000
AXPZ20 KNHC 150958
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC WED SEP 15 2010

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 
0915 UTC.

...ITCZ...
AXIS ALONG 14N95W TO 10N107W TO 12N119W TO 10N130W TO 11N140W.  
SCATTERED MODERATE ISOLATED STRONG CONVECTION WITHIN 120 NM S 
AND 90 NM N OF AXIS FROM 106W TO 119W.

...DISCUSSION...
SHARP UPPER LEVEL TROUGH CROSSES BASIN FROM 32N125W TO 17N140W 
BRING STRONG SUBSIDENCE WITHIN 5 DEGREES OF ITS AXIS PRODUCING 
VERY DRY AIR MASS.  COMPLEX DOUBLE ANTICYCLONES...ONE OVER 
CENTRAL MEXICO AND ANOTHER OVER BAJA CALIFORNIA PENINSULA... 
WITH SHEAR ZONE BETWEEN THEM HELP ADVECT PLENTY OF TROPICAL 
MOISTURE ACROSS CENTRAL AMERICA INTO E PAC ALONG ITCZ LATITUDES. 
ANOTHER ANTICYCLONE FURTHER E ENHANCES UPPER OUTFLOW TO TROPICAL 
STORM KARL NOW APPROACHING YUCATAN PENINSULA.  ELSEWHERE... E TO 
NE WIND FLOW ALOFT MAINTAINS PLENTY OF MOISTURE AVAILABLE FOR 
CONVECTION...BUT STRONG ENOUGH TO SHEAR ITS CYCLONIC DEVELOPMENT.

AT THE SURFACE...
HIGH PRES CENTER 1023 MB AT 28N143W HAS RIDGE EXTEND SE TO 
17N116W CONTRIBUTING TO MAINTAIN E PAC DRY N OF ITCZ W OF 120W. 
PRES GRADIENT WITH TROUGH ALONG CENTRAL CALIFORNIA TIGHT ENOUGH 
TO ALLOW FOR FRESH NW WINDS TO START WITHIN 24 HRS THROUGH FRI. 
WINDS ACROSS GULF OF TEHUANTEPEC DIMINISHING AS GRADIENT 
FLATTENS WITH APPROACH OF TROPICAL STORM KARL.  THEY MAY START 
AGAIN BEYOND FORECAST PERIOD DEPENDING OF KARL TRACK.  

AS ACTIVE LOW PRES CENTERS EITHER MOVE OUT OF DISSIPATE IN E PAC 
...MODEL GUIDANCE ITCHY TO DEVELOP NEW ONE NEAR 12N107W BY 48 
HRS WITH STRONG SW BREEZE EXTENDING 240 NM IN ITS SOUTHERN 
SEMICIRCLE.

CROSS EQUATORIAL LONG PERIOD SWELLS CONTINUE TO SPREAD THROUGH 
FORECAST PERIOD REACHING TO AS FAR NORTH AS 16N.  LARGE SURF 
ALONG EXPOSED COASTS IS EXPECTED WITHIN NEXT FEW DAYS AS SEAS UP 
TO 12 FT.

$$
WALLY BARNES