000
AXPZ20 KNHC 042158
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC TUE OCT 04 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2145 UTC.
 
...ITCZ/MONSOON TROUGH...

MONSOON TROUGH AXIS EXTENDS FROM 10N86W TO 12.5N94W TO 12N102W 
TO 1009 MB LOWS AT 121N112W AND AT 10N120W...THEN CONTINUES
TO 10N130W TO 8N138W WHERE LOW LEVEL WINDS INDICATE THAT THE 
ITCZ AXIS BEGINS AND EXTENDS TO BEYOND 7N140W. SCATTERED 
MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 45 NM OF THE 
TROUGH BETWEEN 94W-96W...BETWEEN 103W-107W...AND WITHIN 120 NM N 
OF THE TROUGH BETWEEN 114W-116W. SIMILAR CONVECTIVE ACTIVITY 
ATTRIBUTE TO LOW LEVEL WIND SPEED CONVERGENCE S OF THE TROUGH IS 
WITHIN 60 NM OF A LINE FROM 7N95W TO 9N100W TO 10N105W. 
SCATTERED MODERATE CONVECTION IS N OF THE TROUGH WITHIN 30 NM OF 
LINE 13N119W 11N123W...AND S OF THE TROUGH WITHIN 30 NM OF 
10N115W.

...DISCUSSION...

...N OF 18N... 

THE BROAD SCALE ATMOSPHERIC PATTERN REMAINS RATHER PROGRESSIVE 
TO THE N OF THE DISCUSSION AREA. A RATHER SHARP DEEP LAYER TROUGH
WITHIN THIS FLOW PATTERN IS HAS MOVED INLAND THE WESTERN U.S. AS
VERY AMPLIFIED RIDGE WELL TO THE W OF THE REGION ADVANCES 
EASTWARD. THE TAIL END OF THE TROUGH IS FORECAST TO SHEAR OFF 
AND DEVELOP INTO A CYCLONIC CIRCULATION THAT MOVES WESTWARD TO 
NEAR 19N140W TONIGHT AND TO W OF THE AREA NEAR 19N144W BY LATE 
WED. AT THE SURFACE A DISSIPATING FRONTAL TROUGH ASSOCIATED WITH 
THE TROUGH IS MOVING INLAND SOUTHERN CALIFORNIA...AND STRETCHES 
FROM 32N117W SW TO 27N121W. SCATTERED TO BROKEN LOW CLOUDS WITH 
ISOLATED SHOWERS ARE WITHIN 30 NM EITHER SIDE OF THE FRONT. IN
THE WAKE OF THE FRONT...A HIGH PRES RIDGE IS BUILDING E ALONG 
27N. HIGH PRES COVERS THE AREA N OF 18N AND W OF 120W.

THE FRONTAL TROUGH IS FORECAST TO WASH OUT WITHIN THEN NEXT 
12-18 HRS AS IT LOSES ITS UPPER SUPPORT. W OF THE TROUGH WINDS
ARE LESS THAN 20 KT WITH SEAS TO 9 FT IN A NW SWELL COMPONENT.
THESE SEAS ARE FORECAST TO SUBSIDE TO LESS THAN 8 FT IN ABOUT 
30 HRS. BY LATE WED NIGHT INTO EARLY THU...ANOTHER DEEP LAYER 
TROUGH WILL SWING EASTWARD TO INLAND THE U.S. W COAST. THIS 
TROUGH
WILL PUSH A SURFACE COLD FRONT TO ALONG A LINE FROM 30N116W TO 
28N125W BY EARLY THU...AND FROM 30N115W TO 27N120W BY THU 
AFTERNOON. SEAS OF 8-10 FT WITH A MIXED SW AND NW SWELL COMPONENT
ARE FORECAST N OF 26N AND W OF 120 BY THU AFTERNOON.

...S OF 18N...

UPPER ANTICYCLONIC FLOW...MOSTLY INDUCED BY MONSOON CONVECTION 
...DOMINATES THIS AREA OF THE REGION. THE MID/UPPER LEVEL RIDGE 
EXTENDS E TO W FROM AN ELONGATED ANTICYCLONE OVER CENTRAL AMERICA
WESTWARD ALONG 16N TO 115W...THEN SOUTHWESTWARD TO A COL REGION 
AT 13N137W. ANOTHER MID/UPPER RIDGE EXTENDS NORTHWESTWARD FROM 
THE COL REGION TO AN ANTICYCLONE WELL W OF THE DISCUSSION AREA.

