000
AXPZ20 KNHC 281555
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC MON APR 28 2008

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1500 UTC.

...ITCZ...
ITCZ AXIS RUNS FROM 06N77W TO 5N89W TO 4N95W TO 6N115W TO 2N137W 
TO 2N140W. SCATTERED MODERATE CONVECTION WITHIN 90 NM N OF AXIS 
E OF 80W. SCATTERED MODERATE ISOLATED STRONG CONVECTION WITHIN 
90 NM OF AXIS BETWEEN 89W AND 108W. 

SCATTERED MODERATE CONVECTION N OF ITCZ FROM 08N TO 10N BETWEEN 
112W AND 116W.

...DISCUSSION...

E OF 115W...
A LATE SEASON COLD FRONT IS BRINGING GALE CONDITIONS TO THE SW 
GULF OF MEXICO THIS MORNING. THE COOL HIGH PRESSURE AIRMASS 
BUILDING BEHIND THE FRONT WILL FUNNEL THROUGH THE TEHUANTEPEC 
ISTHMUS LATER THIS EVENING...AND BRING GALE CONDITIONS TO THE 
GULF OF TEHUANTEPEC. THE UPPER SUPPORT FOR THE COLD FRONT IS A 
LONG WAVE TROUGH EXTENDING FROM THE GREAT LAKES THROUGH NORTHERN 
MEXICO TO 20N115W. THE TROUGH REMAINS FAIRLY PROGRESSIVE 
HOWEVER. THE SURFACE HIGH PRES BEHIND THE FRONT WILL SHIFT 
EASTWARD AS A RESULT...ALLOWING RAPID RETURN FLOW OVER THE GULF 
OF MEXICO AND DIMINISHING WINDS IN THE GULF OF TEHUANTEPEC ON 
TUE...WITH THE GALE ENDING BY MIDDAY. MEANWHILE MOIST SOUTHWEST 
FLOW ALOFT AHEAD OF THE TROUGH IS PROVIDING THE EXHAUST TO 
SUPPORT CLUSTERS OF CONVECTION ALONG THE ITCZ. THIS MAY WEAKEN 
THROUGH MID WEEK AS THE UPPER TROUGH DAMPENS OUT AND SHIFTS 
EAST...ALLOWING UPPER WINDS TO BECOME MORE ZONAL. FURTHER 
NORTH...VERY DRY SUBSIDENT AIR IS NOTED BEHIND THE TROUGH OVER 
NW MEXICO AND ADJACENT PACIFIC WATERS. MEANWHILE A PAIR OF SW 
SWELL GROUPS WITH PERIODS OF 15 TO 17 SECONDS WILL PUSH INTO THE 
AREA THROUGH MID WEEK.

W OF 115W...
UPPER PATTERN REMAINS FAIRLY AMPLIFIED N OF 20N WITH A MID/UPPER 
RIDGE ALONG 120W...AHEAD OF A LARGE AMPLITUDE UPPER TROUGH 
EXTENDING FROM THE FAR NORTH PACIFIC TO JUST N OF HAWAII. THE 
RIDGE WILL FLATTEN OUT AS THE LARGE UPPER TROUGH RIDES TO THE 
NORTH. A 1030 MB SURFACE HIGH CENTERED NEAR 26N152W WILL SHIFT 
EWD BEHIND THE TROUGH. FRESH TO STRONG NORTH FLOW ALREADY 
EVIDENT OFF THE CALIFORNIA COAST ON THE EAST EDGE OF THIS 
SURFACE HIGH WILL SURGE SOUTHWARD OFF THE NORTHERN BAJA COAST 
THROUGH MID WEEK AS THE SURFACE HIGH SHIFTS EASTWARD. TRADES TO 
THE SOUTH OF THE HIGH WILL SLIGHTLY INCREASE AS WELL. FURTHER 
SOUTH...AND UPPER TROUGH EXTENDS FROM HAWAII TO EQ120W...WITH A 
PARALLEL UPPER RIDGE AXIS TO ITS NE FROM 10N115W TO 20N145W. 
SOUTHERLY DIFFLUENT FLOW ALOFT DOES NOT SEEM TO BE INFLUENCING 
THE RELATIVELY MODEST CONVECTION ALONG THE ITCZ W OF 
115W...PERHAPS DUE TO LIMITED LOW LEVEL CONVERGENCE DUE TO LIGHT 
CROSS EQUATORIAL SURFACE WINDS. SOME INCREASE IN CONVECTION IS 
POSSIBLE ALONG THE ITCZ AS THE UPPER PATTERN CONTINUES THROUGH 
MID WEEK. MEANWHILE...LONG PERIOD SW SWELL WILL CONVERGE WITH NW 
SWELL AND MODERATE TO FRESH NORTHERLY AND EASTERLY WIND WAVES TO 
CREATE POSSIBLE CONFUSED SEA CONDITIONS...MAINLY N OF 20N TUE 
AND WED.

$$
CHRISTENSEN