000
AXPZ20 KNHC 111515
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC FRI DEC 11 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...05N77W TO 
07N110W TO 07N140W. THERE IS NO SIGNIFICANT CONVECTION ALONG THE 
ITCZ.

...DISCUSSION... 

MODERATE WESTERLIES ARE NORTH OF 20N. EMBEDDED SHORTWAVE EXTENDS 
FROM SOUTHERN CALIFORNIA/NORTHERN BAJA CALIFORNIA SOUTHWEST TO 
NEAR 20N122W. SHORTWAVE IS MOVING EAST 20 KNOTS AND WILL BE OVER 
NORTHERN MEXICO SATURDAY THEN 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 130W NORTH OF 20N. 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 THE BIG BEND REGION OF TEXAS 
ACROSS NORTHERN MEXICO TO THE SOUTHERN TIP OF BAJA CALIFORNIA TO 
THE ITCZ NEAR 130W. A NARROW AND DIMINISHING BAND OF UPPER LEVEL 
MOISTURE AND BROKEN TO OVERCAST CLOUDS IS WITHIN 200 NM EAST AND 
SOUTHEAST OF THE TROUGH. 

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 13N TO 22N 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 FROM 100W TO 102W AND ALSO EAST OF 86W. BOTH OF 
THESE CONVECTION AREAS ARE INTRODUCING SOME MIDDLE AND UPPER 
LEVEL MOISTURE IN THE OTHERWISE DRY AREA.

AT THE SURFACE A WEAK RIDGE IS NORTH OF 15N WEST OF 112W. 
ELSEWHERE A BROAD TROUGH CENTERED ALONG THE ITCZ IS ANALYZED AT 
THE SURFACE.

MARINE CONDITIONS W OF 110W ARE BEING DOMINATED BY LARGE AND 
LONG PERIOD NW SWELL...WITH WAVE PERIODS OF 12 TO 18 SECONDS AND 
SIGNIFICANT WAVE HEIGHTS AS HIGH AS 15 FT. THIS SWELL EVENT WILL 
CONTINUE TO PROPAGATE SE BEYOND THE EQUATOR OVER THE NEXT TWO 
DAYS. THESE SEA HEIGHTS ARE EXPECTED TO GRADUALLY SUBSIDE.

THE NEXT COLD FRONT WILL ENTER THE FAR NW PORTION OF THE 
FORECAST REGION THIS AFTERNOON WITH SW WINDS OF 20 TO 25 KT IN A 
SMALL AREA AHEAD OF THE FRONT.

WINDS ARE HAVE INCREASED TO 20 KT ACROSS THE GULF OF PAPAGAYO AS 
THE GAP WINDS ACROSS THE CENTRAL AMERICA INCREASE AND THE PRES 
GRADIENT BUILDS ACROSS THE WESTERN CARIBBEAN...ALLOWING EASTERLY 
TRADE WINDS TO FUNNEL ACROSS COSTA RICA AND NICARAGUA INTO THE 
EPAC.

$$
LL