000
AXPZ20 KNHC 220934
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC TUE SEP 22 2009

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN
FROM THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0745 UTC.

...SPECIAL FEATURE...

AN AREA OF LOW PRESSURE 1009 MB IS NEAR 15N113W...ABOUT 520 NM 
S-SW OF THE SOUTHERN TIP OF BAJA CALIFORNIA. AN ASCAT PASS FROM 
0418 UTC SHOWED ONLY A SMALL AREA OF WINDS TO 20 KT JUST N OF 
THE LOW...BUT GIVEN THE INCREASE IN CONVECTION ASSOCIATED WITH 
THE SYSTEM AND THE STRENGTHENING PRES GRADIENT BETWEEN THE LOW 
AND THE HIGH PRES RIDGE TO ITS NW...BELIEVE WINDS IN THE NW 
QUADRANT ARE TO 20 KT. SCATTERED MODERATE CONVECTION CAN BE 
FOUND WITHIN 180 NM IN THE NW SEMICIRCLE OF THE LOW. THIS 
CONVECTION HAS BECOME MORE ORGANIZED SINCE THIS TIME YESTERDAY. 
THE NUMERICAL MODELS AGREE ON FURTHER DEVELOPMENT OF THIS SYSTEM 
AS IT TRACKS NW WITH A REGION OF UPPER LEVEL DIFFLUENCE BETWEEN 
AN ANTICYCLONE OVER MEXICO NEAR 20N100W AND AN UPPER LOW NEAR 
00N105W. THERE IS A HIGH CHANCE...GREATER THAN 50 PERCENT...OF 
THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

...THE ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE IS ALONG 07N78W TO 07N92W TO 
15N110W TO 09N133W TO 11N140W. SCATTERED MODERATE TO STRONG 
CONVECTION CAN BE FOUND WITHIN 180 NM N AND 90 NM S OF THE ITCZ 
AXIS E OF 83W. SCATTERED MODERATE CONVECTION LIES WITHIN 90 NM S 
OF AXIS BETWEEN 115W AND 118W.

...DISCUSSION...

N OF 20N...
TWO WEAK AREA OF LOW PRES REMAIN OVER THE DISCUSSION AREA. THE 
REMNANTS OF MARTY ARE DEPICTED AS A TROUGH FROM 26N128W TO 1015 
MB LOW PRES AT 23N129W TO 21N130W. THE 0240 UTC QUIKSCAT PASS 
CONTINUED TO SHOW NE WINDS IN THE N QUADRANT OF THE LOW IN THE 
20-25 KT RANGE. THIS PASS ALSO SHOWED THE LOW LEVEL CIRCULATION 
BECOMING MORE ELONGATED. WINDS AND SEAS ARE EXPECTED TO DIMINISH 
WITH THIS SYSTEM LATER TODAY. THE OTHER LOW IS A SMALL 
CIRCULATION NEAR 22N115W...ABOUT 290 NM W OF THE SOUTHERN TIP OF 
BAJA CALIFORNIA MOVING NW 5 KT. THE 0420 ASCAT PASS SHOWED WINDS 
LESS THAN 10 KT IN THE EASTERN SEMICIRCLE OF THE LOW AND THIS 
LOW IS EXPECTED TO WEAKEN TO A TROUGH LATER THIS MORNING. 
NEITHER LOW HAS ANY ASSOCIATED DEEP CONVECTION. WEAK HIGH PRES  
AND MOSTLY BROKEN STRATOCUMULUS WILL PERSIST ELSEWHERE OVER N 
WATERS THROUGH THE PERIOD WITH SOME CIRRUS EXPECTED ALONG THE 
40-50 KT WESTERLY JET DIRECTED FROM 20N140W 25N110W INTO THE 
SOUTHERN EDGE OF THE POSITIVELY TILTED UPPER TROUGH OVER THE 
SOUTHWEST U.S. AND NW MEXICO. THE UPPER TROUGH AND JET AXIS ARE 
EXPECTED TO REMAIN STATIONARY THE NEXT FEW DAYS. THE COLD FRONT 
ASSOCIATED WITH THIS TROUGH WILL PASS SOUTH INTO NORTHERN MEXICO 
LATER TODAY. MODELS SHOW INCREASING AGREEMENT ON WINDS 
INCREASING TO 20 KT OVER THE NORTHERN GULF OF CALIFORNIA...BUT 
THE WIND REPORTS BEHIND THE FRONT OVER THE PAST FEW HOURS HAVE 
BEEN LESS THAN IMPRESSIVE. HELD OFF ON ANY MENTION OF WINDS 
ABOVE 20 KT IN THE HIGH SEAS FORECAST AS A RESULT.

