000
AXPZ20 KNHC 021000
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SUN SEP 02 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0915 UTC.

...SPECIAL FEATURES...
TROPICAL STORM ILEANA...CENTERED AT 23.1N 120.4W AT 02/0300 UTC. 
ILEANA IS MOVING W OR 270 DEG AT 07 KT WITH AN ESTIMATED MINIMUM 
CENTRAL PRESSURE OF 1004 MB. MAXIMUM SUSTAINED WIND SPEED IS 35 
KT WITH GUSTS TO 45 KT. SCATTERED MODERATE CONVECTION IS NOTED 
WITHIN 90 NM NW AND WITHIN 30 NM SE SEMICIRCLES OF CENTER. THE 
CYCLONE IS MOVING OVER INCREASINGLY COOLER SEAS SURFACE WATERS 
AND MORE STABLE ATMOSPHERIC CONDITIONS AND IS EXPECTED TO WEAKEN 
TO A REMNANT LOW PRES TONIGHT. SEE THE LATEST NHC 
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP4/WTPZ24 KNHC 
FOR MORE DETAILS.

TROPICAL LOWS...LOW PRES IS AT 13.5N 104.5W WITH SCATTERED 
MODERATE ISOLATED STRONG CONVECTION NOTED WITHIN 120 NM OVER THE 
W SEMICIRCLE OF CENTER. A SECOND LOW PRES IS AT 16.5N104W 1007 
MB WITH SCATTERED MODERATE ISOLATED STRONG CONVECTION OBSERVED 
WITHIN 120 NM OF CENTER. GLOBAL GUIDANCE SUGGESTS THAT THESE 
SURFACE LOWS WILL MERGE REACHING NEAR 16N110W LATE SUN AND 
CONTINUE NW TO NEAR 17N114W ON MON WITH TROPICAL CYCLONE 
DEVELOPMENT LIKELY DURING THE 48 HOUR PERIOD. CURRENTLY THE 
PRESSURE GRADIENT BETWEEN STRONG HIGH PRESSURE BRIDGING SW 
ACROSS CENTRAL AMERICA AND LOW PRESSURE WITHIN THE BROAD MONSOON 
TROUGH HAS ENHANCED EASTERLY WINDS TO 20 TO 30 KT WITHIN 120 NM 
EITHER SIDE OF A LINE FROM 18N105W TO 13N97W. THE GRADIENT IS 
ALSO TIGHT OVER S SEMICIRCLE OF THE SOUTHERNMOST SURFACE LOW AND 
S TO SW WINDS ARE AT 20 TO 25 KT WITH SEAS 9 TO 10 FT WITHIN THE 
AREA FROM 10N TO 13N BETWEEN 101W AND 110W. 

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
MONSOON TROUGH AXIS FROM 09N84W TO 08N100W THEN RESUMES FROM 
1006 MB SURFACE LOW PRES AT 14N106W 09N132W TO BEYOND 11N140W. 
SCATTERED MODERATE ISOLATED STRONG CONVECTION WITHIN 75 NM OF 
08N100W.  SCATTERED MODERATE CONVECTION WITHIN 90 NM OF AXIS 
FROM 106W TO 113W.

...DISCUSSION...
BROAD UPPER LEVEL ANTICYCLONE AT 20N126W BRINGS DRY SUBSIDING 
AIR MASS INTO E PAC W OF 122W...DENTED ONLY BY W MOVEMENT OF 
T.S. ILEANA.  N OF ANTICYCLONE...DEEP LONGWAVE TROUGH ALOFT 
MOVES E WITH STRONG SHORT WAVE RUNNING FROM 32N126W TO 28N124W.  
DRY AIR AND STRONG SW WINDS CONTRIBUTE TO TEAR ILEANA APART...IN 
ADDITION TO COOL SEA SURFACE TEMPERATURES.  SECOND ANTICYCLONE 
NEAR BIG BEND TEXAS PROVIDES ABUNDANT TROPICAL MOISTURE INTO E 
PAC E OF 122W.  THIS RIDGE BRINGS MODERATE UPPER DIVERGENT FLOW 
INTO SCENARIO WITH SCATTERED DEEP CONVECTION DEVELOPING NEAR 
SURFACE LOW PRES 1006 MB NEAR 14N106W.  THIS LOW PRES...STILL 
EMBEDDED IN MONSOON FLOW...HAS A MODERATE PROBABILITY OF 
BUILDING INTO A TROPICAL CYCLONE WITHIN NEXT 48 HRS SINCE THE 
MAIN INGREDIENTS ARE IN PLACE.  
  
...ELSEWHERE AT THE LOW LEVELS...
SURFACE HIGH PRES CENTER 1029 MB N OF AREA AT 38N147W MAINTAINS 
MODERATE NE TRADES W OF ILEANA.

CROSS EQUATORIAL SWELL PROPAGATE N INTO BASIN S OF 20N E OF 135W 
ARE EXPECTED TO SUBSIDE BY MON.

$$
WALLY BARNES