000
AXPZ20 KNHC 220952
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL 
1005 UTC SUN SEP 22 2013

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 
0930 UTC.

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

THE MONSOON TROUGH AXIS EXTENDS FROM 13N98W TO 10N115W TO 
10N120W TO 11N137W...THEN TRANSITIONS TO THE ICTZ TO 10N140W. 
SCATTERED MODERATE CONVECTION IS WITHIN 60 NM S OF TROUGH 
BETWEEN 115W-119W.

...DISCUSSION...

W OF 110W...                                             
SATELLITE WATER VAPOR IMAGERY SHOWS MODERATE TO STRONG 
SUBSIDENCE OVER JUST ABOUT THIS PORTION OF THE DISCUSSION AREA  
AS A LARGE ANTICYCLONE THAT HAS SHIFTED EASTWARD OVER THE PAST 
FEW DAYS TO NEAR 24N115W CONTINUES TO BE THE MAIN FEATURE THAT 
DOMINATES HERE. THE RESULTANT DRY AND STABLE CONDITIONS ARE EVEN 
LIMITING CONVECTION FROM DEVELOPING IN THE TROPICAL REGION.  
WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS ARE NOTED WITHIN 
ABOUT 45-60 NM OF THE MONSOON TROUGH W OF 120W. PATCHES OF 
BROKEN STRATOCUMLUS CLOUDS ARE N OF 17N BETWEEN 113W-127W. ONLY 
ISOLATED SHOWERS ARE NOTED ELSEWHERE S OF 16N.

A RATHER STRONG EARLY SEASON DEEP LAYER TROUGH MOVED INLAND 
CALIFORNIA YESTERDAY...AND IS CURRENTLY PRESSING EASTWARD OVER 
THE WESTERN U.S. THE TROUGH STRETCHES SW THROUGH 32N122W TO 
28N130W...AND TO AN UPPER LOW DRIFTING WWD W OF THE AREA AT 
26N146W. THE ASSOCIATED SURFACE COLD FRONT IS RAPIDLY WEAKENING 
FROM FAR NW BAJA CALIFORNIA SW TO 26N125W WHERE IT BECOMES 
FRAGMENTED TO 25N140W. ONLY ISOLATED SHOWERS ARE WITHIN 30 NM OF 
THE FRONT. ELSEWHERE AT THE SURFACE...GENERALLY A WEAK PRES 
PATTERN REMAINS AS REVEALED IN LATEST ASCAT DATA...EXCEPT IN THE 
FAR NE PORTION N OF 27N E OF 119W WHERE A RECENT ASCAT PASS 
HIGHLIGHTED NW WINDS OF 2O KT. 
 
THE DEEP LAYER TROUGH WILL CONTINUE TO ADVANCE EASTWARD OVER THE 
WESTERN U.S TODAY WITH BROAD SCALE RIDGING IN THE WAKE TROUGH 
RELATED TO AN UPPER ANTICYCLONE LOCATED ABOUT 600 NM NE OF THE 
UPPER LOW AT 26N146W SHIFTING EASTWARD TO COVER THE NRN HALF OF 
THE AREA INTO TUE. THIS PROCESS WILL FORCE THE UPPER LOW FARTHER 
W TO NNE OF THE HAWAII BY TUE. THE COLD FRONT IS FORECAST TO  
DISSIPATE BY THIS EVENING. WINDS N OF THE FRONT ARE FORECAST TO 
BE NLY AT 10-15 KT. SEAS TO 9 FT IN A NW SWELL COMPONENT ARE 
FORECAST BY WAVEWATCH GUIDANCE TO FOLLOW IN BEHIND THE FRONT TO 
N OF 28N E OF 126W BY THIS EVENING...AND THEN BE CONFINED TO N 
OF 29N BETWEEN 119W AND 123W BY EARLY MON EVENING BEFORE THEY 
SUBSIDE TO LESS THAN 8 FT OVERNIGHT ON MON.
 
