY OVER 
SOUTHERN CALIFORNIA AND A RIDGE EXTENDING INTO THE NW CORNER OF 
THE FORECAST AREA NEAR 31N140W FROM AN ANTICYCLONE CURRENTLY 
LOCATED NEAR 11N107W. THIS ANTICYCLONE WILL DRIFT E ABOUT 10 
DEGREES OVER THE NEXT FEW DAYS. RIDGING AT THE SURFACE LIES OVER 
MUCH OF THE NORTHERN HALF OF THE FORECAST AREA STEMMING FROM 
1035 MB HIGH PRES NEAR 40N136W. THE PRES GRADIENT BETWEEN THIS 
RIDGING AND TROUGHING ALONG THE ITCZ IS INDUCING A LARGE SWATH 
OF FRESH TRADE WINDS THAT EXTENDS AS FAR E AS 105W. THESE TRADE 
WINDS WILL SHRINK W ABOUT 10 DEGREES BY EARLY WED AS THE MEAN 
TROUGHING OVER NW MEXICO RELOADS AND IMPINGES ON THE RIDGE OVER 
NE WATERS. 

ISOLATED MODERATE CONVECTION LIES ALONG THE ITCZ OVER CENTRAL 
WATERS. THIS CONVECTION IS ENHANCED BY THE UPPER LEVEL 
DIFFLUENCE ASSOCIATED WITH THE AFOREMENTIONED ANTICYCLONE. THE 
CONVECTION IS DESCRIBED IN THE ITCZ/MONSOON TROUGH SECTION 
ABOVE. FARTHER W...A SURFACE TROUGH LIES FROM 14N130W TO 
08N133W. PRECIPITABLE WATER IMAGERY SHOWS LOW LEVEL MOISTURE 
POOLING NEAR THIS TROUGH AND SUPPLYING FUEL FOR THE SCATTERED 
MODERATE CONVECTION ALONG THE ITCZ FOUND W OF 130W. 

GAP WINDS...
GULF OF PAPAGAYO...THE 0328 UTC ASCAT PASS CAPTURED 20 KT NE-E 
WINDS DOWNWIND OF THE GULF OF PAPAGAYO. WINDS HERE HAVE 
DIMINISHED SLIGHTLY SINCE MON AS HIGH PRES TO THE HAS N SHIFTED 
EASTWARD OFF THE SE U.S. COAST...LESSENING THE PRES GRADIENT 
ACROSS CENTRAL AMERICA. THE HIGH IS NOW EXPECTED TO MOVE VERY 
SLOWLY EASTWARD OVER THE NEXT FEW DAYS...ALLOWING THE GRADIENT 
TO REMAIN STRONG ENOUGH TO SUPPORT FRESH GAP FLOW HERE THROUGH 
THE END OF THE PERIOD THU MORNING. WINDS WILL BE STRONGEST IN 
THE EARLY MORNING HOURS WITH THE ASSISTANCE OF DRAINAGE FLOW OFF 
THE LAND.
 
$$
SCHAUER