000
AXPZ20 KNHC 030943
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC WED OCT 03 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 
0900 UTC.

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

THE MONSOON TROUGH IS ALONG 08N78W TO 11N90W TO 11N105W TO 
10N124W TO 08N133W. THE INTERTROPICAL CONVERGENCE ZONE AXIS 
EXTENDS FROM 08N133W TO 08N140W. SCATTERED MODERATE AND ISOLATED 
STRONG CONVECTION IS N OF 12N BETWEEN 92W AND 97W. SCATTERED 
MODERATE CONVECTION IS WITHIN 60-90 NM EITHER SIDE OF A LINE 
FROM 11N100W TO 09N106W TO 09N112W TO 10N119W. SIMILAR 
CONVECTION IS WITHIN 150 NM N OF THE ITCZ BETWEEN 130W AND 133W.

...DISCUSSION...

AN UPPER LEVEL CYCLONE IS CENTERED AT 33N136W WITH AN UPPER 
TROUGH EXTENDING S AND SE THROUGH 27N132W TO A BASE OVER THE 
DEEP TROPICS AT 13N132W. AN EXPANSIVE UPPER ANTICYCLONE IS 
POSITIONED AT 22N115W WITH A RIDGE EXTENDING N BEYOND 32N119W 
TOWARD CAPE MENDOCINO CALIFORNIA. A SECOND UPPER RIDGE EXTENDS 
SW TO A CREST OVER THE TROPICS TO 11N130W. WEAK UPPER DIFFLUENCE 
IS NOTED OVER THE DEEP TROPICS S AND E OF THE UPPER RIDGING 
SUPPORTING CONVECTION ALONG THE MONSOON TROUGH AS IS DESCRIBED 
ABOVE. RESULTANT DEBRIS MOISTURE FANS OUT BOTH TO THE N AND TO 
THE S BUT SEEMS TO EVAPORATE WITHIN 180 NM OF THE CLUSTERS AS 
THE UPPER LEVELS ARE VERY DRY OVER THE MAJORITY OF THE 
DISCUSSION AREA N OF 15N W OF 107W. 

AN UPPER CYCLONE OVER THE TEXAS/LOUISIANA BORDER HAS AN UPPER 
TROUGH EXTENDING SW ACROSS THE WESTERN GULF OF MEXICO REACHING 
ACROSS CENTRAL MEXICO TO A BASE IN THE NE PACIFIC AT 16N105W. AN 
UPPER RIDGE EXTENDS NW FROM S AMERICA ACROSS THE DEEP TROPICS TO 
THE S OF 10N E OF 90W AND IS ADVECTING UPPER MOISTURE W ACROSS 
THE DISCUSSION AREA E OF 90W. ADDITIONAL MOISTURE IS SPREADING 
NE ACROSS CENTRAL AMERICA AND THE SE GULF OF MEXICO.

ELSEWHERE AT THE LOW LEVELS...A BROAD SURFACE RIDGE COVERS THE 
AREA N OF 20N W OF 120W. THE NEARLY STATIONARY REMNANT TROUGH OF 
MIRIAM EXTENDS FROM 19N117W TO 12N117W WITH ONLY LIGHT TO 
MODERATE WINDS IN ITS VICINITY AS SEEN BY OVERNIGHT 
SCATTEROMETER PASSES.

SW LOW LEVEL WINDS AT 15 TO 20 KT ALONG WITH CROSS EQUATORIAL SW 
SWELL CONTINUES TO RESULT IN SEAS TO 9 FT S OF 10N BETWEEN 100W 
AND 120W. THE WINDS ARE EXPECTED TO DIMINISH TO 15 KT WITHIN 24 
TO 48 HOURS...AND THE AREA OF SW SWELL WILL GRADUALLY DECAY TO 
THE 8 FT MARK WHILE RETREATING TO 04N BY 48 HOURS.

GAP WINDS...HIGH PRES IS BUILDING IN ACROSS EASTERN MEXICO IN 
THE WAKE OF A COLD FRONT THAT MOVED THROUGH THE WESTERN GULF OF 
MEXICO THE PAST COUPLE OF DAYS AND HAS NOW STALLED OUT OVER THE 
YUCATAN. THIS HAS USHERED IN A SURGE OF NORTHERLY WINDS THROUGH 
THE CHIVELA PASS TO THE GULF OF TEHUANTEPEC. A FEW SUCCESSIVE 
OBSERVATIONS FROM A SHIP THAT MOVED RIGHT THROUGH THE GULF OF 
TEHUANTEPEC MEASURED WINDS OF 40 TO 52 KT AT AN ANEMOMETER 
HEIGHT OF 36 METERS. MEANWHILE A 0412 UTC ASCAT PASS INDICATED 
AN AREA OF 30 KT WINDS. GIVEN THE LOW BIAS OF THE ASCAT AND THE 
CONVERTED WIND SPEED OF THE SHIP OBSERVATIONS ISSUED A GALE 
WARNING FOR THE GULF OF TEHUANTEPEC FROM 06 UTC THROUGH 18 UTC 
TODAY. GLOBAL MODEL GUIDANCE FROM THE GFS...ECMWF AND UKMET ALL 
SHOWED AN AREA OF 30 KT WINDS IN THIS VICINITY WHILE THE 35 KM 
GFS DID SHOW 35 KT IN A SMALL AREA. WINDS OF 20 TO 30 KT WILL 
SPILL OUT OF THIS AREA AND DOWNWIND PERSISTING THROUGH AT LEAST 
THE NEXT 48 HOURS AS THE PRES GRADIENT REMAINS TIGHT WITH HIGH 
PRES ANCHORED OVER MEXICO.

IN THE GULF OF PAPAGAYO...NE TO E WINDS ARE FORECAST TO INCREASE 
TO 20 TO 25 KT IN 24 HOURS AS TRADES E OF CENTRAL AMERICA IN THE 
CARIBBEAN SEA SPREAD WESTWARD. THESE WINDS ARE FORECAST TO THEN 
DIMINISH BY 48 HOURS AS THE TRADES BACK OFF.

$$
LEWITSKY