000
AXPZ20 KNHC 122143
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC SAT DEC 12 2009

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

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2100 UTC.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE IS ALONG THE LINE...06N80W TO 
07N106W TO 08N125W TO 07N140W. SCATTERED MODERATE TO ISOLATED 
STRONG CONVECTION IS FROM 06N TO 09N W OF 137W. SCATTERED 
MODERATE CONVECTION IS NOTED NEAR 07N123W.

...DISCUSSION... 

BROAD UPPER-LEVEL TROUGH WITH AXIS FROM NW MEXICO SW TO NEAR 
20N114W...OTHERWISE NEARLY ZONAL FLOW COVERS THE AREA N OF 20N W 
OF THE TROUGH. A 90-110 KT JETSTREAM IS JUST NORTH OF AREA 
CROSSING SOUTHERN CALIFORNIA...ARIZONA AND NEW MEXICO INTO 
TEXAS. SOME MID TO UPPER LEVEL MOISTURE IS N OF 23N WHILE STRONG 
SUBSIDENCE WITH DRY STABLE AIR AT THE MIDDLE AND UPPER LEVELS OF 
THE ATMOSPHERE DOMINATES THE AREA N OF THE ITCZ W OF 110W.

AN UPPER ANTICYCLONE OVER THE NW CARIBBEAN WITH RIDGE EXTENDING 
WWD OVER SE MEXICO AND MOST OF CENTRAL AMERICA INTO THE EPAC TO 
13N95W IS PRODUCING MODERATE TO STRONG SUBSIDENCE MAINLY E OF 
100W. THE SUBSIDENCE HAS SUPPRESSED ANY STRONG CONVECTION ALONG 
THE ITCZ. AN UPPER-LEVEL TROUGH IS IN THE DEEP TROPICS WITH AXIS 
FROM 12N100W TO A CYCLONIC CIRCULATION NEAR 04N98W.

A COLD FRONT IS MOVING ACROSS THE NW PORTION OF THE DISCUSSION 
AREA WITH SW WINDS 20 KT IN A SMALL AREA AHEAD OF THE FRONT 
WHICH EXTENDS FROM 30N128W TO 26N140W. THIS FRONTAL SYSTEM WILL 
MOVE RATHER QUICKLY ACROSS THE N WATERS AND BECOME DIFFUSE IN 
ABOUT 24 HOURS. E OF FRONT...A 1021 MB SURFACE HIGH IS CENTERED 
NEAR 26N118W. FRESH TO STRONG TRADE WINDS ON THE SOUTHERN 
PERIPHERY OF THIS HIGH ARE EVIDENT ON AN ASCAT PASS FROM AROUND 
1715 UTC AND SOME SHIP OBSERVATIONS. LITTLE CHANGE IS EXPECTED 
OVER THE NEXT 48 HOURS.

A COUPLE OF TROUGH ARE ANALYZED ALONG THE ITCZ. THE FIRST AND 
BETTER DEFINED EXTENDS FROM 11N106W TO A 1011 MB LOW PRES NEAR 
07N108W. AN EARLIER ASCAT PASS SHOWED SOME WIND SHIFT ASSOCIATED 
WITH THIS TROUGH. A WEAKER SECOND TROUGH GOES FROM 10N125W TO 
07N127W. A FEW SHOWERS NEAR THE TROUGH ARE MAINLY ASSOCIATED 
WITH THE ITCZ. 

LARGE AND LONG PERIOD NW SWELL CONTINUES TO SPREAD ACROSS THE 
REGION BEYOND THE EQUATOR. HOWEVER THE SEA HEIGHTS ARE BEGINNING 
TO SUBSIDE. A NEW BATCH OF NW SWELL WITH WAVE PERIODS BETWEEN 14 
TO 15 SECONDS SHOULD REACH THE FAR NW PORTION OF THE AREA BY SUN 
EVENING. THIS SWELL EVENT WILL BE ASSOCIATED WITH A STRONG 
EXTRATROPICAL CYCLONE MOVING ACROSS THE NE PACIFIC. 

GAP WINDS...
NE TO E WINDS OF 20 TO 25 KT ARE BLOWING ACROSS THE GULF OF 
PAPAGAYO AS THE PRES GRADIENT BUILDS ACROSS THE WESTERN 
CARIBBEAN...ALLOWING ELY TRADE WINDS TO FUNNEL ACROSS COSTA RICA 
AND NICARAGUA INTO THE EASTERN PACIFIC. 

NLY WINDS OF 20 KT ARE NOTED ACROSS THE GULF OF TEHUANTEPEC PER 
AN ASCAT PASS. COMPUTER GUIDANCE SUGGESTS THAT THIS WIND EVENT 
WILL PERSIST ACROSS THIS AREA OVER THE NEXT COUPLE OF DAYS.  
  
$$
GR