000
AXPZ20 KNHC 192154
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC MON SEP 19 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 
2115 UTC.

...SPECIAL FEATURE...

A 1009 MB LOW PRES CENTER ACROSS THE EPAC NEAR 12.5N 94.0W IS 
MOVING SLOWLY NW NEAR 5 KT. THIS SURFACE LOW PRES CENTER IS 
EMBEDDED WITHIN AN ELONGATED LOW TO MIDDLE LEVEL CYCLONIC 
CIRCULATION ALIGNED NE TO SW THAT IS SHIFTING WWD IN A WAVE LIKE 
FASHION. ABUNDANT TROPICAL MOISTURE IS ENTRAINED WITHIN THIS 
ELONGATED CIRCULATION AND IS PRODUCING SCATTERED TO NUMEROUS 
SHOWERS AND TSTMS FROM 10N TO THE PACIFIC COASTS BETWEEN 87W AND 
97W. ATMOSPHERIC AND OCEANIC CONDITIONS APPEAR FAVORABLE FOR 
THIS SYSTEM TO GRADUALLY BECOME BETTER ORGANIZED OVER THE NEXT 
FEW DAYS...AND GLOBAL MODELS SUGGEST A TROPICAL CYCLONE COULD 
DEVELOP FROM THIS AREA OF DISTURBED WEATHER BY THE END OF THE 
WEEK.    

...ITCZ/MONSOON TROUGH...

MONSOON TROUGH 09N78W TO LOW PRES 13N94W TO 08N105W...THEN 
RESUMES FROM 17N116W TO 11N124W TO 10N140W. SCATTERED MODERATE 
ISOLATED STRONG WITHIN 180 NM EITHER SIDE OF LINE FROM 06N81W TO 
15N99W...WITHIN 120 NM LINE 06N101W TO 11N109W...WITHIN 15 NM 
LINE 17.5N105W TO 20N106.5W...AND WITHIN 90 NM LINE 16N118W TO 
11N125W.

...DISCUSSION... 

ALOFT...A NARROW UPPER LEVEL RIDGE SPANS THE AREA...CENTERED ON 
TWO ANTICYCLONES...ONE NEAR 22N112W AND EXTENDING E ACROSS 
CENTRAL MEXICO AND INTO THE S CENTRAL GULF OF MEXICO...AND A 
SECOND ANTICYCLONE NEAR 19N133W EXTENDING SW TO THE ITCZ S OF 
THE BIG ISLAND OF HAWAII. BROAD AND WEAK TROUGHING PREVAILS TO 
THE N OF THIS RIDGE FROM 28N TO 40N WITH A SERIES OF WEAK 
SHORTWAVES MOVING SLOWLY E-NE ACROSS MID LATITUDES. A TUTT AXIS 
LIES IMMEDIATELY S OF THE RIDGE...EXTENDING FROM THE YUCATAN 
PENINSULA W-SW ACROSS S CENTRAL MEXICO TO A WEAK MID LEVEL 
PERTURBATION NEAR 12N118W. THE PRES GRADIENT DUE S OF THE UPPER 
ANTICYCLONE NEAR 21N113W WAS PRODUCING A JET SEGMENT ALOFT TO 
AROUND 40 KT AND AIDING IN INDUCING A ZONE OF UPPER LEVEL 
DIVERGENCE FROM 115W TO 125W. ANTICYCLONIC FLOW ALOFT WAS 
OCCURRING S OF THE TUTT ACROSS CENTRAL AMERICA AND WAS PRODUCING 
A BROAD ZONE OF DIRECTIONAL DIVERGENCE ALOFT FROM THE PACIFIC 
COASTS OF CENTRAL AMERICA EXTENDING OUT SOME 360 NM TO THE SW. 
THIS UPPER LEVEL PATTERN WAS AIDING IN MAINTAINING ACTIVE 
CONVECTION FROM THE OFFSHORE PACIFIC WATERS OF SE MEXICO TO THE 
GULF OF PANAMA...INCLUDING THE LOW PRES SYSTEM MENTIONED ABOVE.

AT LOW LEVELS...A 1023 MB SURFACE HIGH WAS CENTERED NEAR 34N137W 
WITH MODEST RIDGING EXTENDING SE TO NEAR 22N112W. GENERALLY 
LIGHT TO MODERATE TRADEWINDS CONTINUE ACROSS THE AREA BASED ON 
AFTERNOON SCATTEROMETER PASSES...WITH 20 KT TRADES GENERALLY W 
OF 145W...EXCEPT JUST TO THE N OF THE MONSOON TROUGH W OF 
120W...WHERE A SERIES OF WEAK LOW PRES CENTERS ARE KEEPING THE 
PRES GRADIENT TIGHT ENOUGH TO SUPPORT A SMALL AREA OF 20 KT 
WINDS. THE SURFACE HIGH PRES WILL CONTINUE TO WEAKEN THROUGH 
WEDNESDAY AS A DEEP LAYER TROUGH WELL NW OF THE AREA DIGS 
EASTWARD THROUGH THE N CENTRAL PACIFIC. THE AREA OF FRESH TRADES 
W OF 120W N OF THE MONSOON TROUGH WILL SLOWLY DIMINISH AS A 
RESULT.

THE MONSOON TROUGH ACROSS THE EPAC REMAINS BROKEN INTO TWO 
SEGMENTS TODAY...WITH THE EASTERNMOST SEGMENT ANCHORED ON BROAD 
LOW PRES ACROSS COLOMBIA AND THE SW CARIBBEAN EXTENDING THROUGH 
THE DEVELOPING LOW PRES SE OF THE GULF OF TEHUANTEPEC SW TO 
106W...AND A SECOND SEGMENT ANCHORED ON A PERSISTENT CYCLONIC 
CIRCULATION MEANDERING SW OF THE S TIP OF BAJA CALIFORNIA. 
SATELLITE IMAGERY TODAY SUGGESTS SEVERAL SMALL CYCLONIC 
CIRCULATIONS EMBEDDED WITHIN THE W SEGMENT OF THE TROUGH...WITH 
THE MOST SIGNIFICANT A 1010 MB LOW PRES CENTER NEAR 10N134W. 
COMPUTER MODEL GUIDANCE INDICATE THAT THESE LOWS ALONG THE 
TROUGH WILL SLOWLY WEAKEN AND DRIFT W TO NW WITHIN THE TROUGH 
OVER THE NEXT FEW DAYS...WITH WINDS TO 20 KT POSSIBLE ON BOTH 
SIDES OF THE TROUGH IN THE VICINITY OF THE LOWS. 

GLOBAL MODELS SHOW INCREASING WINDS AND BUILDING SEAS AROUND THE 
LOW SE OF THE GULF OF TEHUANTEPEC AS IT MOVES W TO W-NW OVER THE 
NEXT SEVERAL DAYS...AND WILL INCLUDE FRESH GAP WIND FLOW THROUGH 
THE GULF OF TEHUANTEPEC. SCATTERED MODERATE TO STRONG CONVECTION 
IS EXPECTED TO ACCOMPANY THIS BROAD CIRCULATION AS IT SHIFTS W 
DURING THE NEXT FEW DAYS.
  
$$
STRIPLING