000
AXPZ20 KNHC 121521
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SAT SEP 12 2010

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

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1500 UTC.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE AXIS IS ANALYZED FROM 09N83W 
TO 07N90W TO 12N112W THEN RESUMES NEAR 12N115W TO 11N123W THEN 
RESUMES NEAR 11N127W TO 13N133W THEN RESUMES NEAR 13N136W TO 
12N140W. THERE ARE THREE 1011 MB LOW PRES SYSTEMS EMBEDDED IN 
THE ITCZ. THE LOW NEAR 12N113W HAS SCATTERED MODERATE CONVECTION 
WITHIN 120 NM OF ITS S SEMICIRCLE. THE LOW PRES SYSTEM NEAR 
11N125W HAS SCATTERED MODERATE WITHIN 120 NM OF IT S SW AND W 
QUADRANTS. FINALLY...THE WESTERN LOW PRES IS NEAR 13N134W AND 
HAS SCATTERED MODERATE WITHIN 120 NM OF CENTER. ELSEWHERE... 
SCATTERED MODERATE CONVECTION LIES WITHIN 120 NM OF THE ITCZ 
AXIS BETWEEN 86W AND 92W.


...DISCUSSION...

AN EXPANSIVE ANTICYCLONE CENTERED OVER SE TEXAS EXTENDS A RIDGE 
SOUTHWEST TO 14N110W. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH 
THIS RIDGE IS ENHANCING THE SCATTERED MODERATE CONVECTION FOUND 
WITHIN 120 NM OF THE COAST OF MEXICO BETWEEN 102W AND 106W S OF 
20N. BROAD UPPER LEVEL DIFFLUENCE CAN ALSO BE FOUND BETWEEN THE 
E TO SE FLOW ON THE FAR SW SIDE OF THE ANTICYCLONE AND CYCLONIC 
FLOW ALOFT BETWEEN TWO UPPER LOWS CENTERED NEAR 00N96W AND 
03N114W. THIS DIFFLUENCE IS ENHANCING CONVECTION ON THE EASTERN 
EDGE OF THE ITCZ BETWEEN 86W AND 92W. N WINDS FUNNELING THROUGH 
THE ISTHMUS OF TEHAUNTEPEC ARE EXPECTED TO BE IN THE 20-25 KT 
RANGE FOR THE NEXT FEW DAYS AS A SURFACE TROUGH LINGERS FROM THE 
SW GULF OF MEXICO INTO THE ISTHMUS...DIRECTING NORTHERLY FLOW ON 
ITS W SIDE FROM HIGHER PRES OVER THE NORTHERN GULF COASTAL PLAIN 
SOUTHWARD INTO THE EASTERN PACIFIC.

A NEGATIVELY TILTED UPPER TROUGH EXTENDING FROM N OF AREA 
THROUGH 32N124W TO 25N120W IS ATTEMPTING TO PICK UP A WEAK UPPER 
LOW LOCATED NEAR 19N125W. HOWEVER...THE FORECAST CALLS FOR THE 
LEADING EDGE OF THE TROUGH TO MOVE NE INTO CALIFORNIA 
TODAY...LEAVING THIS LOW BEHIND. A REINFORCING SHOT OF SHORTWAVE 
ENERGY WILL MEET UP WITH THIS TROUGH OFF THE CALIFORNIA COAST 
MON...MAINTAINING THE MEAN TROUGH THERE AND TURNING THE FLOW 
ALOFT MORE ZONAL TO THE W OF THE TROUGH AXIS. A 
WEST-SOUTHWESTERLY UPPER JET IS ALREADY MOVING INTO FAR NW 
WATERS BEHIND THIS TROUGH. THE REFLECTION OF THIS TROUGHING AT 
THE SURFACE IS EXPANDING THE USUAL TROUGHING OVER THE GULF OF 
CALIFORNIA NORTHWARD INTO CALIFORNIA AND OFFSHORE. THE INCREASED 
PRES GRADIENT BETWEEN THIS TROUGHING AND THE SUBTROPICAL 
RIDGE...WHICH LIES FROM A 1023 MB HIGH NEAR 36N139W THROUGH 
32N134W TO 17N115W...IS YIELDING NW TO N WINDS AROUND 15 KT OFF 
THE COAST OF CENTRAL BAJA CALIFORNIA ACCORDING TO THE 0514 UTC 
ASCAT PASS. 

0510 UTC ASCAT RETRIEVALS SHOW SOUTHWESTERLY WINDS TO 20 KT 
FEEDING INTO THE LOW PRES SYSTEM NEAR 12N113W. THESE WINDS ARE 
EXPECTED TO EXPAND ALONG THE SOUTHERN SIDE OF THE ITCZ OVER THE 
NEXT FEW DAYS AS THIS LOW DIMINISHES. SEAS IN THIS AREA ARE ALSO 
EXPECTED TO REMAIN AROUND 8 FT AS A NEW SURGE OF SW SWELL PUSHES 
INTO THIS AREA ON MON. THE 0650 UTC ASCAT PASS SHOWS 20 TO 25 KT 
NORTHERLY WINDS FEEDING INTO THE LOW PRES SYSTEM NEAR 13N134W. 
THESE CONDITIONS ARE EXPECTED TO CONTINUE AS THIS LOW REMAINS 
RELATIVELY STATIONARY AND BUTTED AGAINST THE SOUTHERN EDGE OF 
SUBTROPICAL HIGH PRESSURE.

$$
SCHAUER