000
AXPZ20 KNHC 110331
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC FRI DEC 11 2009

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 
0300 UTC.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE IS ALONG THE LINE...06N77W TO 
07N98W TO 08N116W TO 07N130W TO 07N140W. A CLUSTER OF SCATTERED 
MODERATE CONVECTION IS NOTED NEAR 09N115W...AND NEAR 08N126W. 

...DISCUSSION... 

MARINE CONDITIONS W OF 110W ARE BEING DOMINATED BY LARGE AND 
LONG PERIOD NW SWELL...WITH WAVE PERIODS OF UP TO 20 SECONDS AND 
SIGNIFICANT WAVE HEIGHTS AS HIGH AS 18 FEET. THIS SWELL EVENT 
WILL CONTINUE TO PROPAGATE SE BEYOND THE EQUATOR OVER THE NEXT 
TWO DAYS. HOWEVER...THE SEA HEIGHTS ARE EXPECTED TO GRADUALLY 
SUBSIDE. A WEAKENING COLD FRONT EXTENDS FROM 30N124W TO 25N135W. 
A NARROW BAND OF MAINLY LOW CLOUDS WITH ISOLATED SHOWERS IS 
ASSOCIATED WITH THE FRONT. A BROAD UPPER-LEVEL TROUGH OVER THE 
EASTERN PACIFIC CENTERED OVER FORECAST WATERS ALONG 122W N OF 
15N SUPPORTS THE FRONT WHICH WILL CONTINUE TO DISSIPATE TONIGHT. 

AN UPPER-LEVEL ANTICYCLONE...CURRENTLY CENTERED OVER THE NW 
CARIBBEAN...EXTENDS A RIDGE ACROSS SE MEXICO AND NORTHERN 
CENTRAL AMERICA INTO THE EASTERN PACIFIC E OF 110W. STRONG UPPER 
LEVEL SUBSIDENCE AND IMPLIED DRY AIR MASS IS SEEN UNDER THE 
INFLUENCE OF THIS RIDGE. SLY WINDS BETWEEN THIS RIDGE AND THE 
AFOREMENTIONED BROAD UPPER-LEVEL TROUGH ARE TRANSPORTING 
ABUNDANT MID TO UPPER LEVEL MOISTURE FROM THE ITCZ TO THE N AND 
NE INTO NORTHERN MEXICO AROUND THE NW PORTION OF THE 
ANTICYCLONE. 

CONVECTION ALONG THE ITCZ HAS DIMINISHED SINCE YESTERDAY AS WELL 
AS ALONG THE SURFACE TROUGH EXTENDING FROM 19N120W TO 15N124W TO 
08N125W. THE LOW THAT WAS EMBEDDED ALONG THIS TROUGH HAS 
DISSIPATED. W OF THIS TROUGH...AN AREA OF ELY TRADE WINDS OF 20 
KT IS NOTED. THE TRADES ARE EXPECTED TO INCREASE TO 20-25 KT IN 
ABOUT 48 HOURS AS THE AFOREMENTIONED SFC TROUGH BECOMES 
DIFFUSE.  

THE NEXT COLD FRONT WILL ENTER THE FAR NW PORTION OF THE 
FORECAST REGION FRI AFTERNOON...WITH SW WINDS OF 20 TO 25 KT 
AHEAD OF THE FRONT. NW WINDS OF 20 KT AND SEAS OF UP TO 11 FT 
ARE EXPECTED IN THE WAKE OF THE FRONT. 

GAP WINDS...
WINDS ARE EXPECTED TO INCREASE TO 20 KT ONCE AGAIN BY EARLY FRI 
MORNING ACROSS THE GULF OF PAPAGAYO AS THE DRAINAGE FLOW OFF THE 
CENTRAL AMERICA LANDMASS INCREASES AND THE PRES GRADIENT BUILDS 
ACROSS THE WESTERN CARIBBEAN...ALLOWING EASTERLY TRADE WINDS TO 
FUNNEL ACROSS COSTA RICA AND NICARAGUA INTO THE EPAC. THIS GAP 
WIND EVENT WILL INCREASE IN SIZE WHILE SPREADING WWD BY SAT. 

THE NAM REGIONAL MODEL IS SHOWING N WINDS OF 20 KT ACROSS THE 
GULF OF TEHUANTEPEC BEGINNING FRI MORNING. THIS WEATHER PATTERN 
IS FORECAST TO PERSIST DURING THE NEXT 48 HOURS BUT PARTICULARLY 
BETWEEN 1200 AND 1800 UTC. 

$$
GR