000
AXPZ20 KNHC 110258
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC TUE SEP 11 2012

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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0045 UTC.

...SPECIAL FEATURE...

A BROAD AREA OF LOW PRESSURE EMBEDDED IN THE MONSOON TROUGH NEAR 
12.5N99W IS MOVING W-NW AROUND 10 KT. EASTERLY WINDS TO 25 KT 
ARE WITHIN 210 NM OF THE CENTER OVER THE N AND NE QUADRANTS AS 
SEEN BY SHIP MCZN2 AT 1800 UTC AS WELL AS THE 1854 UTC OSCAT 
PASS. THIS LOW LIES IN AN AREA OF SW SWELL AND HAS SEAS TO 10 
FT. ISOLATED MODERATE TO STRONG CONVECTION WAS WITHIN 270 NM N 
SEMICIRCLE OF THE LOW PRES SYSTEM...INCLUDING ALONG THE COAST OF 
SOUTHERN MEXICO. ENVIRONMENTAL CONDITIONS REMAIN CONDUCIVE FOR 
THE FORMATION OF A TROPICAL DEPRESSION OVER THE NEXT COUPLE OF 
DAYS. THIS LOW PRES SYSTEM IS CURRENTLY FORECAST TO GRADUALLY 
DEEPEN AND WINDS INCREASE TO 30 KT AS IT CONTINUES NORTHWESTWARD 
THROUGH WED EVENING.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...

THE MONSOON TROUGH AXIS WAS ANALYZED FROM 09N83W TO 10N91W TO 
LOW PRES NEAR 12.5N99W TO 14N109W TO 11N114W TO 09N134W. THE 
ITCZ AXIS WAS ANALYZED FROM 09N134W TO 09N140W. ISOLATED 
MODERATE TO STRONG CONVECTION WAS WITHIN 270 NM N SEMICIRCLE OF 
THE LOW PRES CENTER. SCATTERED MODERATE CONVECTION WAS S OF THE 
AXIS TO 07N BETWEEN 82W AND 85W...INCLUDING OVER PORTIONS OF 
COSTA RICA AND WESTERN PANAMA AS WELL AS WITHIN 60 NM OF THE 
MEXICAN COAST BETWEEN 86W AND 89W. SCATTERED MODERATE CONVECTION 
WAS ALSO WITHIN 180 NM S OF THE AXIS BETWEEN 100W AND 110W AND 
WITHIN 90 NM N OF AXIS W OF 128W. SCATTERED MODERATE TO STRONG 
CONVECTION WAS WITHIN 150 NM S OF THE AXIS BETWEEN 118W AND 
136W. 

...DISCUSSION...

A DEEP LAYERED LOW LIES OVER BAJA CALIFORNIA NORTE. SOUTHERLY 
FLOW ON THE EASTERN SIDE OF THIS LOW IS PUMPING MOISTURE 
NORTHWARD ALONG THE W COAST OF MEXICO INTO THE GULF OF 
CALIFORNIA. SCATTERED MODERATE CONVECTION WAS IN THE GULF OF 
CALIFORNIA N OF 29N AND WITHIN 60 NM OF THE E COAST OF BAJA 
CALIFORNIA FROM 24N TO 29N. THIS LOW IS FORECAST TO BE SLOWLY 
BUMPED NORTHEASTWARD BY A SHORTWAVE TROUGH CURRENTLY OFF THE 
CENTRAL CALIFORNIA COAST AS IT MOVES INLAND.

AN UPPER LEVEL ANTICYCLONE NEAR 19N104W EXTENDS RIDGE AXES 
SOUTHWESTWARD TO 15N140W AND SOUTHEASTWARD ALONG THE COAST AND 
NEAR THE LOW PRES SYSTEM DISCUSSED IN THE SPECIAL FEATURES 
SECTION TO 10N90W. A 30-50 KT E-NE JET LIES SE OF THE 
ANTICYCLONE IN THE REGION S OF 06N W OF 110W. THIS SHEAR IS 
INHIBITING THE DEVELOPMENT OF DEEP CONVECTION...BUT THE BROAD 
AREA OF DIFFLUENCE ALOFT BETWEEN THIS JET AND THE RIDGE AXIS IS 
ENHANCING THE SCATTERED MODERATE CONVECTION ALONG THE MONSOON 
TROUGH AND ITCZ DESCRIBED IN THE SECTION ABOVE. 

THE 1029 MB SUBTROPICAL HIGH WAS ANALYZED NEAR 38N152W. THE HIGH 
IS FORECAST TO SHIFT NORTHEASTWARD OVER THE NEXT FEW DAYS. THE 
1804 UTC AND 1944 ASCAT PASSES SHOWED THE STRONG TRADE WINDS 
THAT WERE OVER W WATERS EARLIER TODAY HAVE MOVED W OF THE 
FORECAST AREA. THE RESIDUAL SWELL FROM THE TRADE WINDS IS 
EXPECTED TO SUBSIDE BELOW ADVISORY CRITERIA LATE TONIGHT. 

HIGH PRES BUILDING SOUTHWARD OVER THE GULF OF MEXICO BEHIND A 
COLD FRONT AND THE NORTHWARD MIGRATION OF THE MONSOON TROUGH 
NEAR THE LOW PRES SYSTEM DISCUSSED IN THE SPECIAL FEATURES 
SECTION WILL INCREASE THE PRES GRADIENT OVER CENTRAL AMERICA. 
FRESH NE TO E WINDS ARE EXPECTED DOWNWIND OF THE GULF OF 
PAPAGAYO BEGINNING TUE MORNING AS A RESULT. WINDS MAY BRIEFLY 
PULSE TO A STRONG BREEZE IN THE EARLY MORNING HOURS WED WITH THE 
ASSISTANCE OF DRAINAGE FLOW OFF THE LAND.

ON WED...A NEW BATCH OF SW SWELL WILL CROSS THE EQUATOR. SEAS TO 
9 FT ARE EXPECTED S OF 03N BETWEEN 110W AND 130W BY WED EVENING.

$$
SCHAUER