000
AXPZ20 KNHC 112148
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
2205 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2100 UTC.

...SPECIAL FEATURE...
A BROAD AREA OF LOW PRESSURE CENTERED NEAR 15N104W MOVING W-NW 
AT 10-15 KT IS EMBEDDED ALONG THE MONSOON TROUGH. EASTERLY WINDS 
TO 25 KT ARE IN THE NE SEMICIRCLE OF THE LOW ALONG THE SOUTHERN 
COAST OF MEXICO BETWEEN 98W AND 103W. SCATTERED MODERATE 
ISOLATED STRONG CONVECTION EXISTS WITHIN 240 NM OF THE LOW. IT 
IS OF NOTE THAT THE GFS MODEL IS CURRENTLY INDICATING SE-E WINDS 
OF 30 TO 35 KT IN THE NORTHEAST QUADRANT OF THE LOW.  HOWEVER 
...A 1600 UTC ASCAT SCATTEROMETER PASS INDICATES THAT THE 
MAXIMUM WINDS WERE ONLY 20 TO 25 KT.  THUS THE GFS WINDS AND THE 
DERIVED WAVE HEIGHTS IN THE WAVEWATCH MODEL ARE TOO HIGH AT THE 
INITIAL...AND LIKELY DAY ONE...TIME PERIODS.  ENVIRONMENTAL 
CONDITIONS ARE CONDUCIVE FOR TROPICAL CYCLOGENESIS DURING THE 
NEXT TWO DAYS AS THE VERTICAL SHEAR SHOULD REMAIN MODERATE OUT 
OF THE NORTHEAST AND THE SYSTEM WILL STAY OVER WARM WATERS. THE 
DISTURBANCE IS EXPECTED TO INTENSIFY AS IT MOVES NORTHWEST JUST 
OFFSHORE OF THE MEXICAN COAST.  THE GFS AND UKMET GLOBAL MODELS 
ARE MORE AGGRESSIVE WITH ITS INTENSIFICATION...WHILE THE ECMWF 
AND NOGAPS SHOW ONLY A SMALL AMOUNT OF DEVELOPMENT.  SOMEWHAT 
COMPLICATING THE PREDICTION IS THAT A SEPARATE LOW IS SUGGESTED 
TO OCCUR ALONG THE MONSOON TROUGH SOUTHWEST OF THE CURRENT LOW.  
THIS COULD...IF IT OCCURS...AFFECT THE EVENTUAL TRACK AND 
INTENSITY OF THE EXISTING LOW. THE GRIDDED FORECAST WILL BE A 
BLEND OF THE GFS AND UKMET MODELS.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
MONSOON TROUGH EXTENDS FROM 09N83W TO 07N89W TO LOW PRES NEAR 
15N104W TO 12N118W TO 08N138W. ITCZ THEN BEGINS AND EXTENDS 
BEYOND 08N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION 
EXISTS WITHIN 180 NM OF AXIS BETWEEN 100W AND 108W. ISOLATED 
MODERATE CONVECTION EXISTS WITHIN 120 NM N OF TROUGH E OF 97W. 
SCATTERED MODERATE CONVECTION EXISTS WITHIN 60 NM OF AXIS 
BETWEEN 121W AND 132W.

...DISCUSSION...
A 1030 MB SUBTROPICAL HIGH PRESSURE IS CENTERED N OF THE AREA 
WITH RIDGING EXTENDING SOUTHEAST FROM THE HIGH ALONG THE 
NORTHERN PORTION OF THE DISCUSSION AREA.  THE PRESSURE GRADIENT 
FROM THE RIDGE EQUATORWARD TO THE MONSOON TROUGH IS MODEST AND 
THUS THE TRADEWINDS ARE WEAK AND BELOW OUR 25 KT CRITERION FOR 
THE HIGH SEAS.  SW WINDS ON THE EQUATORWARD SIDE OF THE MONSOON 
TROUGH ARE ALSO RELATIVELY WEAK FOR THIS TIME OF YEAR.  A WEAK 
GULF OF PAPAGAYO GAP WIND EVENT IS OCCURRING...BUT NE-E WINDS AS 
SEEN IN THE 1600 UTC ASCAT SCATTEROMETER PASS ARE AT 20 KT.  
THESE SHOULD NOT REACH THE 25 KT HIGH SEAS CRITERION BUT MAY 
CONTINUE AROUND 20 KT THROUGH FRIDAY.

$$
CHRIS LANDSEA