ABUNDANT DEEP LEVEL ATMOSPHERIC ALONG AND NEAR THE MONSOON TROUGH
IS FURTHER AIDED BY DIFFLUENCE OVER AND NEAR THE MID/UPPER RIDGE.
DEBRIS CLOUDINESS FROM THE ABOVE DESCRIBED CONVECTION SPREADS S 
TO NEAR 5N BEFORE IT DISSIPATES IN DRY AIR...WHILE TO THE N OF 
THE MONSOON TROUGH IT IS SPREADS NE TOWARDS MEXICO BEFORE IT TOO 
EVAPORATES AS IT ENCOUNTERS DRY AIR ALOFT.

A TIGHT PRES GRADIENT OVER MEXICO PRIMARILY DUE TO STRONG HIGH 
PRES OVER THE GULF OF MEXICO CONTINUES TO ALLOW FOR N-NE WINDS 
OF 20-30 KT WITH HIGHER GUSTS TO FUNNEL INTO THE GULF OF 
TEHUANTEPEC WITHIN 90 NM EITHER SIDE OF A LINE FROM 16N95W TO
14N96W TO 13N98W WITH SEAS 8-12 FT. THE GRADIENT IS EXPECTED TO 
WEAKEN JUST ENOUGH TO ALLOW FOR THESE WINDS TO WEAKEN TO 20-25 
KT IN 24 HRS AND TO 20 KT WITHIN 30 NM EITHER SIDE OF A LINE THAT
INCLUDES THE GULF OF TEHUANTEPEC FROM 16N95W TO 15N95W TO 14N96W
BY 48 HOURS WITH SEAS SUBSIDING TO 9 FT IN 24 HRS AND TO 8 FT IN
48 HRS.

FURTHER DOWNSTREAM FROM THE GULF OF TEHUANTEPEC...THE N-NE
WINDS BECOME MORE NE-E AND DIMINISH TO 20 KT AS THEY CONTINUE TO 
IMPINGE INTO THE MONSOON TROUGH WITH SEAS OF 8-10 FT. THIS 
PROLONGED NE FLOW INTO THE MONSOON TROUGH HAS HELPED INDUCED A 
1009 MB LOW NEAR 12N112W AS IT COMES INTO CONFLUENCE WITH SW 
FLOW OF 20 KT FROM 7N-10N BETWEEN 110W-116W. THE LOW IS PART OF
A BROAD ENVELOP OF MONSOONAL WIND FLOW WITH THE POSSIBILITY OF
ANOTHER LOW DEVELOPING TO ITS E DURING THE NEXT 48 HRS. PRESENTLY
20 KT WINDS ARE WITHIN 180 NM IN THE NE QUADRANT OF THE LOW WITH
SEAS LESS THAN 8 FT. THE LOW IS FORECAST TO REACH TO NEAR 11N116W
IN 24 HRS WITH S-SW WINDS OF 20-25 KT...AND SEAS OF 8-10 FT IN A 
SW SWELL FROM 6N-10N BETWEEN 100W-115W. BY 48 HRS...THE LOW 
SHOULD BE NEAR 11N120W AS A 1008 MB WITH 20 KT CONFINED TO 
WITHIN 120 NM OF THE LOW IN THE NW QUADRANT.

THE POSSIBILITY EXISTS FOR THE LOW TO PERHAPS GRADUALLY INTENSIFY
OVER THE NEXT 48 HRS AS SHEARED VORTICITY FROM THE ONGOING GULF 
OF TEHUANTEPEC EVENT IS ENTRAINED INTO IT. ELSEWHERE FROM 6N-10N 
BETWEEN 105W-114W S-SW WINDS OF 20-25 KT WITH SEAS OF 8-11 FT 
CAN BE EXPECTED IN 48 HRS.

A WEAK PRES PATTERN WILL REMAIN THROUGH THE NEXT COUPLE OF DAYS 
OVER THE REMAINDER OF REGION EXCEPT OVER THE FAR NORTHERN GULF 
OF CALIFORNIA WHERE A TIGHT PRES GRADIENT INDUCED BY LOW PRES 
OVER THE WESTERN U.S. AND HIGH PRES RIDGING OVER THE NORTHERN 
SECTION OF THE AREA IS ALLOWING FOR SW-W WINDS OF 20-25 KT TO 
THE N OF 29N. THESE WINDS ARE FORECAST TO CHANGE VERY LITTLE 
OVER THE NEXT 48 HRS AS THE GRADIENT THERE REMAINS ON THE TIGHT
SIDE.

SEAS TO 8 FT IN MERGING SW AND NW SWELLS ARE S OF 1N BETWEEN 
115W-126W. BY 24 HRS...EXPECT WINDS LESS THAN 20 KT WITH SEAS 
TO 8 OR 9 FT PRIMARILY IN A SW SWELL COMPONENT S OF 10N BETWEEN
98W-124W...AND REACHING N TO 14N BETWEEN 95W-117W BY 48 HRS.

$$
AGUIRRE