000
AXPZ20 KNHC 121519
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SAT DEC 12 2009

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

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1500 UTC.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE IS ALONG THE LINE...06N77W TO 
06N105W TO 07N120W TO 07N140W. SCATTERED MODERATE CONVECTION IS 
WITHIN 60 NM OF THE POINT 07N120W. SCATTERED MODERATE TO STRONG 
CONVECTION IS WITHIN THE AREA FROM 06N TO 08.5N WEST OF 133W.

...DISCUSSION... 

MODERATE WESTERLIES ARE NORTH OF 20N. EMBEDDED SHORTWAVE IS OVER 
NORTHWEST MEXICO AND MOVING EAST 20 KNOTS AND WILL BE ABSORBED 
BY THE WESTERLIES OVER THE SOUTHERN UNITED STATES SUNDAY. NEXT 
SHORTWAVE WILL APPROACH THE NORTHWEST PART LATE SATURDAY AND BY 
MIDDAY SUNDAY BE ALONG ABOUT 132W NORTH OF 20N. NORTH OF 27N 
SCATTERED TO BROKEN MULTIPLE LEVEL CLOUDS ARE ASSOCIATED WITH 
THE MODERATE WESTERLIES. THE MOISTURE FOR THESE CLOUDS 
ORIGINATES FROM CONVECTION GENERATED BY A VIGOROUS SHORTWAVE 
LOCATED WELL WEST OF THE AREA JUST TO THE EAST OF THE DATELINE. 

AN UPPER LEVEL TROUGH EXTENDS FROM SOUTH TEXAS ACROSS NORTH 
CENTRAL MEXICO TO THE ITCZ NEAR 122W. A NARROW AND DIMINISHING 
BAND OF UPPER LEVEL MOISTURE IS WITHIN 150 NM EAST AND SOUTHEAST 
OF THE TROUGH. SOME HIGH CLOUDS ARE WITHIN THE BAND OVER MEXICO.

OTHERWISE A BROAD RIDGE IS OVER THE AREA IN THE MIDDLE AND UPPER 
LEVELS. DRY MIDDLE AND UPPER LEVELS ARE WEST OF THE UPPER TROUGH 
FROM 12N TO 24N IMPLYING STRONG SUBSIDENCE IN THIS AREA. DRY 
MIDDLE AND UPPER LEVELS ARE ALSO NOTED SOUTH OF THE ITCZ ACROSS 
THE ENTIRE AREA AND MOST OF THE AREA EAST OF THE NARROW BAND OF 
UPPER MOISTURE MENTIONED ABOVE. THE EXCEPTION IS SOME LOCAL ITCZ 
CONVECTION WHICH ARE INTRODUCING SOME MIDDLE AND UPPER LEVEL 
MOISTURE IN THE OTHERWISE DRY AREA.

AT THE SURFACE WEAKENING COLD FRONT EXTENDS THROUGH 32N128W TO 
26N140W. OTHERWISE A WEAK RIDGE IS NORTH OF 13N WEST OF 110W. 
ELSEWHERE A BROAD TROUGH CENTERED ALONG THE ITCZ IS ANALYZED AT 
THE SURFACE.

MARINE CONDITIONS W OF 105W ARE BEING DOMINATED BY LARGE AND 
LONG PERIOD NW SWELL...WITH WAVE PERIODS OF 12 TO 16 SECONDS AND 
SIGNIFICANT WAVE HEIGHTS AS HIGH AS 13 FT. THIS SWELL EVENT WILL 
CONTINUE TO PROPAGATE SE AND GRADUALLY SUBSIDE.

GAP NE TO E WINDS OF 20 TO 25 KT ACROSS THE GULF OF PAPAGAYO 
REGION AS TRADE WINDS CROSS CENTRAL AMERICA FROM THE WESTERN 
CARIBBEAN.
  
$$
LL