000
AXPZ20 KNHC 200915
TWDEP 

TROPICAL WEATHER DISCUSSION                                   
NWS NATIONAL HURRICANE CENTER MIAMI FL                        
1005 UTC WED MAR 20 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 
0730 UTC.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...             
THE MONSOON TROUGH AXIS WAS ANALYZED FROM 10N85W TO 08N90W. THE 
ITCZ AXIS WAS ANALYZED FROM 08N90W TO 00N102W THEN CONTINUES 
FROM 03N106W TO 04N125W TO 02N140W. SCATTERED MODERATE TO STRONG 
CONVECTION WAS FROM 90 NM TO 270 NM S OF THE AXIS BETWEEN 88W 
AND 91W. SCATTERED MODERATE CONVECTION WAS WITHIN 60 NM N AND 
180 NM S OF THE AXIS BETWEEN 113W AND 127W AS WELL AS WITHIN 90 
NM N AND 45 NM S OF THE AXIS W OF 135W.

...DISCUSSION...                                                
A POSITIVELY TILTED UPPER-LEVEL TROUGH EXTENDS ACROSS MEXICO AND 
THE EASTERN PACIFIC FROM BROWNSVILLE TEXAS TO 20N110W TO 
05N120W. THE TROUGH IS FORECAST TO CUT OFF AN UPPER LOW NEAR 
16N110W BY THIS EVENING BEFORE WEAKENING AND MOVING E-NE INTO 
CENTRAL MEXICO. THERE IS NO SIGNIFICANT LOW-LEVEL REFLECTION OF 
THIS SYSTEM. PRECIPITABLE WATER IMAGERY SHOWS MOISTURE IS 
RELATIVELY LIMITED ON THE SE SIDE OF THE TROUGH...LIMITING THE 
CHANCE OF ANY SIGNIFICANT CONVECTION. 

A MEAN UPPER TROUGH LIES ALONG 140W N OF 05N. THE SOUTHWESTERLY 
UPPER JET ON THE E SIDE OF THE TROUGH IS TRANSPORTING MOISTURE 
INTO THE FORECAST AREA PRIMARILY W OF A LINE FROM 10N140W TO 
10N130W TO 32N117W...WITH SHOWER ACTIVITY BELIEVED TO BE FOUND 
MAINLY OVER NW WATERS AHEAD OF A WEAKENING COLD FRONT. THAT COLD 
FRONT LIES OVER THE FORECAST AREA FROM 32N132W TO 27N140W. THE 
COLD FRONT IS EXPECTED TO DISSIPATE S OF 32N TODAY. 
PRECIPITATION WILL BE ITS MAIN CONTRIBUTION OF THE SENSIBLE 
WEATHER OVER THE FORECAST AREA...WITH WINDS AND SEAS 
REMAINING BELOW ADVISORY CONDITIONS.

THE 1023 MB SUBTROPICAL HIGH HAS BEEN FORCED SOUTHWARD TO 
29N126W. THE PRESSURE GRADIENT IS WEAK BETWEEN THE HIGH AND THE 
ITCZ OVER WESTERN WATERS. MODERATE TO FRESH TRADES ARE CONFINED 
BETWEEN THE ITCZ AND 20N. AN AREA OF MIXED NE AND SW SWELL WITH 
SEAS TO 8 FT CONTINUES TO PROPAGATE WESTWARD INTO THE AREA OF 
FRESH TRADE WINDS CAUGHT BETWEEN THE 0436 UTC AND 0616 UTC ASCAT 
PASSES. THE JASON-1 PASS FROM 0240 UTC SAW 8 FT SEAS CENTERED 
ALONG 116W FROM 03N-10N. THE AREA OF FRESH WINDS WILL DIMINISH 
TODAY AS THE SUBTROPICAL HIGH REORGANIZES WELL TO THE NW OF ITS 
CURRENT POSITION. HOWEVER...THE LEADING EDGE OF A NEW CROSS-
EQUATORIAL SW SWELL TRAIN WITH PERIODS IN EXCESS OF 20 SECONDS 
WILL MOVE THROUGH THIS AREA OVERNIGHT TONIGHT AND HELP KEEP SEAS 
TO 8 FT.

THE PRESSURE GRADIENT AT THE SURFACE WILL INCREASE OVERNIGHT THU 
NIGHT OFF THE COAST OF SOUTHERN CALIFORNIA AND BAJA CALIFORNIA 
NORTE IN RESPONSE TO THE REORGANIZING SUBTROPICAL HIGH AND 
INCREASED TROUGHING OVER THE INTERMOUNTAIN WESTERN U.S. THIS 
WILL BRING A FRESH TO STRONG N-NW BREEZE TO NE FORECAST WATERS 
OFF BAJA CALIFORNIA NORTE...WITH SEAS BUILDING TO 9 FT BY EARLY 
FRI MORNING. 

$$
SCHAUER