000
AXPZ20 KNHC 221553
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC TUE OCT 21 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 
1515 UTC.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 08N80W TO 07N85W TO 12N90W TO 
10N120W TO 09N140W. SCATTERED MODERATE FROM 08N TO 12N BETWEEN 
91W AND 94W...FROM 10N TO 14N BETWEEN 100W AND 104W...FROM 
12N-14N BETWEEN 107W AND 111W...FROM 07N TO 10N BETWEEN 110W AND 
115W...AND FROM 07N TO 10N BETWEEN 136W TO BEYOND 140W.

...DISCUSSION...

A HIGHLY AMPLIFIED MID LEVEL PATTERN IS TAKING SHAPE N OF 
20N...WITH TROUGHING BUILDING OVER NW WATERS AND MUCH OF 
NORTHERN MEXICO WHILE RIDGING HOLDS STRONG IN BETWEEN ALONG 
125W.  A COLD FRONT ASSOCIATED WITH THE AMPLIFYING TROUGHING 
OVER MEXICO WILL SURGE SOUTHWARD THROUGH THE GULF OF MEXICO AND 
BRING STRONG NORTHERLY FLOW THROUGH CHIVELA PASS INTO THE GULF 
OF TEHUANTEPEC BY THU AFTERNOON/EVENING.  THE CURRENT FORECAST 
CALLS FOR THESE WINDS TO REMAIN BELOW GALE FORCE.  IN 
ADDITION...HIGH PRESSURE SPILLING SOUTHEASTWARD THROUGH THE 
SOUTHWESTERN CONUS BEHIND THIS COLD FRONT WILL INDUCE A STRONG 
PRESSURE GRADIENT OVER THE GULF OF CALIFORNIA.  NW WINDS ARE 
EXPECTED TO BUILD TO 30 KT IN THE GULF OF CALIFORNIA N OF 26N ON 
THU.

THE WEAK UPPER LOW OVER NW WATERS AT THE MOMENT IS BEING 
OVERTAKEN BY THE AMPLIFIED TROUGH APPROACHING THE FORECAST AREA 
FROM THE NORTHWEST.  THE COLD FRONT ASSOCIATED WITH THIS TROUGH 
WILL MOVE INTO NW WATERS TODAY...STALL...AND WEAKEN WHILE THE 
MID LEVEL TROUGH PINCHES OFF A CUT OFF LOW ALONG 140W THAT WILL 
GRAZE THE AREA.  THE SURFACE REFLECTION OF THIS ACTIVITY 
ALOFT...A TROUGH ON THE SOUTHEASTERN EDGE OF THE SUBTROPICAL 
RIDGE...WILL LINGER FOR THE NEXT FEW DAYS DISRUPTING THE 
NORTHEASTERLY FLOW.  NW SWELL INDUCED BY THE COLD FRONT WILL 
PUSH INTO THE FORECAST AREA THU...ELEVATING SEAS TO THE 8 TO 11 
FT RANGE.  MEANWHILE...THE 20 TO 25 KT EASTERLY TRADE WINDS 
FOUND BETWEEN 10N AND 20N W OF 125W WILL WEAKEN TO 20 KT DUE TO 
THE DISRUPTION IN THE DEEP LAYER ANTICYCLONIC FLOW.

A 1010 MB LOW PRESSURE SYSTEM CURRENTLY NEAR 11N104W IS EXPECTED 
TO CONTINUE ON A WNW PATH OVER THE NEXT FEW DAYS TOWARD THE 
AMPLIFYING MID TO UPPER LEVEL TROUGHING JUST S OF BAJA 
CALIFORNIA.  THE SYSTEM WILL ENCOUNTER STRONG SW UPPER LEVEL 
FLOW ON THE LEADING EDGE OF THE AMPLIFYING TROUGH BY THU.  THIS 
WILL LIMIT THE DEVELOPMENT OF DEEP CONVECTION NEAR THE LOW. 
WHATEVER IS LEFT OF THE SYSTEM AS IT MOVES INTO AN ENVIRONMENT 
OF STRONG VERTICAL WIND SHEAR WILL BE PULLED NORTH TO 
NORTHEASTWARD INTO THE LEADING EDGE OF THE TROUGH FRI.

A TROPICAL WAVE IS ENTERING THE AREA ALONG 78W N OF 78W MOVING W 
AT 10 KT. ISOLATED MODERATE CONVECTION IS WITHIN 60 NM OF THE 
WAVE AXIS. 

$$
FORMOSA