THE SURFACE HIGH PRES RIDGING BUILDING EASTWARD ACROSS THE ABOVE 
COLD FRONT IS COMBINING WITH TROUGHING JUST INLAND NW MEXICO TO 
INDUCE THE 20 KT NW WINDS IN THE NE PORTION AS MENTIONED ABOVE. 
SEAS THERE ARE 6-8 FT. THESE CONDITIONS ARE FORECAST TO DIMINISH 
AS THE RIDGE WEAKENS SOME IN RESPONSE TO ANOTHER COLD FRONT THAT 
NEARS THE FAR N CENTRAL AND NW WATERS DURING MON AND TUE. MODEL 
GUIDANCE IS IN CONSENSUS THAT THIS NEXT FRONT WILL ALSO QUICKLY 
WEAKEN LATE MON INTO TUE AS STRONGER HIGH PRES SITUATED NW OF 
THE AREA BEGINS TO BUILD SE ACROSS THE N CENTRAL AND NW 
PORTIONS. THE LEADING EDGE OF A NEW SET OF NW SWELLS IS FORECAST
TO BEGIN TO PROPAGATE INTO THE FAR NORTHERN WATERS ON TUE WITH
WAVEWATCH GUIDANCE SUGGESTING SEAS BUILDING TO 9 OR 10 FT THERE.

POTENTIAL VORTICITY GUIDANCE SUGGESTS THAT THE TAIL-END OF THE 
ABOVE MENTIONED UPPER TROUGH WILL GRADUALLY DROP S AND INTERACT 
TO SOME EXTENT WITH MONSOON TROUGH SW FLOW AND RELATED MOISTURE 
TO SPIN UP LOW PRES NEAR 120W DURING THE EARLY TO MIDDLE PART OF 
THE UPCOMING WEEK. MODELS TEND TO AGREE...FOR THE MOST PART...ON 
SUCH A FEATURE THAT LIFTS NE DURING THAT TIME. FOR NOW WILL 
DEPICT THIS FEATURE AS A 1008 MB LOW ALONG THE MONSOON TROUGH ON 
THE MANUAL GRAPHICS VALID AT 48 AND 72 HOURS FROM 00 UTC LAST 
NIGHT. 

E OF 110W...                                                 
DEEP ATMOSPHERIC MOISTURE IS EVIDENT OVER THIS PORTION OF THE 
AREA AS THE CIRCULATION AROUND AN E TO W UPPER LEVEL RIDGE 
ACROSS CENTRAL MEXICO TIED TO THE ANTICYCLONE AT 14N115W 
CONTINUES TO DRIVE MOISTURE DERIVED FROM INCREASED CONVECTION 
OCCURRING UNDER A REGION OF UPPER LEVEL DIFFLUENCE OVER SOUTHERN 
MEXICO W TO 110W. A MID TO UPPER LEVEL INVERTED TROUGH IN THE 
EASTERLY FLOW S OF THE UPPER LEVEL RIDGE HAS MOVED W TO ALONG 
107W N OF 07N. ISOLATED SHOWERS AND TSTMS ARE WITHIN 120 NM E OF 
THE TROUGH. ACTIVE CONVECTION IS NOTED TO THE SE OF THE TROUGH 
IN THE FORM OF SCATTERED STRONG INTENSITY FROM 08N TO 10N 
BETWEEN 86W AND 90W...AND SCATTERED MODERATE/ISOLATED STRONG 
CONVECTION IS WITHIN 60 NM OF LINE FROM 09N94W TO 09N100W TO 
09N105W. SIMILAR CONVECTION IS WITHIN 60-75 NM OF THE COAST OF 
MEXICO BETWEEN PUERTO ANGEL AND MANZANILLO. THE OVERALL COVERAGE 
OF CONVECTION IN THE TROPICS REMAINS QUITE MINIMAL GIVEN THE 
TIME OF YEAR...BUT SHOULD INCREASE SOME BY THE MIDDLE PART OF 
THE UPCOMING WEEK AS A WEAK PRES PATTERN AND RELATIVELY LOW PRES 
MAINLY WITH THE MONSOON TROUGH TAKE PRECEDENCE HERE. AN AREA OF 
SW 15-20 KT WINDS WITH SEAS TO 8 FT IN A SW SWELL COMPONENT FROM 
06N TO 08N BETWEEN 97W AND 105W IS FORECAST TO DIMINISH MON 
EVENING. ELSEWHERE LITTLE CHANGES IN CURRENT OBSERVED MARINE 
CONDITIONS ARE EXPECTED THROUGH THE NEXT 48 HOURS.

$$
AGUIRRE