000
AXPZ20 KNHC 210913
TWDEP 

TROPICAL WEATHER DISCUSSION                                   
NWS NATIONAL HURRICANE CENTER MIAMI FL                        
1005 UTC THU MAR 21 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 
0800 UTC.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...              
THE MONSOON TROUGH AXIS WAS ANALYZED FROM 08N83W TO 02N118W. 
ITCZ AXIS WAS ANALYZED FROM 02N118W TO 02N130W TO 01N140W. 
SCATTERED MODERATE CONVECTION WAS WITHIN 240 NM S OF THE AXIS 
BETWEEN 82W AND 92W. ISOLATED MODERATE CONVECTION WAS WITHIN 240 
NM N OF THE AXIS BETWEEN 103W AND 118W AS WELL AS WITHIN 90 NM S 
OF THE AXIS BETWEEN 109W AND 123W. SCATTERED MODERATE 
CONVECTION WAS WITHIN 180 NM N OF THE AXIS BETWEEN 125W AND 132W.

...DISCUSSION...                                                
AN UPPER LOW IS EVIDENT ON WATER VAPOR IMAGERY NEAR 15N110W. 
THIS LOW IS FORECAST TO OPEN INTO A TROUGH AND PASS E-NE THROUGH 
CENTRAL MEXICO TODAY INTO FRI. THERE IS NO SIGNIFICANT LOW-LEVEL 
REFLECTION OF THIS SYSTEM. INFRARED IMAGERY SHOWS THE UPPER JET 
ON THE E SIDE OF THE LOW IS TRANSPORTING MOISTURE FROM THE ITCZ 
NEAR 03N112W NORTHEASTWARD THROUGH ACAPULCO MEXICO AND INTO THE 
SW GULF OF MEXICO. HOWEVER....PRECIPITABLE WATER IMAGERY SHOWS 
LOW-LEVEL MOISTURE IS RELATIVELY LIMITED IN THE VICINITY OF THE 
JET N OF 10N. A BAND OF MAINLY CIRRUS EXTENDS ALONG THE JET 
AXIS...WITH SHOWER AND ISOLATED THUNDERSTORM ACTIVITY LIKELY 
LIMITED TO S OF 10N.

A POSITIVELY TILTED UPPER TROUGH LIES FROM 32N130W TO 20N140W. 
THE SOUTHWESTERLY UPPER JET ON THE E SIDE OF THE TROUGH HAS BEEN 
CUT OFF FROM THE TROPICAL MOISTURE...BUT STILL APPEARS TO 
SUPPORT MULTI-LAYERED CLOUDS E OF THE TROUGH AXIS N OF 25N. THIS 
TROUGH IS EXPECTED TO CUT OFF AN UPPER LOW OVER N CENTRAL WATERS 
ON FRI. ITS PRIMARY IMPACT ON THE SENSIBLE WEATHER WILL BE TO 
WEAKEN THE DEEP-LAYER RIDGING OVER NW WATERS WHICH WILL KEEP 
TRADE WINDS BELOW ADVISORY CONDITIONS THROUGH THE END OF THE 
FORECAST PERIOD EARLY SAT MORNING.

1031 MB HIGH PRESSURE IS WELL N OF THE AREA NEAR 40N138W. THE 
PRESSURE GRADIENT IS WEAK BETWEEN THE HIGH AND THE ITCZ OVER 
WESTERN WATERS. MODERATE TO FRESH TRADES ARE CONFINED BETWEEN 
THE ITCZ AND 16N. AN AREA OF MIXED NE AND SW SWELL WITH 8 FT 
SEAS...SEEN BY THE 0320 JASON-2 AND 0250 UTC JASON-1 PASSES... 
CONTINUES TO PROPAGATE WESTWARD NEAR THE REGION OF FRESH TRADE 
WINDS. THESE 8 FT SEAS COINCIDE WITH THE LEADING EDGE OF A NEW 
CROSS-EQUATORIAL SW SWELL TRAIN WITH PERIODS IN EXCESS OF 20 
SECONDS. SEAS HERE WILL SUBSIDE TODAY...AND THE LEADING EDGE OF 
THE SWELL WILL PROPAGATE NORTHEASTWARD REACHING THE COAST OF 
MUCH OF CENTRAL AMERICA AND MAINLAND MEXICO BY FRI AFTERNOON AND 
BAJA CALIFORNIA OVERNIGHT FRI NIGHT.

THE PRESSURE GRADIENT AT THE SURFACE WILL INCREASE TODAY OFF THE 
COAST OF SOUTHERN CALIFORNIA AND BAJA CALIFORNIA NORTE IN 
RESPONSE TO 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 GALE CONDITIONS N 
OF THE AREA. SEAS ARE EXPECTED TO BUILD TO 10 FT IN N-NW SWELL 
BY EARLY FRI MORNING AND TO 13 FEET BY EARLY SAT MORNING IN NE 
WATERS. A NEW SURGE OF LONG-PERIOD NW SWELL WILL MOVE INTO NW 
WATERS ON FRI...CARRYING SEAS AROUND 8 FT INTO THE AREA AND 
OVERLAPPING WITH THE AREA OF N-NW SWELL IN NE WATERS OVERNIGHT 
FRI NIGHT.

$$
SCHAUER