000
AXPZ20 KNHC 160928
TWDEP 

TROPICAL WEATHER DISCUSSION      
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC WED MAY 16 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 
0845 UTC.

...SPECIAL FEATURE...
TROPICAL STORM ALETTA IS CENTERED NEAR 11.9N 111.7W AT 16/0900 
UTC MOVING W-NW OR 285 DEG AT 8 KT. THIS MOTION IS EXPECTED TO 
CONTINUE DURING THE NEXT DAY OR SO. ESTIMATED MINIMUM CENTRAL 
PRES 1004 MB. MAXIMUM SUSTAINED WINDS 35 KT GUSTS TO 45 KT.  
PLEASE REFER TO THE LATEST PUBLIC ADVISORY TCPEP1/WTPZ31 KNHC 
FOR MORE DETAILS. SCATTERED MODERATE TO STRONG CONVECTION IS 
NOTED WITHIN 90 NM W SEMICIRCLE AND 90 NM NE QUADRANT OF CENTER. 
A GRADUAL WEAKENING IS FORECAST DURING THE NEXT 48 HOURS AS 
VERTICAL SHEAR INCREASES AND DRY AIR APPROACHES. 

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
MONSOON TROUGH FROM 09N83W TO LOW PRES NEAR 08N97W 1010 MB TO 
13N108W...THEN RESUMES FROM 09N111W TO 06N120W. ITCZ FROM 
06N120W TO 03N140W. CLUSTER OF MODERATE TO STRONG CONVECTION 
FROM 10N TO 12N BETWEEN 97W AND 100W. SCATTERED MODERATE TO 
ISOLATED STRONG CONVECTION IS FROM 05N TO 11N BETWEEN 100W AND 
110W. 

...DISCUSSION...
ALOFT...MID/UPPER LEVEL RIDGE WITH AXIS ROUGHLY ALONG 128W 
CONTINUES TO DOMINATE THE N WATERS WHILE A DEEP LAYER TROUGH 
PERSISTS BETWEEN 140W AND THE HAWAIIAN ISLANDS. S AND SW WINDS 
AHEAD OF THIS TROUGH ARE TRANSPORTING ABUNDANT MID/UPPER LEVEL 
MOISTURE ACROSS THE NW CORNER OF THE FORECAST AREA. STRONG 
SUBSIDENCE AND IMPLIED DRY AIR MASS COVERS THE AREA N OF 20N E 
OF 120W INCLUDING THE BAJA CALIFORNIA PENINSULA AND NW MEXICO.  
AN ANTICYCLONIC CIRCULATION REMAINS CENTERED OVER NORTHERN 
CENTRAL AMERICA WITH A RIDGE DOMINATING THE WATERS E OF 110W. 
THIS FEATURE IS PROVIDING A FAVORABLE ENVIRONMENT FOR ACTIVE 
TSTMS E OF 110W.

AT LOWER LEVELS...A SURFACE RIDGE EXTENDS SE FROM 1026 MB HIGH 
PRES NEAR 35N135W TO AROUND 20N115W. A SURFACE TROUGH IS 
ANALYZED ALONG THE WEST COAST OF MEXICO. THE RESULTING PRES 
GRADIENT BETWEEN THE RIDGE AND THE TROUGH IS PRODUCING AN AREA 
OF FRESH NW WINDS NEAR THE COAST OF BAJA CALIFORNIA N OF 25N E 
OF 118W. SCATTEROMETER DATA ALONG WITH FEW SHIP OBSERVATIONS 
SHOWED WINDS OF 20 TO 25 KT IN THIS AREA. A WINDSAT PASS ALSO 
INDICATED FRESH TRADE WINDS COVERING THE REGION FROM 09N TO 21N 
W OF 130W. THE HIGH IS EXPECTED TO REMAIN NEARLY STATIONARY AND 
WEAKEN DURING THE NEXT 24 HOURS. AS A RESULT...EXPECT WINDS TO 
DIMINISH BELOW 20 KT.  

THE EDGE OF AN 0408 UTC ASCAT PASS CAPTURED THE CYCLONIC 
CIRCULATION ASSOCIATED WITH THE WEAK LOW PRES LOCATED NEAR 
08N97W ALONG THE MONSOON TROUGH. LOW LEVEL CYCLONIC TURNING IS 
ALSO NOTED IN SATELLITE IMAGERY. THIS SYSTEM WILL DRIFT W-NW 
OVER THE NEXT COUPLE OF DAYS. A WEAK TROUGH IS ALONG 126W FROM 
04N TO 08N. ONLY A FEW SHOWERS ARE ASSOCIATED WITH THIS FEATURE 
FORECAST TO DRIFT WWD DURING THE NEXT COUPLE OF DAYS. 

HIGH PRES BUILDING SOUTHWARD ALONG THE GULF COAST OF MEXICO WILL
INDUCE FRESH TO STRONG N-NE FLOW INTO THE GULF OF TEHUANTEPEC 
TODAY THROUGH EARLY FRI. 

$$
GR