000
AXPZ20 KNHC 211558
TWDEP 

TROPICAL WEATHER DISCUSSION  
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC WED MAR 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...

NEITHER ITCZ AND MONSOON TROUGH IS IDENTIFIABLE AT THIS TIME. NO 
SIGNIFICANT CONVECTION IS NOTED.

...DISCUSSION...

AN UPPER LEVEL ANTICYCLONE NEAR 26N122W WITH ASSOCIATED 
BROAD RIDGING THAT HAS DOMINATED THE MAJORITY OF THE DISCUSSION
AREA DURING THE PAST FEW DAYS IS NOW SHIFTING EASTWARD IN 
RESPONSE TO A LONG WAVE TROUGH APPROACHING THE FAR NW PORTION
OF THE AREA. AN UPPER TROUGH AHEAD OF THE LONGWAVE HAS ENTERED 
THE NW PART OF THE AREA ALONG 134W N OF 22N. E OF THE DISCUSSION
REGION...A SLOW MOVING DEEP LAYERED CYCLONE ACROSS THE CENTRAL 
U.S. IS CENTERED OVER N CENTRAL TEXAS WITH AN ASSOCIATED 
MID/UPPER LEVEL TROUGH EXTENDING SW ACROSS CENTRAL MEXICO AND TO 
NEAR 19N119W. UPPER LEVEL WESTERLIES PREVAIL TO THE S OF THESE 
FEATURES...MAINLY S OF 13N FLOWING E ACROSS CENTRAL AMERICA.   

THE BROAD RIDGE HAS SUPPORTED A VERY BROAD SURFACE RIDGE THE 
PAST FEW DAYS THEN HAS ALSO BEGUN TO WEAKEN...NOW ANCHORED ON A 
1025 MB HIGH NEAR 29N133W...EXTENDING SE TO NEAR 19N112W. THE 
PRES GRADIENT BETWEEN THE HIGH AND ELONGATED LOW PRES ACROSS 
MEXICO IS INDUCING NW 20 KT WINDS WITHIN ABOUT 150 NM OF THE
COAST OF THE BAJA CALIFORNIA PENINSULA. THESE WINDS HAVE 
DIMINISHED FROM THE EARLIER 20-25 KT RANGE...AND ARE FORECAST
TO DIMINISH TO LESS THAN 20 KT BY 24 HRS. THROUGH THE GULF
OF CALIFORNIA...NW WINDS OF 20-25 KT ARE CONFINED TO MAINLY
FROM 23N TO 29N. THESE WINDS ARE FORECAST TO SHRINK IN AREAL
COVERAGE BY 24 HRS...AND DROP TO LESS THAN 20 KT BY 48 HRS
OR EARLIER.

S OF THE RIDGE...AN ELONGATED ZONE OF FRESH NELY TRADEWINDS 
PREVAILS FROM 06N TO 16N W OF 122W AND ALSO FROM 09N TO 15N 
BETWEEN 111W AND 122W. NE WIND WAVES ARE COMBINING WITH MODERATE 
TO LARGE NW SWELL ACROSS THE REGION TO PRODUCE SEAS OF 8 TO 10 
FT. ALTHOUGH NO TRUE ITCZ CURRENTLY EXISTS ACROSS THE AREA...AN 
ELONGATED CONVERGENCE ZONE ALONG THE S PERIPHERY OF THE TRADE
WINDS IS RESULTING IN A 180-210 NM WIDE SWATH OF MOSTLY BROKEN
LOW AND MIDDLE LEVEL CLOUDS WITH POSSIBLE WIDELY SCATTERED TO 
SCATTERED SHOWERS. ISOLATED WEAK CONVECTION IS NOTED WITHIN 150 
NM S OF THE TRADES BETWEEN 111W-116W.

A COLD FRONT SUPPORTED BY THE APPROACHING LONG WAVE TROUGH WILL 
MOVE INTO THE FAR NW PORTION OF THE FORECAST AREA EARLY THIS 
EVENING ROUGHLY ALONG A LINE FROM 32N132W TO 28N140W. THE FRONT 
WILL SERVE AS AN AID IN THE SURFACE HIGH SHIFTING SE AND 
WEAKENING THROUGH THE NEXT 24-48 HRS. THIS WILL ACT TO 
SIGNIFICANTLY WEAKEN THE PRESSURE GRADIENT TO BOTH THE E AND S 
OF THE RIDGE LEADING TO WEAKENING WINDS ACROSS MUCH OF THE AREA. 
THE COLD FRONT IS FORECAST TO REACH FROM 30N130W TO 27N135W
TO 28N140W BY 24 HRS...THEN BEGIN TO DISSIPATE AS IT REACHES
FROM 30N123W TO 24N104W BY 48 HRS. A TIGHT PRES GRADIENT NW 
OF THE FRONT WILL BRING N WINDS OF 20-25 KT BEHIND IT...BUT
WINDS GRADUALLY VEER AROUND TO THE NE AND DIMINISH TO 20 KT
BY 48 HRS WITHIN 150 NM NW OF THE COLD FRONT.

TO THE E AND SE OF THE RIDGE...TWO LOW LEVEL TROUGHS EXIST AND 
ARE FORCING CONVECTION. THE FIRST TROUGH EXTENDS FROM JUST SE
OF THE GULF OF TEHUANTEPEC SW TO NEAR 08N111W. WIDELY SCATTERED
TO ISOLATED WEAK CONVECTION EMBEDDED WITHIN BROKEN TO OVERCAST
LOW AND MID LEVEL CLOUDS IS WITHIN 60 NM SE OF THIS TROUGH. A
MORE PERSISTENT TROUGH OVER THE PAST SEVERAL DAYS...COULD SAY IT 
HAS JUST BECOME A CLIMATOLOGICAL TYPE FEATURE...EXTENDS FROM 
CENTRAL COSTA RICA SW TO 05N91W TO NEAR 02N99W. SCATTERED 
MODERATE/ISOLATED STRONG CONVECTION IS OBSERVED WITHIN 180 NM SE 
OF THE TROUGH. THIS AREA OF CONVECTION IS EXPECTED TO REMAIN 
VERY ACTIVE THROUGH THIS AFTERNOON BEFORE WEAKENING AND SHIFTING 
SW TONIGHT INTO THU. OTHERWISE...LIGHT TO MODERATE WINDS UNDER A 
WEAK PRES PATTERN WITH LOW SEA STATE OF 6 OF LESS PREVAIL 
GENERALLY TO THE E OF 105W.

ALSO WITH REGARDS TO MARINE ISSUES...VERY LONG PERIOD SRN 
HEMISPHERIC SWELLS ARE FORECAST TO MOVE INTO THIS AREA THU 
EVENING AND ACT TO ELEVATE SEA HEIGHTS TO POSSIBLY AROUND
8 FT ALONG THE EQUATOR...WITH A GOOD CHANCE THAT THE 
ASSOCIATED WAVE ENERGY WILL LEAD TO LARGE AND POWERFUL SURF
CONDITIONS TO THE CENTRAL AMERICAN COAST THU NIGHT THROUGH FRI. 

$$
AGUIRRE