000
AXPZ20 KNHC 182124
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC FRI SEP 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 
2115 UTC.

...SPECIAL FEATURES...

AT 18/2100 UTC...TROPICAL STORM MARTY IS LOCATED NEAR 21.1N 
115.2W MOVING NW OR 310 DEG AT 6 KT. MAXIMUM SUSTAINED WIND 
SPEED REMAINS 35 KT WITH GUSTS TO 45 KT. ESTIMATED MINIMUM 
CENTRAL PRESSURE IS 1004 MB. MUCH OF THE DEEP CONVECTION HAS 
DIMINISHED OVER THE PAST FEW HOURS...AND THE SMALL AREA OF DEEP 
CLOUDINESS REMAINING IS BEING SHEARED BY STRONG SOUTHWESTERLY 
FLOW ALOFT. MARTY IS FORECAST TO DEGENERATE INTO A REMNANT LOW 
WITHIN THE NEXT 36 HOURS AS IT ENCOUNTERS STRONGER VERTICAL WIND 
SHEAR... DRIER AIR...AND COOLER WATERS. SEE LATEST NHC 
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP1/WTPZ21KNHC 
FOR MORE DETAILS. 

A 1008 MB LOW PRESSURE SYSTEM IS CENTERED NEAR 18N106W...ABOUT 
150 NM SW OF MANZANILLO MEXICO...MOVING WNW 5-10 KT. VISIBLE  
SATELLITE IMAGES SHOW A SMALL BUT FAIRLY WELL DEFINED LOW TO 
MID-LEVEL CIRCULATION AND EARLIER ASCAT AND MICROWAVE DATA 
INDICATED THE PRESENCE OF A SURFACE CIRCULATION. CONVECTION HAS 
ALSO INCREASED IN INTENSITY AND COVERAGE NEAR THE CENTER BUT IS 
STILL OVER A RATHER SMALL AREA FROM 16N-18N BETWEEN 106-107W. 
THERE IS A HIGH CHANCE...GREATER THAN 50 PERCENT...OF THIS 
SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

...TROPICAL WAVE...

A TROPICAL WAVE IS ALONG 90W N OF 09N MOVING W 15 KT. SCATTERED 
MODERATE TO STRONG CONVECTION IS MAINLY LOCATED WEST OF THE AXIS 
NEAR THE GULF OF TEHUANTEPEC FROM 11N-16N BETWEEN 94W-100W. THIS 
ACTIVITY IS LIKELY BEING ENHANCED BY A DIFFLUENT PATTERN ALOFT.

...THE ITCZ...

INTERTROPICAL CONVERGENCE ZONE LIES ALONG A LINE 10N86W TO 
11N92W TO 10N100W TO 12N110W TO 12N130W TO 11N140W. SCATTERED 
MODERATE ISOLATED STRONG CONVECTION IS WITHIN 180 NM S OF THE 
AXIS BETWEEN 88W AND 107W. SCATTERED MODERATE ISOLATED STRONG 
CONVECTION IS FROM 10N TO 13N BETWEEN 124W AND 131W.

...DISCUSSION...

W OF 110W...HIGH PRESSURE RIDGING HAS SET UP ALONG 32N/33N SOUTH 
OF A WELL DEFINED COLD FRONT. THE PRESSURE GRADIENT BETWEEN THE 
RIDGE AND LOWER PRESSURE OVER THE SOUTHWESTERN UNITED STATES AND 
NORTHWESTERN MEXICO IS PRODUCING NLY 20 KT WINDS N OF 28N 
BETWEEN 121W-131W. SIMILAR OR SLIGHTLY STRONGER NE TRADES EXIST 
ACROSS THE TROPICS BETWEEN THE ITCZ AND ABOUT 20N W OF 130W. 
BOTH OF THESE AREAS ARE EXPECTED TO DIMINISH OVER THE NEXT 
COUPLE OF DAYS AS THE SURFACE RIDGE SHIFTS NE. 

IN THE MID AND UPPER LEVELS...HIGHLY ELONGATED TROUGHING EXTENDS 
FROM THE ARIZONA/MEXICO BORDER SOUTHWESTWARD TO A LOW NEAR 
26N126W AND THEN CONTINUING WESTWARD TO 26N140W. ABUNDANT DRY 
STABLE AIR EXISTS...ESPECIALLY IN THE UPPER CONFLUENT AREA TO 
THE W OF TROPICAL STORM MARTY.

E OF 110W...A MID TO UPPER HIGH IS CENTERED OVER SOUTHERN 
MEXICO. A DIFFLUENT PATTERN ON THE SE PERIPHERY OF THE HIGH IS 
AIDING IN THE DEVELOPMENT OF CONVECTION OVER THE GULF OF 
TEHUANTEPEC. OTHERWISE...CONVECTION IS CONFINED TO THE ITCZ AND 
LOW NEAR 18N106W.

SW SWELL OF 14-16 SECONDS HAS REACHED THE PACIFIC COASTS OF 
MEXICO AND CENTRAL AMERICA. WAVE WATCH GUIDANCE SHOWS A NEW SLY 
SWELL TRAIN WITH LEADING PERIODS OF 17-19 SECONDS REACHING THE 
COASTLINE BY SUN.

$$
CANGIALOSI