000
AXPZ20 KNHC 211526
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SUN OCT 21 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1545 UTC.

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

MONSOON TROUGH EXTENDS FROM 11N86W TO 12N95W TO 11N110W TO 
08N125W TO 10N133W. ITCZ AXIS EXTENDS FROM 10N133W TO 10N140W. 
SCATTERED MODERATE ISOLATED STRONG WITHIN 60 NM EITHER SIDE OF 
TROUGH AXIS E OF 90W...WITHIN 150 NM EITHER SIDE OF AXIS BETWEEN 
91W AND 100W...AND 120 NM EITHER SIDE OF AXIS BETWEEN 110W AND 
124W. 

...DISCUSSION...

SIGNIFICANT CHANGES IN THE UPPER LEVEL PATTERN FROM 24 HOURS 
AGO. UPPER LEVEL ANTICYCLONE CENTERED WELL OF THE AREA HAS 
RETROGRADED AND CONSOLIDATED NEAR 13N163W. THE TWO LARGE UPPER 
LEVEL CYCLONES DOMINATING THE SUBTROPICS W OF 118W HAVE SPLIT 
FURTHER APART WITH CENTERS ONE CENTER NEAR 31N114W MOVING NE 
INTO THE ARIZONA...AND THE OTHER CENTER NEAR 20N150W PULLING 
WESTWARD TOWARD HAWAII. AXIS OF SUBTROPICAL JET EXTENDS FROM 
15N145W AND CUTS NE ACROSS THE AREA NEAR 20N140W THEN SPILLS 
EASTWARD TO SOUTHERN BAJA CALIFORNIA. SATELLITE DERIVED WINDS
WERE IN THE 90-100 KT RANGE. THIS JET WAS ADVECTING SOME 
UPPER LEVEL MOISTURE OVER THE AREA FROM 10N TO 24N BETWEEN 130W 
AND 140W. OTHERWISE THE UPPER LEVELS APPEAR VERY DRY N OF 10N W 
OF 115W AND SUPPRESSING CONVECTION. AN UPPER CYCLONE IS OVER THE 
DEEP TROPICS NEAR 02N130W SETTING UP AN AREA OF WEAK UPPER 
DIFFLUENCE OVER THE WESTERN SEGMENT OF THE MONSOON TROUGH AND 
ITCZ...AND SUPPORTING THE CONVECTION PREVIOUSLY DESCRIBED 
BETWEEN 110W AND 124W. 
     
THE EASTERN PORTION OF THE DISCUSSION IS DOMINATED BY A 
QUASI-STATIONARY ELONGATED UPPER ANTICYCLONE OVER CENTRAL OLD 
MEXICO NEAR 19N99W WITH A RIDGE EXTENDING NWD TO A CREST OVER 
TEXAS. THE ENVELOPE OF ANTICYCLONIC FLOW EXTENDS S OVER THE 
DISCUSSION AREA N OF 07N TO THE E OF 115W. THE UPPER EASTERLY 
FLOW IS ADVECTING DEBRIS MOISTURE FROM THE MONSOON TROUGH 
CONVECTION NOTED BETWEEN 91W AND 100W WESTWARD BETWEEN 07N-13N 
FROM CENTRAL AMERICA TO 105W.     

A BROAD SURFACE RIDGE COVERS THE SUBTROPICS N OF THE MONSOON 
TROUGH AND A SURFACE TROUGH EXTENDING FROM 15N127W TO 11N133W. 
SCATTEROMETER DATA INDICATED SUB NORMAL TRADE WINDS OF 10-15 KT 
N OF THE MONSOON TROUGH W OF 120W. 
  
GAP WINDS...
A 0500 UTC HIGH RESOLUTION OSCAT PASS INDICATED N TO NNE WINDS 
OF 20-25 KT WINDS PULSING IN THE GULF OF TEHUANTEPEC. THESE 
WINDS ARE EXPECTED TO PULSE THROUGH THE NEXT 48 HOURS WITH THE 
STRONGEST DRAINAGE FLOW OCCURRING LATE EACH NIGHT TILL JUST 
AFTER SUNRISE EACH MORNING. ONCE AGAIN THE GFS NWP GUIDANCE 
CONTINUES TO SUGGEST THIS NORTHERLY FLOW WILL HELP TRIGGER LOW 
PRESSURE DEVELOPMENT WITHIN THE MONSOON TROUGH NEAR 11N100W BY 
TUE. THE GFS REMAINS THE AGGRESSIVE OUTLIER IN ITS SOLUTION 
WHILE OTHER NWP MODELS FAVOR A WEAKER BROAD LOW CLOSER TO 
CENTRAL AMERICA WHICH DRIFTS TO THE EAST AS DEVELOPING TROPICAL 
CYCLONE IN THE CARIBBEAN EXERTS GREATER INFLUENCE ON THE OVERALL 
PATTERN. THIS SOLUTION IS FAVORED AT THIS TIME AND LOW PRES IS 
NOT REFLECTED IN FORECAST WIND WAVE CHARTS THROUGH 72 HOURS AND 
THE GRIDDED WIND FIELDS. 

$$
COBB