S OF 20N...
AN UPPER LEVEL RIDGE AXIS SPAWNING FROM A SMALL ANTICYCLONE 
CENTERED NEAR THE GULF OF FONSECA AND EXTENDING SE INTO THE GULF 
OF PANAMA IS GENERATING DIFFLUENCE ALOFT. THE RESULTING VERTICAL 
LIFT OF THE LOW LEVEL MOISTURE POOLED ALONG THE ITCZ OVER THE 
FAR EASTERN WATERS IS THE IMPETUS FOR THE SCATTERED MODERATE TO 
STRONG CONVECTION FOUND WITHIN 180 NM N AND 90 NM S OF THE ITCZ 
AXIS E OF 83W. THE SMALL ANTICYCLONE IS EXPECTED TO MERGE WITH 
THE LARGER ANTICYCLONE OVER MEXICO LATER TODAY. WHILE CONDITIONS 
SHOULD STILL REMAIN BROADLY DIFFLUENT OVER THIS AREA 
ALOFT...CONFIDENCE IS LOW IN THE GFS FORECAST WHICH GENERATES A 
REGION OF STRONG UPPER LEVEL DIFFLUENCE E OF 84W THAT INDUCES A 
1005 MB LOW PRES SYSTEM OFF THE SOUTHERN TIP OF PANAMA WITH 
SOUTHWESTERLY WINDS OF 20-30 KT AND SEAS TO 9 FT BY 1800 UTC 
TODAY. THIS IS CONSIDERABLY STRONGER THAN ANY OTHER MODEL. THE 
ASCAT PASS FROM 0234 UTC SHOWED ONLY A SMALL AREA OF S TO SW 
WINDS IN THE 15-20 KT RANGE CURRENTLY FEEDING INTO THIS AREA OF 
CONVECTION AND SEAS ARE TO 8 FT IN SW SWELL. THEREFORE...THE 
FORECAST FOLLOWS THE MODEL CONSENSUS AND CALLS FOR WINDS AND 
SEAS TO DIMINISH HERE OVER THE NEXT 24 HOURS AS THE DIFFLUENCE 
ALOFT DECREASES. ELSEWHERE ASIDE FROM THE PREVIOUSLY MENTIONED 
SYSTEMS...A WEAK SURFACE TROUGH FOUND ALONG 130W FROM 06N TO 14N 
IS CAUSING A WEAK PERTURBATION IN THE ITCZ. CONVECTION HAS 
INCREASED OVER THE LAST 24 HOUR NEAR THE TROUGH...WITH ISOLATED 
MODERATE CONVECTION CURRENTLY WITHIN 180 NM W AND 75 NM W OF THE 
TROUGH ALONG FROM 06N TO 13N. 

GAP WINDS...
THE COLD FRONT PASSING SOUTH INTO MEXICO TODAY IS EXPECTED TO 
BRING NORTHERLY FLOW THROUGH THE BAY OF CAMPECHE INTO THE GULF 
OF TEHUANTEPEC IN APPROXIMATELY 48 HOURS. WINDS ARE EXPECTED TO 
INCREASE ABOVE 20 KT BY EARLY THU MORNING.

$$
SCHAUER CLARK