000
AXPZ20 KNHC 190948
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC FRI OCT 19 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 
0945 UTC.

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

THE MONSOON TROUGH EXTENDS E TO W ACROSS CENTRAL NICARAGUA TO 
THE COAST OF EL SALVADOR AT 14N88W...THEN DIPS SW TO ALONG 11N 
BETWEEN 101W AND 106W...THEN TURNS NW CRESTING ALONG 14N BETWEEN 
114W AND 121W WHERE LOW LEVEL WINDS INDICATE A TRANSITION TO AN 
ITCZ...WHICH CONTINUES SW TO BEYOND 09N140W. SCATTERED MODERATE 
ISOLATED STRONG CONVECTION IS NOTED WITHIN 120 NM EITHER SIDE OF 
A LINE FROM 09N84.5W TO 10.5N89W TO 11N99W...WITHIN 15 NM OF 
14.5N116W AND 10N134W...AND WITHIN 120 NM OF 09N140W. SMALL 
CLUSTERS OF DISSIPATING CONVECTION IS OBSERVED ALONG THE COAST 
OF EL SALVADOR AND ALONG THE PACIFIC COAST OF MEXICO AT 15.8N98W.

...DISCUSSION...

AN UPPER LEVEL ANTICYCLONE IS W OF THE AREA AT 31N146W WITH AN 
UNSTABLE UPPER RIDGE EXTENDING NE TO A CREST AT 36N135W WHICH IS 
COLLAPSING S OVER THE EXTREME NW PORTION OF THE DISCUSSION AREA. 
A VERY SMALL UPPER CYCLONE IS FILLING AT 24N140W WHILE SHIFTING 
SOUTHWARD. A MID TO UPPER CYCLONE IS CENTERED AT 27N122W WITH AN 
UPPER TROUGH EXTENDING S TO A BASE OVER THE DEEP TROPICS AT 
12N127W. SOME UPPER MOISTURE IS OBSERVED WITHIN 240 NM OVER THE 
N SEMICIRCLE OF THIS LARGE UPPER CYCLONE...OTHERWISE THE UPPER 
LEVELS APPEAR VERY DRY W OF THE UPPER TROUGH....ROUGHLY TO THE W 
AND NW OF A LINE FROM 32N115W TO 20N116W TO 13N140W. FURTHER S 
WEAK UPPER DIFFLUENCE IS INDICATED OVER THE CONVECTION 
ASSOCIATED WITH MONSOON TROUGH AND ITCZ ALL TO THE W OF 
116W...WITH THE DEBRIS MOISTURE EVAPORATING WITHIN A FEW 
HUNDRED MILES OF THE DISSIPATING CLUSTERS.      

THE EASTERN PORTION IS DOMINATED BY A UPPER ANTICYCLONE CENTERED 
OVER W-CENTRAL OLD MEXICO AT 21N103W WITH A RIDGE EXTENDING NW 
ALONG THE COAST OF MEXICO...AND CRESTING OVER SOUTHERN 
CALIFORNIA. UPPER MOISTURE IS NOTED ALONG THE RIDGE AXIS ACROSS 
THE BAJA PENINSULA...CONTINUING SE ACROSS NORTHERN MEXICO AND 
ACROSS THE W CENTRAL GULF OF MEXICO INTO ANOTHER UPPER TROUGH. 
THE ENVELOPE OF ANTICYCLONIC FLOW EXTENDS S OVER THE DISCUSSION 
AREA N OF 07N TO THE E OF 112W. THE UPPER EASTERLY FLOW IS 
ADVECTING DEBRIS MOISTURE FROM THE MONSOON TROUGH W ALONG 10-13N 
FROM CENTRAL AMERICA TO 110W...WHERE IT TURNS N BUT SEEMS TO 
EVAPORATE BEFORE REACHING THE SOUTHERN BAJA PENINSULA.   

ELSEWHERE AT THE SURFACE...A 1011 MB SURFACE LOW IS NEAR 30N125W 
TRAILING A LOW LEVEL TROUGH S TO 20N125W. BROKEN-OVERCAST 
STRATOCUMULUS IS OBSERVED WITHIN 360 NM NW OF THE TROUGH. 
NORTHERLY 15-20 KT WINDS ARE CURRENTLY OBSERVED TO THE N OF 27N 
BETWEEN 125W AND 136W...WITH SEAS 7-9 FT PRIMARILY DUE TO MIXING 
NE AND NW SWELL. THIS AREA OF ENHANCED N WINDS WILL SHIFT TO NW 
OF A LINE FROM 30N132W TO 23N140W ON SAT...THEN GRADUALLY 
DIMINISH SAT NIGHT. EXPECT BROAD LOW LEVEL TROUGHING TO CONTINUE 
OVER THE AREA FROM 20N-28N BETWEEN 117W-127W THROUGH LATE SAT 
EFFECTIVELY SEPARATING NORTHERLY LOW LEVEL FLOW WHICH WILL FILL 
IN ACROSS THE ENTIRE AREA N OF 17N W OF 106W BY MIDDAY ON SUN. 
SEAS OF 3-5 FT IN NW SWELL ARE EXPECTED ALONG THE ENTIRE PACIFIC 
COAST OF THE BAJA CALIFORNIA PENINSULA THROUGH MIDDAY MON...THEN 
GUIDANCE SUGGESTS SEAS WILL BUILD SLIGHTLY TO 5-6 FT N OF 28N 
ALONG THE W SHORE OF PENINSULA MON NIGHT. SEAS OF 1-3 FT 
EXPECTED ACROSS THE ENTIRE GULF OF CALIFORNIA THROUGH LATE 
MON...THEN GUIDANCE SUGGESTS A SLIGHT INCREASE TO 3-4 FT IN 
REFRACTIVE SWELL OVER THE GULF WATERS TO THE S OF 24.5N 
BEGINNING MON NIGHT.   
  
GAP WINDS...EXPECTING A NORTHERLY SURGE AT 20-25 KT IN THE GULF 
OF TEHUANTEPEC BEGINNING LATE FRI NIGHT...THEN PULSING WELL INTO 
NEXT WEEK WITH THE STRONGEST DRAINAGE FLOW OCCURRING LATE EACH 
NIGHT TILL JUST AFTER SUNRISE EACH MORNING. GFS GUIDANCE IS 
SUGGESTING THIS NORTHERLY FLOW WILL HELP TRIGGER LOW PRESSURE 
DEVELOPMENT WITHIN THE MONSOON TROUGH NEAR 11N95W EARLY NEXT 
WEEK. ALTHOUGH THERE IS A HINT OF THE DEVELOPMENT IN OTHER 
GUIDANCE...THE GFS IS MUCH MORE AGGRESSIVE AND THUS IS TONED 
DOWN CONSIDERABLY IN THE EXPERIMENTAL GRIDDED FIELDS.   

$$
NELSON