000
AXPZ20 KNHC 182142
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC FRI DEC 18 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...07.5N78W 
TO 07N87W TO 05N101W TO 07N117W TO 07N140W. SCATTERED MODERATE 
ISOLATED STRONG CONVECTION WITHIN 120 NM EITHER SIDE OF AXIS E 
OF 100W. SCATTERED MODERATE ISOLATED STRONG CONVECTION WITHIN 
120 NM OF AXIS BETWEEN 112W AND 123W. NUMEROUS MODERATE 
SCATTERED STRONG CONVECTION WITHIN 100 NM EITHER SIDE OF AXIS W 
OF 126W.

...DISCUSSION...

WIDESPREAD CONVECTION WITHIN 100 NM OF ITCZ AXIS W OF 126W IS 
HELPING MAINTAIN UPPER LEVEL RIDGING ACROSS THE W PORTION OF THE 
FORECAST AREA. AN UPPER LEVEL TROUGH PREVAILS ACROSS THE CENTRAL 
PORTION OF THE FORECAST AREA. SCATTERED CONVECTION WITHIN 120 NM 
OF ITCZ AXIS E OF 100W IS HELPING MAINTAIN UPPER LEVEL RIDGING 
ACROSS THE E PORTION OF THE FORECAST AREA. SW FLOW TO THE E OF 
THE UPPER TROUGH IS ADVECTING MID AND UPPER LEVEL MOISTURE FROM 
THE ITCZ NEAR 119W TO THE YUCATAN PENINSULA. AN UPPER LEVEL LOW 
IS CENTERED NEAR 36.5N150W WITH TROUGHING EXTENDING  JUST W OF 
HAWAII. THE SW FLOW AHEAD OF THE UPPER TROUGH IS ADVECTING MID 
AND UPPER LEVEL MOISTURE ACROSS THE NW PORTION OF THE FORECAST 
AREA...N OF 17N AND W OF 130W. 

AT THE SURFACE...HIGH PRESSURE 1025 MB CENTERED JUST NORTH OF 
THE FORECAST AREA NEAR 30.5N130W. THE PRESSURE GRADIENT BETWEEN 
THIS FEATURE...AND THE RELATIVELY LOWER PRESSURE IN THE ITCZ 
RESULTING FROM THE ABUNDANT CONVECTION W OF 126W IS MAINTAINING 
FRESH TO STRONG TRADES FROM 07N TO 19N W OF 116W. THIS HIGH 
PRESSURE WILL WEAKEN THROUGH THE WEEKEND AS THE UPPER LEVEL LOW 
MENTIONED IN THE PREVIOUS PARAGRAPH SHIFTS EASTWARD. AS A 
RESULT...THE AREAL COVERAGE OF THE FRESH TO STRONG TRADEWINDS 
ACROSS THE W PORTION OF THE AREA WILL DECREASE. A COLD FRONT 
WILL SHIFT INTO THE FAR NW PORTION OF THE FORECAST AREA SAT. THE 
FRONT HAS GENERATED A SET OF LONG PERIOD NW SWELLS WHICH WILL 
SPREAD INTO THE NW PORTION OF THE FORECAST AREA ON SATURDAY. 
LOW PRESSURE 1009 MB IS CENTERED NEAR 06N116W. THE LOW IS 
FORECAST TO DRIFT SLOWLY TO THE N. 

GAP WINDS...THE GALE WARNING FOR GULF OF TEHUANTEPEC HAS EXPIRED 
THIS AFTERNOON AS WINDS HAVE FALLEN TO 20 TO 25 KT...WHICH IS 
EXPECTED TO CONTINUE THROUGH AT LEAST MONDAY.

THE COMBINATION OF STRONG TRADE WINDS IN THE CARIBBEAN AND LOCAL 
DRAINAGE EFFECTS WILL ALLOW THE FRESH WINDS TO PERSIST THROUGH 
THE GULF OF PAPAGAYO ALSO THROUGH AT LEAST MONDAY.

FOR ADDITIONAL INFORMATION PLEASE VISIT 
HTTP://WWW.HURRICANES.GOV/MARINE
  
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AL