000
AXPZ20 KNHC 210954
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC TUE OCT 21 2008

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

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0800 UTC.

...ITCZ...

THE ITCZ AXIS LIES ALONG A LINE FROM 09N79W TO 07N83W TO 10N96W 
TO 09N106W TO 08N140W. SCATTERED MODERATE CONVECTION CAN BE 
FOUND WITHIN 90 NM N AND 45 NM S OF AXIS W OF 138W AND WITHIN 
180 NM OF AXIS FROM 117W AND 122W. SCATTERED MODERATE WITH 
ISOLATED STRONG CONVECTION CAN BE FOUND WITHIN 60 NM OF AXIS 
FROM 100W TO 104W.

...DISCUSSION...

THE UPPER LEVEL PATTERN SPORTS TWO ANTICYCLONES ALONG 
135W...ONE NEAR 13N AND ANOTHER NEAR 33N...SEPARATED BY A TROUGH 
STRETCHED OVER NORTH WATERS WHOSE LEADING EDGE IS PASSING 
EASTWARD INTO NW MEXICO AT THE MOMENT.  THE ANTICYCLONE TO THE N 
IS EXPECTED TO MOVE EASTWARD AS WELL AND WILL HELP PINCH OFF A 
LOW FROM THIS TROUGH WHICH WILL RETROGRADE OVER NW WATERS AND 
EVENTUALLY BE PICKED UP BY THE NEXT APPROACHING PACIFIC LONGWAVE 
TROUGH ON WED.  AT THE SURFACE...A WEAKENING COLD FRONT 
ASSOCIATED WITH THE LONGWAVE TROUGH WILL GRAZE NW WATERS WED AND 
DISSIPATE THU...BUT NOT BEFORE ELEVATING SEAS TO THE 9 TO 12 FT 
RANGE IN NW SWELL.  IN ADDITION...THE DOMINANT HIGH PRESSURE AT 
THE SURFACE WILL SLACKEN UNDER THE UPPER LOW OVER NW 
WATERS...WEAKENING THE EASTERLY TRADES BETWEEN 10N AND 20N TO 20 
KT OR LESS BY WED.

MEANWHILE...THE TROUGH CURRENTLY MOVING INTO MEXICO WILL PHASE 
WITH NORTHERN STREAM ENERGY OVER THE ROCKIES LATER TODAY WITH A 
CUT OFF LOW EXPECTED TO DEVELOP OVER THE PLAINS WED.  THIS WILL 
SEND A STRONG COLD FRONT SOUTHWARD THROUGH EASTERN MEXICO AND 
THE WESTERN GULF OF MEXICO BY THU AND BRING A RETURN OF STRONG 
WINDS THROUGH THE CHIVELA PASS AND INTO THE GULF OF TEHUANTEPEC 
LATE IN THE WEEK.  

CURRENTLY...WINDS HAVE DIMINISHED BELOW GALE FORCE IN THE GULF 
OF TEHUANTEPEC ACCORDING TO A 0328 UTC ASCAT PASS.  THE PRESSURE 
GRADIENT OVER THE REGION IS EXPECTED TO GRADUALLY SLACKEN OVER 
THE NEXT TWO DAYS...PRIOR TO THE ARRIVAL OF THE COLD FRONT IN 
THE GULF OF MEXICO...AS HIGH PRESSURE OVER MEXICO WEAKENS AND 
THE BROAD AREA OF LOW PRESSURE OVER CENTRAL AMERICA IS 
SPLIT...WITH THE MID LEVEL TROUGHING AND ASSOCIATED SURFACE LOW 
NEAR 11N99W PASS EASTWARD AWAY FROM THE TROUGHING OVER THE GULF 
OF HONDURAS AND TOWARD THE MID TO UPPER LEVEL TROUGH PASSING 
SOUTHWARD THROUGH NW MEXICO.  THIS LOW PRESSURE SYSTEM...NEAR 
11N99W AT 0600 UTC...SUPPORTS NUMEROUS MODERATE WITH ISOLATED 
STRONG CONVECTION WITHIN 180 NM E QUADRANT OF ITS CENTER.  

$$
SCHAUER CLARK