000
AXPZ20 KNHC 180321
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC FRI SEP 18 2009

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

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0230 UTC.

...SPECIAL FEATURES...

AT 18/0300 UTC...TROPICAL STORM MARTY IS LOCATED NEAR 20.0N 
113.6W MOVING W-NW OR 325 DEG AT 3 KT. MAXIMUM SUSTAINED WIND 
SPEED IS 40 KT WITH GUSTS TO 50 KT. ESTIMATED MINIMUM CENTRAL 
PRESSURE IS 1002 MB. SEE LATEST NHC FORECAST/ADVISORY UNDER 
AWIPS/WMO HEADERS MIATCMEP1/WTPZ21KNHC FOR MORE DETAILS. 
MARTY IS FORECAST TO MOVE INTO A LESS FAVORABLE ENVIRONMENT 
CHARACTERIZED BY INCREASING SOUTHWESTERLY SHEAR AND A DRIER AND 
MORE STABLE AIRMASS. THIS SHOULD RESULT IN GRADUAL WEAKENING 
DURING THE NEXT DAY OR TWO...AND THE CYCLONE IS PREDICTED TO 
BECOME A REMNANT LOW IN ABOUT 48 HOURS.

AN AREA OF DISTURBED WEATHER LOCATED OFF OF THE SOUTHWEST COAST 
OF MEXICO ABOUT 150 MILES W-SW OF ZIHUATANEJO MEXICO IS BEING 
MONITORED FOR POSSIBLE TROPICAL DEVELOPMENT. DEEP CONVECTION HAS 
BEEN LINGERING ACROSS THIS GENERAL AREA FOR OVER 24 HOURS UNDER 
THE POSITIVE INFLUENCE OF DIFFLUENT FLOW ALOFT OCCURRING ON THE 
SOUTH SIDE OF UPPER RIDGING ACROSS THIS AREA. A LARGE CLUSTER OF 
DEEP CONVECTION BLOSSOMED LAST NIGHT AND MOVED AWAY FROM THE LOW 
LEVEL CENTER. AT 17/2100 UTC...VIS SATELLITE IMAGERY SHOWED A 
SMALL TIGHT LOW LEVEL CLOUD SWIRL EMERGING FROM THE WEAKENING 
CONVECTION NEAR 16.2N 103.1W. SINCE THEN...CONVECTION HAS BEGUN 
TO SLIGHTLY INCREASE NEAR THE CENTER OF CIRCULATION. ATMOSPHERIC 
AND OCEANIC CONDITIONS APPEAR FAVORABLE FOR FURTHER ORGANIZATION 
OF THIS SYSTEM OVER THE NEXT FEW DAYS AS IT MOVES IN A GENERAL 
NW DIRECTION...PARALLEL TO THE MEXICAN COAST AND TOWARD THE S 
END OF THE BAJA PENINSULA. THERE IS A MEDIUM CHANCE...30 TO 50 
PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE 
NEXT 48 HOURS.  

...TROPICAL WAVE...

A TROPICAL WAVE IS ANALYZED ALONG 131W MOVING W 15 KT. ONLY 
ISOLATED CONVECTION IS NOTED NEAR THE INTERSECTION OF THE WAVE 
AXIS AND THE ITCZ.  

A TROPICAL WAVE OVER THE WESTERN CARIBBEAN SEA WITH AXIS ALONG 
86W EXTENDS S INTO THE EPAC THROUGH NEAR THE COSTA RICA/ 
NICARAGUA BORDER. CONVECTION WITHIN THE ITCZ IS SEEN NEAR THIS 
WAVE AXIS.

...THE ITCZ...

THE INTERTROPICAL CONVERGENCE AXIS IS ALONG 10N87W TO 09N100W 
TO 13N128W TO 08N140W. SCATTERED MODERATE TO ISOLATED STRONG 
CONVECTION IS NEAR 07N87W AND NEAR 11N94W. SCATTERED MODERATE 
CONVECTION IS WITHIN 80 NM EITHER SIDE OF AXIS W OF 120W.

...DISCUSSION...

N OF 20N...A SURFACE RIDGE ANCHORED ON A HIGH PRES LOCATED NW OF 
AREA COVERS ROUGHLY THE REGION N OF 20N W OF 120W. THIS AREA IS 
MARKED BY MODERATE TO STRONG SUBSIDENCE AND BROKEN TO OVERCAST 
STRATOCUMULUS CLOUDS. THIS RIDGE IS PRODUCING TRADE WINDS OF 20 
KT AND SEAS 8 TO 9 FT BETWEEN 15N AND 20N W OF 128W. W TO NW 
SWELL CONTINUES TO INVADE THE NW WATERS RAISING SEAS INTO THE 8 
TO 10 FT RANGE. THESE MARINE CONDITIONS WILL PERSIST THROUGH FRI 
AS ANOTHER PULSE OF NLY WIND SWELL MOVES FROM OFFSHORE 
CALIFORNIA INTO THE AREA.

A DIFFLUENT PATTERN ALOFT ASSOCIATED WITH AN UPPER-LEVEL 
ANTICYCLONE EXTENDING FROM THE SRN GULF OF MEXICO TO W OF MARTY 
IS HELPING TO INDUCE AND SUSTAIN SEVERAL AREAS OF DEEP 
CONVECTION OVER THE EPAC WATERS S OF 20N AND E OF 110W.   

WAVE HEIGHTS ARE GENERALLY RUNNING AT 8 TO 9 FT OVER MUCH OF THE 
FORECAST AREA PRIMARILY IN NW SWELL. NEW PULSES OF S-SW LONG 
PERIOD SWELL WILL MOVE INTO THE WATERS DURING THE NEXT FEW DAYS. 

$$
GR/SS