000
AXPZ20 KNHC 190333
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC SAT SEP 19 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 
0300 UTC.

...SPECIAL FEATURES...

AT 19/0300 UTC...TROPICAL STORM MARTY IS LOCATED NEAR 21.9N 
115.9W MOVING NW OR 315 DEG AT 8 KT. MAXIMUM SUSTAINED WIND 
SPEED IS NOW 30 KT WITH GUSTS TO 40 KT. ESTIMATED MINIMUM 
CENTRAL PRESSURE IS 1004 MB. SATELLITE IMAGERY INDICATES THAT 
MARTY HAS BECOME A SWIRL OF LOW-TO MID-LEVEL CLOUDS...WITH 
INTERMITTENT BURSTS OF DEEP CONVECTION LIMITED TO A SMALL AREA 
NORTHEAST OF THE CENTER. THE CYCLONE 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 1006 MB LOW PRESSURE SYSTEM IS CENTERED NEAR 18N107W...ABOUT 
190 MILES WEST-SOUTHWEST OF MANZANILLO...MOVING W-NW TO NW NEAR 
10 KT. 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 MAINLY IN ABOUT 100 NM 
WIDE BAND EXTENDING FROM 16N106W TO 19N108W. ENVIRONMENTAL 
CONDITIONS APPEAR FAVORABLE FOR ADDITIONAL DEVELOPMENT...AND A 
TROPICAL DEPRESSION COULD FORM AT ANY TIME DURING NEXT DAY OR 
TWO. 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 91W N OF 09N MOVING W 15 KT. THE WAVE 
IS ENHANCING CONVECTION OVER SE MEXICO AND THE YUCATAN PENINSULA 
WITH A CLUSTER OF MODERATE TO ISOLATED STRONG CONVECTION ALONG 
THE COASTLINE NEAR 15N93W. ALL THIS ACTIVITY IS LIKELY BEING 
ENHANCED BY A DIFFLUENT PATTERN ALOFT.

...THE ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE LIES ALONG 08N78W TO 09N105W 
TO 11N125W TO 10N140W. SCATTERED MODERATE ISOLATED STRONG IS 
WITHIN 130 NM EITHER SIDE OF AXIS BETWEEN 94W AND 108W. 
SCATTERED MODERATE ISOLATED STRONG IS FROM 09N TO 13N W OF 118W.

...DISCUSSION...

HIGH PRESSURE RIDGING DOMINATES THE NW PORTION OF THE AREA 
MAINLY N OF 20N AND W OF 120W. WINDS AND SEAS HAS DIMINISHED 
ACROSS MUCH OF THE AREA COMPARED WITH THE PREVIOUS DAYS. 
HOWEVER...NW SWELL CONTINUES TO ROUGHLY AFFECT THE REGION N OF 
10N AND W OF 120W KEEPING SEAS IN THE 8 TO 10 FT RANGE. NE TRADE 
WINDS OF 15 TO 20 KT EXIST ACROSS THE TROPICS BETWEEN THE ITCZ 
AND ABOUT 20N W OF 130W. THESE CONDITIONS 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 26N140W. THE 
AREA N OF 15N AND W OF MARTY IS MARKED BY MODERATE TO STRONG 
SUBSIDENCE AND THE IMPLIED DRY AIR MASS. ONLY BROKEN 
STRATOCUMULUS CLOUDS ARE NOTED.

E OF 110W...A MID TO UPPER HIGH IS CENTERED OVER SOUTH-CENTRAL 
MEXICO. A DIFFLUENT PATTERN ON THE SE PERIPHERY OF THE HIGH IS 
AIDING IN THE DEVELOPMENT OF CONVECTION OVER SE MEXICO AND ALONG 
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.

$$
GR/JC