000
AXPZ20 KNHC 220929
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SAT SEP 22 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 FEATURES...
TROPICAL DEPRESSION THIRTEEN-E CENTERED NEAR 13.7N 107.5W AT 
22/0900 UTC MOVING W OR 280 DEGREE AT 6 KT. ESTIMATED MINIMUM 
CENTRAL PRESSURE IS 1004 MB. MAXIMUM SUSTAINED WIND SPEED IS 30 
KT GUSTS TO 40 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER 
AWIPS/WMO HEADERS MIATCMEP3/WTPZ23 KNHC FOR MORE DETAILS. THIS 
TROPICAL CYCLONE IS EXPECTED TO BECOME A TROPICAL STORM LATER 
TODAY. THE OFFICIAL INTENSITY FORECAST INDICATES THAT THIS 
SYSTEM WILL CONTINUE TO GAIN STRENGTH AS IT IS EXPECTED TO 
REMAIN OVER 28-29C WATERS AND STAY IN AN FAIRLY LOW WIND SHEAR 
ENVIRONMENT DURING THE NEXT FEW DAYS. BASED ON THE CURRENT MODEL 
GUIDANCE...THIS SYSTEM IS NOT EXPECTED TO BE A THREAT TO LAND.
SCATTERED MODERATE TO STRONG CONVECTION IS NOTED WITHIN 120 NM E 
AND 60 NM W SEMICIRCLES OF CENTER. SCATTERED MODERATE ISOLATED 
STRONG CONVECTION CAN BE FOUND ELSEWHERE FROM 10N TO 17N BETWEEN 
100W AND 110W. 

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... 
MONSOON TROUGH EXTENDS FROM 08N84W TO 12N89W TO 10N95W TO 
13N100W THEN RESUMES W OF T.D. THIRTEEN-E FROM 12N117W TO 
09N130W. THE ITCZ CONTINUES FROM 90N130W TO BEYOND 08N140W. 
SCATTERED MODERATE ISOLATED STRONG CONVECTION IS N OF 06N TO THE 
COAST OF CENTRAL AMERICA BETWEEN 85W AND 91W. ISOLATED MODERATE 
TO STRONG CONVECTION IS OBSERVED N OF 11N BETWEEN 93W AND 97W. 
 
...DISCUSSION...
ALOFT...AN UPPER ANTICYCLONE CENTERED W OF AREA EXTENDS A RIDGE 
NE ACROSS THE FORECAST WATERS FROM 13N140W TO 27N118W. STRONG 
SWLY WINDS OF 50-60 KT ARE TRANSPORTING ABUNDANT MID TO UPPER 
LEVEL MOISTURE ACROSS THE NW CORNER OF THE AREA. THESE WINDS ARE 
ASSOCIATED WITH A CUT-OFF LOW LOCATED NEAR 25N145W. AN UPPER 
LEVEL LOW IS NEAR 15N126W. AN INVERTED TROUGH EXTENDS FROM 
22N120W TO LOW CENTER THEN SSE TO THE EQUATOR AT 122W. E OF THIS 
TROUGH...ANOTHER RIDGE DOMINATES THE FORECAST WATERS PRODUCING A 
LOW SHEAR ENVIRONMENT AND GOOD OUTFLOW OVER T.D. THIRTEEN. 
ANOTHER INVERTED TROUGH IS SEEN ALONG 90W N OF 5N. NE FLOW ALOFT 
IS NOTED W OF THIS TROUGH.  

AT LOW LEVELS...A 1025 MB HIGH PRES CENTERED N OF AREA NEAR 
35N136W EXTENDS A RIDGE ACROSS THE N WATERS TO NEAR 23N120W. AN 
AREA OF FRESH TRADE WINDS IS SEEN ON THE SOUTHERN PERIPHERY OF 
THE RIDGE FROM 10N TO 20N W OF 130W. SCATTEROMETER PASSES 
CONFIRMED THE PRESENCE OF THESE WIND SPEEDS. TRADES WILL 
DIMINISH TO 20 KT OR LESS IN ABOUT 24 HOURS AS HIGH PRES 
SLIGHTLY WEAKENS AND A COLD FRONT APPROACHES FROM THE NW. THE 
FRONT IS FORECAST TO DISSIPATE BEFORE REACHING THE FORECAST 
WATERS. HOWEVER...A SWELL EVENT IN THE WAKE OF THE FRONT IS 
EXPECTED TO IMPACT THE NW WATERS SUN AND MON...BUILDING SEAS TO 
AROUND 11 FT. EXPECT NW SWELLS WITH PERIODS OF 18 TO 20 SECONDS 
AT THE LEADING EDGE OF THE SWELL TRAIN. THESE SWELLS WILL 
PROPAGATE ACROSS THE FORECAST WATERS REACHING THE WATERS NW OF A 
LINE FROM 29N130W TO 20N139W SUN NIGHT. 

GAP WINDS...RIDGE ACROSS EASTERN MEXICO AND THE SW GULF OF 
MEXICO IS SUPPORTING A GAP WIND EVENT THROUGH THE GULF OF 
TEHUANTEPEC. THE MOST RECENT ASCAT PASS PROVIDED OBSERVATIONS OF 
20-25 KT WINDS ACROSS THE GAP REGION. THIS WEATHER PATTERN IS 
FORECAST TO PERSIST OVER THE NEXT COUPLE OF DAYS WITH THE 
STRONGEST WINDS OCCURRING LATE AT NIGHT TILL THE EARLY MORNING 
HOURS. 

$$
GR