000
AXPZ20 KNHC 090915
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC WED SEP 09 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 
0900 UTC.

...SPECIAL FEATURES...

AT 09/0900 UTC...TROPICAL STORM LINDA IS LOCATED NEAR 15.8N 
128.4W MOVING SLOWLY N-NW OR 340 DEG AT 2 KT. MAXIMUM SUSTAINED 
WINDS ARE 55 KT WITH GUSTS TO 65 KT. ESTIMATED MINIMUM CENTRAL 
PRESSURE IS 994 MB. SEE LATEST NHC FORECAST/ADVISORY UNDER 
AWIPS/WMO HEADERS MIATCMEP5/WTPZ25 KNHC FOR MORE DETAILS. THE 
CLOUD PATTERN ASSOCIATED WITH LINDA HAS CHANGED LITTLE OVERNIGHT 
WITH MODERATE TO STRONG CONVECTION WITHIN 70 NM OF CENTER. LINDA 
IS FORECAST TO SLIGHTLY STRENGTHEN DURING THE NEXT 12-24 
HOURS...BUT BEYOND THIS PERIOD THE SHEAR IS FORECAST TO INCREASE 
AND THE CYCLONE IS EXPECTED TO BE MOVING OVER SLIGHTLY COOLER 
WATER. THESE FACTORS SHOULD INDUCE WEAKENING. IN ABOUT 72 
HOURS...LINDA IS EXPECTED TO BE A TROPICAL DEPRESSION.

...THE ITCZ...

THE ITCZ AXIS IS ALONG 09N84W TO 08N90W TO 11N105W TO 10N115W TO 
12N124W...THEN CONTINUING FROM 11N132W TO 09N140W. A CLUSTER OF 
MODERATE TO STRONG CONVECTION IS N OF 06N AND E OF 80W INCLUDING 
THE GULF OF PANAMA. SCATTERED MODERATE CONVECTION IS NOTED 
WITHIN 180 NM S OF AXIS BETWEEN 90W AND 110W. SCATTRED MODERATE 
TO ISOLATED STRONG CONVECTION IS FROM 06N TO 11N BETWEEN 120W 
AND 125W. 

...DISCUSSION...

A DEEP LAYER UPPER ANTICYCLONE LOCATED W OF 140W HAS A RIDGE 
AXIS EXTENDING EWD OVER THE FAR WESTERN PORTION OF THE FORECAST 
REGION...AND TO WITHIN 4-5 DEGREES TO THE W OF LINDA. THE RIDGE 
AND THE ASSOCIATED DRY STABLE AIR AT THE MIDDLE AND UPPER LEVELS 
OF THE ATMOSPHERE COVERS ROUGHLY THE AREA FROM 10N TO 20N W OF 
130W. A SHARP MID/UPPER LEVEL TROUGH IS MOVING ACROSS THE NW 
PORTION OF THE AREA AND EXTENDS FROM 31N128W TO 22N140W.  
ANOTHER UPPER LEVEL ANTICYCLONIC CIRCULATION CENTERED OVER 
SOUTH-CENTRAL MEXICO HAS A RIDGE EXTENDING WWD TO NEAR 124W.  
THIS PATTERN HAS ACTED TO BLOCK TROPICAL STORM LINDA IN BETWEEN 
TWO RIDGES...TO THE E AND W...AND A BROAD UPPER TROUGH TO THE 
N...ALL LEAVING LINDA TRAPPED IN BETWEEN THESE SYSTEMS. 
ACCORDING TO THE COMPUTER MODELS...THE TROUGH IS FORECAST TO  
WEAKEN THE RIDGE WEST OF LINDA ALLOWING THE CYCLONE TO MOVE 
FASTER TOWARD THE NORTH-NORTHWEST. THE BASE OF STRONG UPPER 
LEVEL TROUGH LYING OVER THE CARIBBEAN SEA REACHES COSTA RICA AND 
PANAMA. UPPER LEVEL DIFFLUENCE AHEAD OF THIS SYSTEM IS HELPING 
TO INDUCE THE MODERATE TO STRONG CONVECTION OVER THE GULF OF 
PANAMA. CONVECTION HAS ALSO FLARED UP ALONG THE COAST OF EL 
SALVADOR AND GUATEMALA AND ADJACENT COASTAL WATERS.  

A SURFACE RIDGE CONTINUES TO DOMINATE THE NORTHERN PORTION OF 
DISCUSSION AREA MAINLY N OF 20N W OF 115W. THE PRESSURE GRADIENT 
BETWEEN LINDA AND THE RIDGE IS PRODUCING A LARGE AREA OF NE 
WINDS 20 KT AND SEAS TO 9 FT PARTICULARLY FROM 15N TO 25N AND W 
OF 135W. THESE CONDITIONS ARE EXPECTED TO PERSIST DURING THE 
NEXT 48 HOURS. 

SWELLS FROM THE NW ARE MOVING SE AND INTO THE NE PORTION OF THE 
AREA TONIGHT...OFFSHORE OF BAJA CALIFORNIA. FOR THE UPCOMING 
WEEKEND...LARGE LONG PERIOD W-NW SWELLS IN EXCESS OF 16 SECONDS  
WILL MOVE INTO THE NW PART OF THE AREA...BUILDING SEAS TO 11 FT 
BY SATURDAY MORNING. CROSS EQUATORIAL SLY WINDS OF 20 KT AND 
SWELLS GENERATED BY A BROAD FIELD OF SE WINDS OFF THE COAST OF 
ECUADOR AND PERU WILL AFFECT THE FAR SOUTHERN PORTION MAINLY S 
OF 05N BETWEEN 92W AND 100W BY 24 HOURS. 

$$
GR