000
AXPZ20 KNHC 201601
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC MON APR 20 2009

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 INTERTROPICAL CONVERGENCE ZONE AXIS LIES ALONG 06N77W TO 
05N96W TO 08.5N114W TO 06N140W.  ISOLATED MODERATE CONVECTION 
WAS WITHIN 45 NM OF AXIS E OF 97W AND W OF 107W.

...DISCUSSION...
W OF 100W...REX BLOCK PATTERN CONTINUES THIS MORNING ...WITH CUT 
OFF UPPER CYCLONE NEAR 30N130W...AND LOCATED SOUTH OF AN UPPER 
RIDGE OFF THE OREGON COAST. LIFT ASSOCIATED WITH THE RIGHT REAR 
ENTRANCE REGION OF AN UPPER JET SOUTH OF THE UPPER CYCLONE HAS 
BEEN AIDING MODEST CONVECTION NEAR THE ITCZ BETWEEN 140W AND 
120W...AS WELL AS THE DEVELOPMENT OF A LOW AMPLITUDE SURFACE 
TROUGH ALONG THE ITCZ NEAR 125W. A SMALL AREA OF 20 KT ENE TRADE 
WINDS CONTINUES N AND NW OF THIS SURFACE TROUGH AND WEAK SURFACE 
HIGH PRES WELL NORTH OF THE AREA. THE REX BLOCK IS HINDERING THE 
EASTWARD ADVANCEMENT OF A SHARP LONG WAVE TROUGH ALONG 155W AND 
N OF THE HAWAII ISLANDS...AND A BROAD CUTOFF CYCLONE IS BECOMING 
EVIDENT NEAR 35N136W ON WATER VAPOR IMAGERY. THIS STAGNANT UPPER 
PATTERN WILL ALLOW A WEAK COLD FRONT TO SAG SOUTHWARD ALONG THE 
U.S. WEST COAST THROUGH MID WEEK...EFFECTIVELY CUTTING OFF A 
SURFACE HIGH PRES AREA NEAR 25N135W. THIS WILL KEEP WINDS FAIRLY 
MODEST N OF 15N THROUGH MID WEEK...BUT MAINTAIN 20 KT TRADES 
WINDS FURTHER S...MAINLY W OF 120W. MEANWHILE GFS AND ECMWF 
SHOWS THE UPPER CYCLONE NEAR 30N125W WILL OPEN UP GRADUALLY LIFT 
OVER THE BLOCKING RIDGE...AND THEN GRADUALLY BE ABSORBED IN THE 
DOWNSTREAM UPPER LOW TO THE EAST. THIS WILL ALLOW THE UPPER JET 
TO THE SOUTH TO WEAKEN...AND IN TURN...WILL ALLOW THE WEAK ITCZ 
CONVECTION TO DIMINISH AS WELL AT LEAST BY WED.

E OF 100W...THE MAIN ISSUE IS THE POTENTIAL FOR GALE FORCE WINDS 
THROUGH THE GULF OF TEHUANTEPEC. GFS MODEL GUIDANCE HAS 
FLUCTUATED IN STRENGTH FROM RUN TO RUN...BUT GLOBAL MODEL 
CONSENSUS INDICATES A MINIMAL GALE EVENT...WITH TWO POSSIBLE 
PULSES DURING THE NEXT 48 HOURS. WINDS HAS ALREADY BEGUN TO 
INCREASE THROUGH THE ISTHMUS OF TEHUANTEPEC THIS MORNING AS 
INDICATED BY A MORNING QUIKSCAT PASS...WITH MINIMAL GALES 
EXPECTED OVER THE GULF OF TEHUANTEPEC STARTING BY 
TONIGHT...FLUCTUATING NEAR GALE FORCE BY EARLY TUE AFTERNOON AND 
THEN INCREASING AGAIN WEDNESDAY MORNING. THE STRONG NORTHERLY 
WINDS WILL COINCIDE WITH THE ARRIVAL OF VERY LONG PERIOD SRN 
HEMI SSW SWELL...CREATING THE POTENTIAL FOR VERY ROUGH AND 
CONFUSED SEAS THROUGHOUT THE GULF OF TEHUANTEPEC. THE LONG 
PERIOD SWELL WILL IMPACT MUCH OF THE COASTLINE FROM PANAMA TO 
BAJA FROM TUE AFTERNOON THROUGH TUE NIGHT...WITH HIGH SURF 
LIKELY IN MOT EXPOSED AREAS. MEANWHILE PUFFS AND PULSES OF 20 KT 
WINDS WILL PERSIST THROUGH THE GULF OF PAPAGAYO...PRIMARILY IN 
THE MORNING HOURS...INCREASING BY MID WEEK TO 20 TO 25 KT AS 
REINFORCED TRADE WINDS FROM THE CARIBBEAN FUNNEL THROUGH THE 
AREA. FOR THE GULF OF PANAMA...A 11Z QUIKSCAT PASS SHOWED WINDS 
BACK UP TO AROUND 20 KT...BUT SHOULD FLUCTUATE AND FALL BELOW 20 
KT AGAIN BY 36 HOURS. THE CARIBBEAN TRADES WILL INCREASE BY 
MIDWEEK...BUT THEIR TRAJECTORY WILL BE MORE EASTERLY AND NOT 
EFFECTIVELY FUNNEL INTO THE GULF OF PANAMA.

$$
STRIPLING