000
AXPZ20 KNHC 172202
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC THU SEP 17 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 
2130 UTC.

...SPECIAL FEATURES...

TROPICAL STORM MARTY WAS LOCATED NEAR 19.7N 113.2W AT 17/2100 
UTC...MOVING VERY LITTLE. MAXIMUM SUSTAINED WIND SPEED WAS 40 
KT WITH GUSTS TO 50 KT. ESTIMATED MINIMUM CENTRAL PRESSURE WAS 
1002 MB. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO 
HEADERS MIATCMEP1/WTPZ21KNHC FOR MORE DETAILS. THE CONVECTIVE 
PATTERN WITH MARTY HAD BECOME ELONGATED AND SOMEWHAT ELLIPTICAL 
THIS AFTERNOON...WITH THE DEEPEST CONVECTION MAINLY N OF THE LOW 
LEVEL CENTER. MODEST SLY WIND SHEAR CONTINUES TO INFLUENCE THIS 
NORTHERLY DISPLACEMENT OF THE CONVECTION OF MARTY...AND UPPER 
SHEAR IS FORECAST TO INCREASE FROM THE SW WITHIN THE NEXT 24 
HOURS. THIS WIND SHEAR AND A DRIER MORE STABLE AIRMASS LOCATED 
UPSTREAM IN THE ENVIRONMENT THAT MARTY IS EXPECTED TO MOVE INTO 
SHOULD INDUCE A WEAKENING TREND FOR THE STORM TONIGHT. MARTY IS 
EXPECTED TO BEGIN MOVING SLOWLY NORTH-NORTHWESTWARD TONIGHT AS A 
WEAK RIDGE STRENGTHENS EAST OF THE CYCLONE...AND THEN ACCELERATE 
AND MOVE MORE NW AND THEN W OVER THE NEXT SEVERAL DAYS. 

AN AREA OF DISTURBED WEATHER OCCURRING OFF OF THE SOUTHWEST 
COAST OF MEXICO SOME 100 MILES SOUTH OF ZIHUATANEJO MEXICO...IS 
BEING MONITORED FOR POSSIBLE TROPICAL DEVELOPMENT. DEEP 
CONVECTION HAS BEEN LINGERING ACROSS THIS GENERAL AREA FOR OVER 
24 HOURS...UNDER THE POSITIVE INFLUENCE OF DIFFLUENT FLOW ALOFT 
OCCURRING ON THE S SIDE OF UPPER RIDGING ACROSS THIS AREA. A 
LARGE CLUSTER OF DEEP CONVECTION BLOSSOMED LAST NIGHT...AND AS 
IT WEAKENED THIS MORNING SOME MID LEVEL CYCLONIC TURING COULD BE 
SEEN IN SATELLITE IMAGERY...THROUGH THIS AFTERNOON. CONVECTION 
HAS SINCE DIMINISHED FURTHER...AND AFTERNOON VISIBLE SATELLITE 
IMAGERY AT 1900 UTC REVEALED A SMALL TIGHT LOW LEVEL CLOUD SWIRL 
EMERGING FROM THE WEAKENING CONVECTION...NEAR 16.4N 102.8W... 
MOVING W FOR THE MOMENT. 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 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 WAS ANALYZED ALONG 129W MOVING W 15 KT. THERE IS 
ONLY ISOLATED CONVECTION WAS NOTED NEAR THIS WEAK 
PERTURBATION. 

A TROPICAL WAVE WAS ANALYZED ACROSS THE FAR W CARIBBEAN ALONG 
84W AND EXTENDED S INTO THE EPAC INTO THE ITCZ THERE. CONVECTION 
WITHIN THE ITCZ WAS NOTED NEAR THIS WAVE AXIS.

...THE ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE WAS ANALYZED FROM 10N85W TO 
11N102W THEN CONTINUING ALONG 14N116W TO 12N131W TO 09N140W. 
SCATTERED MODERATE TO ISOLATED STRONG WITHIN 160 NM S OF AXIS E 
OF 92W...AND FROM 06N TO 11N BETWEEN 100W AND 106W.

...DISCUSSION...

N OF 20N...A SURFACE RIDGE...ANCHORED ON A 1027 MB HIGH PRES 
NEAR 34N140W...HAS BECOME STATIONARY OVER THE FAR N AND NW 
WATERS COVERING ROUGHLY THE AREA N OF 20N W OF 120W. THIS REGION 
IS MARKED BY MODERATE TO STRONG SUBSIDENCE AND BROKEN TO 
OVERCAST STRATOCUMULUS CLOUDS WIDESPREAD ACROSS THE AREA S TO 
NEAR THE ITCZ AND SE TO NEAR MARTY. THIS RIDGE WAS PRODUCING 
TRADE WINDS OF 20 KT AND SEAS 8 TO 9 FT BETWEEN 14N AND 21N W OF 
128W. THE LEADING EDGE OF A COLD FRONT HAS STALLED ACROSS THE 
FAR NW CORNER OF THE AREA AND WAS DISSIPATING E OF 125W. A 
DEEP-LAYER TROUGH ACROSS THE FAR NE PACIFIC HAS LIFTED NE INTO 
THE PACIFIC NW...WITH ANOTHER LARGE UPPER LOW EXPECTED TO 
REINFORCE THIS FRONT OVER THE WEEKEND. WAVE HEIGHTS HAVE BUILT 
INTO THE 8 TO 10 FT RANGE IN W-NW SWELL TODAY OVER THESE NW 
WATERS...AND WILL PERSIST THROUGH FRI AS ANOTHER PULSE OF NLY 
WIND SWELL MOVES FROM OFFSHORE CALIFORNIA INTO THE AREA.

A DIFFLUENT PATTERN ALOFT ASSOCIATED WITH THE UPPER LEVEL RIDGE 
EXTENDING FROM THE SRN GULF OF MEXICO W TO MARTY WAS HELPING TO 
VENTILATE AND SUSTAIN A SEVERAL AREAS OF DEEP CONVECTION OVER 
THE EPAC WATERS S OF 20N AND E OF 110W ACROSS THE ITCZ.  

WAVE HEIGHTS ARE GENERALLY RUNNING AT 8 TO 9 FT OVER MUCH OF THE 
FORECAST AREA PRIMARILY IN NW SWELL. NEW PULSES OF S-SW LONG 
PERIOD SWELL WILL MOVE INTO THE WATERS DURING THE NEXT FEW DAYS 
AND MIX WITH LONG PERIOD W AND NW SWELL...AND RAISE WAVE HEIGHTS 
ABOVE 8 FT E OF 110W...TONIGHT THROUGH THE WEEKEND.

$$
STRIPLING