000
AXPZ20 KNHC 180951
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC FRI SEP 18 2009

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

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0230 UTC.

...SPECIAL FEATURES...

AT 18/0900 UTC...TROPICAL STORM MARTY IS LOCATED NEAR 20.4N 
114.3W MOVING NW OR 320 DEG AT 5 KT. MAXIMUM SUSTAINED WIND 
SPEED IS 35 KT WITH GUSTS TO 45 KT. ESTIMATED MINIMUM CENTRAL 
PRESSURE IS 1004 MB. SEE LATEST NHC FORECAST/ADVISORY UNDER 
AWIPS/WMO HEADERS MIATCMEP1/WTPZ21KNHC FOR MORE DETAILS. 
SCATTERED MODERATE CONVECTION CAN BE FOUND WITHIN 60 NM NW AND 
120 NM SE SEMICIRCLE OF TROPICAL STORM MARTY. MARTY IS MOVING 
INTO A LESS FAVORABLE ENVIRONMENT CHARACTERIZED BY INCREASING 
SOUTHWESTERLY SHEAR AND A DRIER AND MORE STABLE AIRMASS. THIS IS 
RESULTING IN GRADUAL WEAKENING THAT SHOULD CONTINUE DURING THE 
NEXT DAY OR TWO...AND THE CYCLONE IS PREDICTED TO BECOME A 
REMNANT LOW IN ABOUT 48 HOURS.

THE 1007 MB LOW PRES CENTER NEAR 17N104 W IS ASSOCIATED WITH AN 
AREA OF DISTURBED WEATHER LOCATED OFF OF THE SOUTHWEST COAST OF 
MEXICO. SCATTERED MODERATE CONVECTION CAN BE FOUND WITHIN 60 NM 
NW AND 120 NM SE SEMICIRCLE OF TROPICAL STORM MARTY. THE DEEP 
CONVECTION HERE LIES UNDER THE POSITIVE INFLUENCE OF DIFFLUENT 
FLOW ALOFT OCCURRING ON THE SOUTH SIDE OF UPPER RIDGING ACROSS 
THIS AREA. 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 132W FROM 10N TO 16N MOVING W 
15 KT. SCATTERED MODERATE CONVECTION CAN BE FOUND WITHIN 150 NM 
E OF WAVE AXIS FROM 12N TO 14N.

A TROPICAL WAVE IS ANALYZED ALONG 87W N OF 06N TO THE GULF OF 
FONSECA. SCATTERED MODERATE TO STRONG CONVECTION CAN BE FOUND 
WITHIN 150 NM OF COAST W OF WAVE AXIS TO 95W AND SCATTERED 
MODERATE CONVECTION CAN BE FOUND WITHIN 210 NM W OF AXIS FROM 
06N TO 08N.

...THE ITCZ...

INTERTROPICAL CONVERGENCE ZONE LIES ALONG A LINE FROM 12N88W TO 
11N107W TO 12N130W TO 10N137W TO 10N140W. ISOLATED MODERATE 
CONVECTION CAN BE FOUND WITHIN 90 NM EITHER SIDE OF THE ITCZ 
AXIS FROM 121W TO 126W.

...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 
TO 25 KT AND SEAS 8 TO 10 FT BETWEEN 15N AND 20N W OF 130W. W TO 
NW SWELL CONTINUES TO INVADE THE NW WATERS RAISING SEAS INTO THE 
8 TO 10 FT RANGE. THE PRES GRADIENT BETWEEN THE EASTERN SIDE OF 
THE RIDGE AND MEAN LOW PRES DUE TO MARTY AS WELL AS OVER THE 
GULF OF CALIFORNIA HAS INDUCED N WINDS INT HE 20 TO 25 KT RANGE 
N OF 27N FROM 122W TO 127W AS WELL. THESE CONDITIONS WILL SHIFT 
W AND DIMINISH SOMEWHAT OVER THE NEXT 48 HOURS.

A DIFFLUENT PATTERN ALOFT ASSOCIATED WITH AN UPPER-LEVEL 
ANTICYCLONE CENTERED OVER MEXICO NEAR 20N102W IS HELPING TO 
GENERATE NUMEROUS MODERATE CONVECTION WITHIN 90 NM OF THE 
MEXICAN COAST FROM 21N TO 23N.

WAVE HEIGHTS ARE GENERALLY RUNNING AT 8 TO 9 FT OVER MUCH OF THE 
FORECAST AREA PRIMARILY IN NW SWELL..BUT NEW PULSES OF S-SW LONG 
PERIOD SWELL ARE MOVING INTO SE WATERS AND WILL CONTINUE N TO 
THE COAST OF CENTRAL AMERICA OVER THE NEXT FEW DAYS. 

$$
SCHAUER CLARK