000
AXPZ20 KNHC 181535
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC FRI SEP 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 
1515 UTC.

...SPECIAL FEATURES...

AT 18/1500 UTC...TROPICAL STORM MARTY IS LOCATED NEAR 20.4N 
114.8W MOVING NW OR 305 DEG AT 6 KT. MAXIMUM SUSTAINED WIND 
SPEED REMAINS 35 KT WITH GUSTS TO 45 KT. ESTIMATED MINIMUM 
CENTRAL PRESSURE IS 1004 MB. A SMALL AREA OF NUMEROUS MODERATE 
TO STRONG CONVECTION DEVELOPED OVER AND NORTH OF THE CENTER 
EARLIER THIS MORNING...WITHIN 75 NM N AND 30 NM S 
SEMICIRCLES...BUT IT APPEARS TO HAVE WEAKENED SLIGHTLY OVER THE 
PAST HOUR OR TWO. 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. 

THE 1008 MB LOW PRESSURE SYSTEM IS CENTERED NEAR 17N106W...ABOUT 
140 NM SSW OF MANZANILLO MEXICO...MOVING WNW 5-10 KT. VISIBLE 
AND SHORTWAVE IR SATELLITE IMAGES SHOW A SMALL BUT FAIRLY WELL 
DEFINED MID-LEVEL CIRCULATION AND EARLIER ASCAT AND MICROWAVE 
DATA INDICATED THE PRESENCE OF A SURFACE CIRCULATION. 
CONVECTION REMAINS MINIMAL AND GENERALLY DISORGANIZED...THOUGH 
THERE IS A BURST WITHIN 120 NM E OF THE PARTIALLY EXPOSED 
CENTER. 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 ALONG 89W N OF 08N MOVING W 15 KT. SCATTERED 
MODERATE TO STRONG CONVECTION IS MAINLY LOCATED WEST OF THE AXIS 
OVER THE GULF OF TEHUANTEPEC FROM 13N-16N BETWEEN 93W-98W. THIS 
ACTIVITY IS LIKELY BEING ENHANCED BY A DIFFLUENT PATTERN ALOFT.

A TROPICAL WAVE IS ALONG 134W FROM 9N TO 15N MOVING W 15 KT. 
THIS WAVE IS ONLY PERTURBING THE ITCZ SLIGHTLY AND AIDING IN THE 
DEVELOPMENT OF SCATTERED MODERATE CONVECTION WITHIN THE 
INTERSECTION OF THE ITCZ...OUTLINED ABOVE.

...THE ITCZ...

INTERTROPICAL CONVERGENCE ZONE LIES ALONG A LINE FROM 11N86W TO 
11N91W TO 12N108W TO 13N132W TO 13N140W. SCATTERED MODERATE 
CONVECTION IS WITHIN 180 NM S OF AXIS BETWEEN 88W AND 100W. 
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 26N 
BETWEEN 121W-130W. SIMILAR MAGNITUDE NE TRADES EXIST ACROSS THE 
TROPICS BETWEEN THE ITCZ AND ABOUT 20N W OF 130W...STRONGEST 
NEAR THE TROPICAL WAVE. 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 
27N126W AND THEN CONTINUING WESTWARD TO 26N140W. ABUNDANT DRY 
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.

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