000
AXPZ20 KNHC 200947
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC MON APR 20 2009

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 
0900 UTC.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE AXIS LIES ALONG 04N77W TO 
06N90W TO 05N110W TO 06N130W TO 05N140W. NO SIGNIFICANT 
CONVECTION ALONG THE ITCZ.

...DISCUSSION...
W OF 100W...REX BLOCK PATTERN CONTINUES THIS MORNING WITH CUT 
OFF UPPER CYCLONE NEAR 30N130W SOUTH OF AN UPPER RIDGE OFF THE 
OREGON COAST. LIFT ASSOCIATED WITH THE RIGHT REAR ENTRANCE AREA 
OF AN UPPER JET SOUTH OF THE UPPER CYCLONE HAS BEEN AIDING 
MODEST CONVECTION NEAR THE ITCZ NEAR 120W AS WELL DEVELOPMENT OF 
A LOW AMPLITUDE SURFACE TROUGH ALONG THE ITCZ NEAR 130W. 
SCATTEROMETER DATA FROM YESTERDAY JIVED WITH MODEL 
INITIALIZATIONS SHOWING A SMALL AREA OF 20 KT TRADE WINDS 
BETWEEN THE SURFACE TROUGH AND WEAK SURFACE HIGH PRES WELL NORTH 
OF THE AREA. THE REX BLOCK IS FRUSTRATING THE EASTWARD 
ADVANCEMENT OF A SHARP LONG WAVE TROUGH ALONG 155W N OF 
HAWAII...AND A BROAD CUTOFF CYCLONE IS BECOMING EVIDENT NEAR 
35N135W ON WATER VAPOR IMAGERY. THIS 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 LIGHT 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 
30N105W WILL OPEN UP AND BE ABSORBED IN THE LOW TO THE 
EAST...ALLOWING THE UPPER JET TO THE SOUTH TO DIMINISH. THIS IN 
TURN WILL ALLOW THE WEAK ITCZ CONVECTION TO DIMINISH AS WELL AT 
LEAST BY WED.

E OF 100W...MAIN ISSUE IS THE POTENTIAL FOR GALE FORCE WINDS 
THROUGH THE GULF OF TEHUANTEPEC...ALTHOUGH CURRENT THINKING IS 
THAT THIS EVENT WILL BARELY REACH GALE FORCE AND BE SHORT LIVED. 
SURFACE PRESSURE VALUES OVER TEXAS AND NE MEXICO ARE ONLY AROUND 
1022 MB AS THE HIGH PRES SHIFTS INTO THE NW GULF OF MEXICO 
BEHIND A COLD FRONT. IN ADDITION...COLD AIR ADVECTION IS 
NATURALLY NOT THAT GREAT THIS LATE IN THE SEASON. WINDS WILL 
INCREASE THROUGH THE ISTHMUS OF TEHUANTEPEC THROUGH TODAY...WITH 
MINIMAL GALE POSSIBLE OVER THE GULF OF TEHUANTEPEC STARTING BY 
TONIGHT...BUT DIMINISHING BELOW GALE FORCE BY EARLY TUE 
AFTERNOON. THE STRONG NORTHERLY WINDS WILL COINCIDE WITH THE 
ARRIVAL OF 20 SECOND SW 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 SOME AREAS. MEANWHILE PUFFS 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 00Z QUIKSCAT PASS AND SHIP OBSERVATIONS DID 
NOT SHOW EVIDENCE OF 20 KT FLOW...INDICATING THAT THE CURRENTLY 
WEAKENING CARIBBEAN TRADES HAVE STOPPED FUNNELING THROUGH THE 
ISTHMUS. ALTHOUGH THE CARIBBEAN TRADES WILL INCREASE BY 
MIDWEEK...THEIR TRAJECTORY WILL BE MORE EASTERLY AND NOT 
EFFECTIVELY FUNNEL INTO THE GULF OF PANAMA.

$$
CHRISTENSEN