000
AXPZ20 KNHC 081533
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC THU SEP 08 2011

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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1515 UTC.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH IS ALONG 16N101W TO 18N109W TO 11N117W TO 
13N130W TO 08N140W. SCATTERED MODERATE AND ISOLATED STRONG 
CONVECTION IS WITHIN 180 NM OF THE AXIS E OF 120W.

...DISCUSSION...
ALOFT...A STRONG LONGWAVE TROUGH IS ACROSS THE NORTH-CENTRAL 
PACIFIC N OF 30N ALONG ABOUT 159W. TWO SHORTWAVES LIE TO THE SE 
OF THIS TROUGH EMBEDDED IN SOUTHWESTERLY FLOW ON SE PERIPHERY OF 
THE TROUGHING. THE FIRST SHORTWAVE CONTINUES TO ELONGATE AND 
STRETCH N OF THE HAWAIIAN ISLANDS NEAR 30N154W...WHILE A SECOND 
SHORTWAVE WAS WELL NORTH OF THE DISCUSSION AREA NEAR 
40N134W...BOTH OF THEM MOVING NE. THESE CYCLONES ARE FORECAST TO 
CONTINUE LIFTING TO THE NE OVER A RIDGE ENCOMPASSING MUCH OF THE 
NORTHWESTERN DISCUSSION AREA TO THE SE DURING THE NEXT FEW DAYS. 
TWO ANTICYCLONIC CIRCULATIONS...ONE CENTERED NEAR 25N107W...AND 
THE OTHER WITH MEAN CENTER NEAR 25N132W ARE FORMING THE MAKEUP 
OF THIS PERSISTENT RIDGING. DRY AND STABLE AIR UNDER MODERATE TO 
STRONG SUBSIDENCE ACCOMPANIES THE RIDGE N OF 18N W OF 105W. 
WEDGED IN BETWEEN THESE TWO HIGHS WAS A WEAKENING MID LEVEL 
CYCLONE NEAR 23N122W SHIFTING SLOWLY WESTWARD. A CHANGE IN THE 
UPPER PATTERN WILL BE REALIZED BY FRI AS THE EASTERN MOST 
ANTICYCLONE COLLAPSES AND SINKS SW...AND THE WESTERN ANTICYCLONE 
SHIFTS W TO ALONG 137W. THIS WILL ALLOW BROAD UPPER LEVEL 
TROUGHING TO ENCOMPASS ALL OF NORTH AMERICA N OF 27N. NE TO E 
FLOW ALOFT PERSISTS S OF THE PRESENT RIDGE ACROSS MUCH OF THE 
REMAINDER OF THE DISCUSSION AREA AND IS MAINTAINING A MODESTLY 
SHEARED UPPER LEVEL ENVIRONMENT CONDUCIVE FOR CONVECTION. 

AT THE SURFACE...A BROAD RIDGE OF HIGH PRES COVERS THE AREA N OF 
17N W OF 115W....CENTERED BY A 1025 MB HIGH NEAR 41N132W. WHILE 
A WEAK PRESSURE GRADIENT REMAINS IN PLACE...TRADES REMAIN LESS 
THAN 20 KT ACROSS THE NE PACIFIC WATERS. AN AREA OF 20 TO 25 KT 
S TO SW WINDS EXISTS FROM 08N TO 13N BETWEEN 108W AND 118W WITH 
SEAS TO 12 FT. THIS BROAD AREA OF WINDS WILL CONTINUE TO PRODUCE 
AN ELONGATED ZONE OF ACTIVE TSTMS WITH AREAS OF HEAVY RAIN 
THROUGH THU...AND WILL THEN GRADUALLY EXPAND AND ENCOMPASS THE 
AREA FROM 10N TO 18N BETWEEN 102W AND 120W IN 24 HOURS. ALSO OF 
NOTE...WITH STRONG NORTHERLY WINDS EXPECTED ACROSS PORTIONS OF 
THE SOUTHWESTERN GULF OF MEXICO DUE TO TROPICAL STORM NATE...20 
TO 25 KT N WINDS ARE EXPECTED TO FUNNEL THROUGH THE CHIVELA PASS 
AND INTO THE GULF OF TEHUANTEPEC REGION THROUGH 48 HOURS BEFORE 
NATE BEGINS TO MOVE N-NW AND AWAY FROM THE REGION. 

MARINE CONDITIONS ACROSS THE AREA ARE OTHERWISE DOMINATED BY 
FADING SOUTHERN HEMISPHERE SW SWELL THAT HAS BEGIN TO MIX WITH 
SE SWELL GENERATED ACROSS THE SE PACIFIC. THIS SE SWELL WILL 
CONTINUE TO MOVE THROUGH THE AREA WATERS THROUGH SAT...WHILE A 
NEW PULSE OF SW SWELL ENTERS THE AREA EARLY SAT.

$$
HUFFMAN