000
AXPZ20 KNHC 190928
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC MON SEP 19 2011

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS 
BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND 
METEOROLOGICAL ANALYSIS.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0845 UTC.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH AXIS EXTENDS W ACROSS COSTA RICA FROM 09N84W 
TO 12N92W TO LOW PRES NEAR 09N100W 1010 MB TO 09N103W. THE 
TROUGH IS THEN DISCONTINUOUS...RESUMING AT LOW PRES NEAR 16N112W 
1010 MB...TO LOW PRES NEAR 13N122W 1010 MB TO 09N140W. SCATTERED 
MODERATE ISOLATED STRONG CONVECTION NOTED WITHIN 120 NM EITHER 
SIDE OF AXIS BETWEEN 85W AND 95W. SCATTERED MODERATE CONVECTION 
WITHIN 120 NM OF AXIS BETWEEN 115W AND 125W.

...DISCUSSION... 

A 1024 MB SURFACE HIGH IS CENTERED NEAR 35N140W. GENERALLY LIGHT 
TO MODERATE TRADES ARE NOTED ON SCATTEROMETER DATA AND SHIP 
OBSERVATIONS S OF THE HIGH...EXCEPT JUST TO THE N OF THE MONSOON 
TROUGH WHERE WEAK LOW PRES IS KEEPING THE PRES GRADIENT TIGHT 
ENOUGH TO SUPPORT A SMALL AREA OF 20 KT WINDS. THE SURFACE HIGH 
PRES WILL CONTINUE TO WEAKEN THROUGH TODAY AS A DEEP LAYER 
TROUGH WELL NW OF THE AREA DIGS EASTWARD THROUGH THE N CENTRAL 
PACIFIC. THE AREAS OF FRESH TRADES W OF 125W N OF THE MONSOON 
TROUGH WILL SLOWLY DIMINISH AS A RESULT.

A 0206 UTC WINDSAT PASS SHOWED AN ELONGATED PERTURBATION ALONG 
THE MONSOON TROUGH NEAR 13N120W. THIS FEATURE ALSO SHOWED UP IN 
AN EARLIER 1804 UTC ASCAT PASS. WINDS TO 20 KT WERE NOTED BOTH 
TO THE NORTH AND SOUTH OF THE TROUGH AXIS BETWEEN 115W AND 125W. 
A WEAK LOW IS ANALYZED NEAR 13N122W AND GLOBAL MODEL CONSENSUS 
SHOWS IT PERSISTING IN THIS AREA THROUGH MID WEEK...ALTHOUGH 
WINDS DIMINISH AS THE HIGH PRES TO THE N WEAKENS. THE 
CONVERGENCE OF THE 20 KT WINDS INTO THE MONSOON TROUGH ALONG 
WITH UPPER DIVERGENCE ON THE SW SIDE OF AN UPPER RIDGE...ARE 
SUPPORTING CLUSTERS OF MODERATE CONVECTION IN THIS AREA.

FURTHER TO THE EAST ALONG THE MONSOON TROUGH...A 1010 MB SURFACE 
LOW IS CENTERED NEAR 16N113W. THIS FEATURE SHOWS UP WELL IN 
ASCAT DATA FROM 0514 UTC...BUT WINDS REMAIN FAIRLY LIGHT AND NO 
CONVECTION IS NOTED. 

WEAK RIDGING IS NOTED BETWEEN 105W AND 112W...EFFECTIVELY 
BREAKING THE MONSOON TROUGH. THE TROUGH CONTINUES AT 105W AND A 
0330 UTC ASCAT PASS SHOWED A WEAK CIRCULATION ALONG THE TROUGH 
NEAR 09N100W. THE GFS AND ECMWF SHOW INCREASING WINDS AND 
BUILDING SEAS AS THIS LOW DEEPENS AS IT MOVES NW OVER THE NEXT 
SEVERAL DAYS...TO INCLUDE FRESH GAP WIND FLOW THROUGH THE GULF 
OF TEHUANTEPEC. SCATTERED MODERATE CONVECTION IS NOTED ALONG THE 
MONSOON TROUGH AND OFF THE PACIFIC COAST OF CENTRAL AMERICA FROM 
COSTA RICA TO SOUTHERN MEXICO.
  
$$
CHRISTENSEN