000
AXPZ20 KNHC 132156
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC SUN DEC 13 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...05N77W TO 
07N90W TO 06N105W TO 07N125W TO 07N140W. SCATTERED MODERATE TO 
ISOLATED STRONG FROM 06N TO 09N W OF 125W.

...DISCUSSION...

A SHORTWAVE TROUGH IS OVER THE NW PORTION OF THE AREA MOVING 
EAST AT AROUND 25 KT AND WILL STRENGTHEN AS IT APPROACHES MEXICO 
MONDAY. OTHERWISE NEARLY ZONAL FLOW COVERS THE AREA N OF 20N. A 
JET STREAM BRANCH WITH CORE WINDS OF 70-95 KT ROUNDS THE BASE OF 
THE SHORTWAVE TROUGH ENTERING THE DISCUSSION AREA NEAR 23N140W.  
SOME MID/UPPER LEVEL MOISTURE IS NOTED ON WATER VAPOR IMAGERY N 
OF 25N WHILE MODERATE TO STRONG SUBSIDENCE WITH DRY STABLE AIR 
AT THE MIDDLE AND UPPER LEVELS OF THE ATMOSPHERE DOMINATES THE 
AREA N OF THE ITCZ W OF 105W.

AN UPPER ANTICYCLONE LOCATED OVER THE NW CARIBBEAN EXTENDS A  
RIDGE ACROSS SE MEXICO AND MOST OF CENTRAL AMERICA INTO THE EPAC 
WHERE IS PRODUCING MODERATE TO STRONG SUBSIDENCE MAINLY E OF 
100W. THE SUBSIDENCE HAS SUPPRESSED ANY STRONG CONVECTION ALONG 
THE ITCZ. 

A WEAKENING COLD FRONT IS MOVING ACROSS THE N WATERS EXTENDING 
FROM 30N116W TO 25N128W. THE FRONT WILL CONTINUE TO DISSIPATE 
DURING THE NEXT 12 TO 24 HOURS. A 1021 MB HIGH PRES NW OF THE 
FRONT IS CENTERED NEAR 29N134W. FRESH TO STRONG TRADE WINDS 
ON THE SOUTHERN PERIPHERY OF THIS HIGH ARE EVIDENT PER AN ASCAT 
PASS FROM AROUND 1835 UTC. THIS WEATHER PATTERN WILL PERSIST 
OVER THE NEXT COUPLE OF DAYS. THE NEXT COLD FRONT IS EXPECTED TO 
REACH THE FAR NW PORTION OF THE FORECAST REGION IN ABOUT 24 
HOURS. SW WINDS OF 20 KT WILL PRECEDE THE FRONT.  

A COUPLE OF TROUGH ARE ANALYZED ALONG THE ITCZ. THE FIRST TROUGH 
IS FROM 12N114W TO 05N116W. AN EARLIER ASCAT PASS SHOWED NE TO E 
WINDS OF 20 TO 25 KT EITHER SIDE OF THE TROUGH N OF 08N. A 
SECOND TROUGH RUNS FROM 11N132W TO 05N133W. MODERATE CONVECTION 
EITHER SIDE OF THE TROUGH AXIS IS 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 SUBSIDING 
ESPECIALLY OVER THE N PORTION OF THE AREA. A NEW BATCH OF NW 
SWELL WITH WAVE PERIODS BETWEEN 14 TO 15 SECONDS SHOULD REACH 
THE FAR NW PORTION OF THE AREA BY THIS EVENING.

WINDS IN THE GULF OF PAPAGAYO ARE EXPECTED TO OSCILLATE BETWEEN 
20 TO 25 KT OVER THE NEXT 48 HOURS AS A TIGHT PRES GRADIENT 
ACROSS THE WESTERN CARIBBEAN IS ALLOWING ELY TRADE WINDS TO 
FUNNEL ACROSS COSTA RICA AND NICARAGUA INTO THE EASTERN PACIFIC.

NLY WINDS OF 20 KT ARE STILL BLOWING ACROSS THE GULF OF 
TEHUANTEPEC. THE WINDS SHOULD DECREASE BY 36 HOURS...BUT ARE 
EXPECTED TO INCREASE AGAIN ABOUT MID WEEK.
  
$$
GR