000
AXPZ20 KNHC 131557
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SUN SEP 13 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 
1500 UTC.

...TROPICAL WAVES...

TROPICAL WAVE WAS ANALYZED ALONG 93W FROM 06-19N MOVING W 15 
KT. 

TROPICAL WAVE WAS ANALYZED ALONG 111W/112W FROM 05-17N MOVING W 
15 KT. 

...THE ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE WAS ANALYZED ALONG THE LINE 
09N79W TO 08N83W TO 09N87W TO 15N94W TO 14N107W TO 08N115W TO 
07N199W TO 07N140W. CONVECTION E OF 90W HAS DIMINISHED 
CONSIDERABLY IN THE PAST 24-36 HOURS...WITH ONLY ISOLATED 
MODERATE TO STRONG CONVECTION NOTED WITHIN 120 NM EITHER SIDE OF 
AXIS THERE. SCATTERED MODERATE TO STRONG CONVECTION WAS 
OCCURRING N OF 06N TO JUST OFFSHORE OF THE MEXICAN COAST BETWEEN 
92W AND 113W...ATTRIBUTED MORE TO A BROAD MONSOONAL LIKE 
CIRCULATION THAN TO THE ITCZ FORCING. ISOLATED CLUSTERS OF 
MODERATE TO STRONG CONVECTION WHERE WITHIN 120 NM EITHER SIDE OF 
AXIS W OF 120W.

...DISCUSSION...

DEEP LAYER TROUGH IS OVER THE NORTHWEST PART OF THE AREA 
NORTHWEST OF A LINE FROM SOUTHERN CALIFORNIA TO 22N140W. THE 
AREA IS DRY AND CLOUD FREE IN THE MIDDLE AND UPPER LEVELS WITH 
BROKEN TO OVERCAST STRATOCUMULUS IN THE LOWER LEVELS. A WEAK 
COLD FRONT IS OVER THE FAR NORTHWEST PART OF THE AREA. THE 
TROUGH IS FORECAST TO MOVE EAST AND BE REPLACED BY NEAR ZONAL 
FLOW IN THE NEXT DAY OR TWO. THE COLD FRONT IS FORECAST TO 
WEAKEN AS IT MOVES EAST BECOMING DIFFUSE SOUTH OF 32N MONDAY. 
LONG PERIOD NWLY SWELLS GENERATED BEHIND THIS FRONT HAVE ALREADY 
PROPAGATED INTO NW PORTIONS OF THE AREA AND HAVE REACHED ALONG A 
LINE ROUGHLY FROM CENTRAL BAJA CALIFORNIA TO THE EQUATOR ALONG 
145W. THIS PULSE OF NW SWELL WILL CONTINUE SE ACROSS THE AREA 
TODAY AND TONIGHT...ALLOWING FOR SEAS TO PEAK AT AROUND 9 FT 
ACROSS THE NW HALF OF THE AREA...AND 10 OF 11 FT IN THE VICINITY 
OF THE REMNANTS OF LINDA NEAR 21N133W...WHERE NELY WIND WAVES 
ARE MIXING WITH THIS LONG PERIOD NW SWELL. A STRONGER COLD 
FRONT...PRESENTLY WELL NW OF THE AREA...IS FORECAST TO MOVE INTO 
THE FAR NW PORTION OF THE AREA LATE MON NIGHT INTO TUE PRECEDED 
BY INCREASING SLY WINDS AND BUILDING SEAS. 

ANOTHER DEEP LAYER TROUGH EXTENDS SOUTH FROM A CYCLONIC 
CIRCULATION THAT IS OVER TEXAS. THE TROUGH IS EAST OF A LINE 
THAT EXTENDS FROM SOUTHEASTERN ARIZONA TO THE ITCZ NEAR 100W AND 
WEST OF A LINE THAT EXTENDS FROM SOUTHEASTERN LOUISIANA TO THE 
ITCZ NEAR 95W. SCATTERED MODERATE TO STRONG CONVECTION IS IN THE 
ITCZ NEAR THE BASE OF THE TROUGH. CONVECTION OVER THE SIERRA 
MADRE OCCIDENTAL DURING THE DAY TODAY IS LIKELY DUE TO LINGER 
MOISTURE AND INSTABILITY OF THIS TROUGH.

BETWEEN THE TWO ABOVE TROUGHS A LARGE BROAD ANTICYCLONIC 
CIRCULATION DOMINATES THE FLOW. DIFFLUENT FLOW ALOFT ALONG THE 
SOUTHEASTERN PART OF THIS RIDGE IS ACTING TO VENTILATE 
CONVECTION ASSOCIATED WITH THE MONSOONAL CIRCULATION BETWEEN 94W 
AND 113W...AND THIS AREA WILL REMAIN QUITE ACTIVE CONVECTIVELY 
FOR THE NEXT DAY OR SO. IN FACT...A LARGE SWATH OF 20-30 KT SELY 
WINDS IS CROSSING THE EQUATOR AND FLOWING INTO THE S SIDE OF 
THIS EPAC MONSOON TROUGH/ITCZ... YIELDING A SUBSTANTIAL AREA OF 
20-25 KT S TO SW WINDS ON THE S SIDE OF THIS TROUGH...AND AIDING 
IN STRONG LOW LEVEL CONVERGENCE AND DEEP CONVECTION. GLOBAL 
MODELS HAVE BEEN KEYING IN ON THE POSSIBLE DEVELOPMENT OF A LOW 
PRESSURE SYSTEM IN THIS REGION AS THIS CROSS HEMISPHERIC FLOW 
LIFTS THE E END OF MONSOON TROUGH/ITCZ NWD TO NEAR THE MEXICAN 
COASTLINE BETWEEN 48-72 HOURS.

OTHERWISE...A FLAT PRESSURE GRADIENT IS OBSERVED AT THE SURFACE 
WITH A WEAK RIDGE BETWEEN THE LOW THAT IS THE REMNANT OF LINDA 
NEAR 21N133W AND THE COLD FRONT OVER THE FAR NORTHWEST PART.

$$
STRIPLING