000
AXPZ20 KNHC 181552
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC WED NOV 18 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 CENTERED ALONG A LINE FROM 
09N83W TO 06N90W TO 08N100W TO 06N113W TO 09N128W TO 09N140W. 
SCATTERED MODERATE CONVECTION WITHIN 180 NM N OF AXIS W OF 125W.

...DISCUSSION...
W OF 115W...SCATTEROMETER PASSES OVER THE PAST 12 HOURS 
INDICATED 20 TO 30 KT NORTHERLY WINDS BEHIND A COLD FRONT THAT 
EXTENDS FROM 31N125W TO 27N140W 20N127W TO 27N138W. THE MAIN 
SHORT WAVE ENERGY SUPPORTING THIS FRONT IS PUSHING INTO THE 
CENTRAL CALIFORNIA COAST...ALLOWING THE FRONT TO STALL AND 
WEAKEN. THIS IN TURN WILL ALLOW WINDS TO DIMINISH N OF 25N W OF 
125W THROUGH TODAY. SURFACE HIGH PRES IS BUILDING IN BEHIND THE 
FRONT AND SHIFT E...CREATING A SQUEEZE WITH THE COAST THAT WILL 
ALLOW NORTHERLY WINDS TO INCREASE N OF 25N E OF 125W THROUGH 
TONIGHT. MEANWHILE LONG PERIOD NORTHERLY SWELL WITH HEIGHTS TO 
15 FT IS PUSHING INTO THE AREA BEHIND THE FRONT. FURTHER 
SOUTH...SCATTEROMETER DATA SHOW A LARGE SWATH OF FRESH TO STRONG 
TRADES WINDS PERSISTING FROM 08N TO 25N W OF 125W. THE WINDS 
WILL DIMINISH SLIGHTLY THROUGH LATE THU AS THE HIGH PRES N OF 
THE AREA WEAKENS AND SHIFTS EASTWARD...AHEAD OF ANOTHER COLD 
FRONT MOVING INTO THE NE PACIFIC. THE TRADE WIND CONVERGENCE IS 
ENHANCING SCATTERED MODERATE CONVECTION ALONG THE ITCZ W OF 
125W...WHICH WILL DIMINISH AS TRADE WIND FLOW DIMINISHES.

E OF 115W...HIGH RESOLUTION QUIKSCAT DATA FROM 12Z THIS MORNING 
SHOWS 35 TO 40 KT WINDS STILL ACTIVE THROUGH THE GULF OF 
TEHUANTEPEC. THE COOL AND DRY AIRMASS FILTERING THROUGH FROM THE 
GULF OF MEXICO THROUGH THE ITHMUS OF TEHUANTEPEC WILL SHIFT EAST 
AND MODERATE...ALLOWING THE GALES OVER THE GULF OF TEHUANTEPEC 
TO DIMINISH BELOW GALE STRENGTH BY THIS AFTEROON...WITH WINDS 
FURTHER DIMINISHING TO BELOW 20 KT BY THU AFTERNOON. FRESH NE TO 
E FLOW IS NOTED EMERGING SOME DISTANCE OUT OF THE TEHUANTEPEC 
AREA OFFSHORE TO AS FAR W AS 100W. ELSEWHERE LAND-BASED 
OBSERVATIONS THIS MORNING OVER THE HIGHER TERRAIN IN CENTRAL 
AMERICA CONFIRM WATER VAPOR IMAGERY ARE SHOWING THE COOL AND DRY 
AIRMASS IN PLACE. DECENT RADIATIONAL COOLING OVERNIGHT HAS 
ENHANCED DRAINAGE FLOW CONVERGENCE ALONG THE PACIFIC COASTS OF 
SOUTHERN MEXICO AND CENTRAL AMERICA. HIGH RESOLUTION QUIKSCAT IS 
ALSO SHOWING FRESH DRAINAGE WINDS THROUGH THE GULF OF 
FONSECA...AS WELL AS FRESH TO STRONG FLOW IN THE GULF OF 
PAPAGAYO. THIS FLOW WILL DIMINISH SOMEWHAT THROUGH TODAY...BUT 
EXPECT A REPEAT OVERNIGHT AT LEAST OVER PAPAGAYO. 

$$
CHRISTENSEN