000
AXPZ20 KNHC 182112
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC SAT APR 18 2009

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

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2000 UTC.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE LIES ALONG A LINE FROM 04N77W 
TO 04N80W TO 08N110W TO 07N125W TO 05N140W. ISOLATED MODERATE 
CONVECTION CAN BE FOUND WITHIN 90 NM OF THE ITCZ AXIS FROM 85W 
TO 89W AND WITHIN 45 NM N AND 210 NM S OF THE ITCZ AXIS FROM 
120W TO 126W. SCATTERED MODERATE CONVECTION LIES WITHIN 120 NM N 
AND 90 NM S OF THE ITCZ AXIS W OF 132W.

...DISCUSSION...

1029 MB HIGH PRES N OF THE AREA NEAR 40N130W WILL CONTINUE TO 
WEAKEN AND SHIFT NORTHWARD OVER THE NEXT FEW DAYS. THIS IS THE 
RESULT OF THE MIGRATION OF THE ASSOCIATED MID LEVEL HIGH CENTER 
WHICH WILL BE NUDGED NORTHWARD BY THE MID LEVEL LOW TO ITS 
SOUTH...CURRENTLY OVER NW WATERS...AS IT IS FORCED NORTHWARD ON 
THE LEADING EDGE OF THE DEEP LAYER TROUGH AMPLIFYING TO ITS W IN 
THE VICINITY OF HAWAII. WITH THE SURFACE RIDGE WEAKENED...TRADE 
WINDS ARE EXPECTED TO DIMINISH IN TURN. IN THE MEAN TIME...THE 
PRESSURE GRADIENT BETWEEN THE SURFACE HIGH N OF THE AREA AND 
BROAD LOW PRESSURE OVER THE CENTRAL U.S. AND EASTERN MEXICO 
CONTINUES TO BRING WINDY CONDITIONS IN THE GULF OF CALIFORNIA 
...WITH THE 1330 UTC QUIKSCAT PASS SHOWING NW FLOW TO 25 KT IN 
MUCH OF THE WESTERN GULF OF CALIFORNIA S OF 28N AND THE ASCAT 
PASS FROM 1736 UTC CONFIRMING THESE WINDS ARE STILL IN PLACE 
OVER THE SOUTHERN HALF OF THE GULF. WINDS ARE EXPECTED TO 
DIMINISH HERE ON SUN.

GAP WINDS...
GULF OF PAPAGAYO...NE WINDS TO 25 KT ARE FUNNELING THROUGH 
THE GULF OF PAPAGAYO ACCORDING TO SHIP 9HJD6 AND THE 1558 UTC 
ASCAT PASS. THIS FLOW WILL CONTINUE TO PULSE OVER THE NEXT 
DAY OR TWO...ESPECIALLY IN THE EARLY MORNING HOURS WHEN DRAINAGE 
FLOW IS AT A MAXIMUM. HOWEVER...LOOK FOR WIND SPEEDS TO COME 
DOWN STARTING SUN NIGHT AS THE HIGH PRES SYSTEM CURRENTLY ALONG 
THE SE U.S. COAST SHIFTS EASTWARD.

GULF OF PANAMA...ACCORDING TO OBSERVATIONS FROM SHIP ZCDF4 AND 
THE 1144 UTC QUIKSCAT PASS...NORTHERLY FLOW TO 20 KT IS REPORTED 
FROM THE GULF OF PANAMA S TO 06N AS A RESULT OF THE FUNNELING 
NORTH-NORTHEAST TRADE WIND FLOW IN THE SW CARIBBEAN THROUGH 
PANAMA. LIKE PAPAGAYO...EXPECT WINDS TO DIMINISH AND SHIFT MORE 
EASTERLY AS THE IMPETUS HIGH PRESSURE IN THE ATLC IS FORCED 
EASTWARD OVER THE NEXT FEW DAYS.

GULF OF TEHUANTEPEC...MODEL GUIDANCE SUGGESTS WINDS IN THE GULF 
OF TEHUANTEPEC MAY REACH GALE FORCE TUE AS THE DEEP LAYER TROUGH 
OVER THE CENTRAL U.S. RECEIVES A REINFORCING SHOT OF NORTHERN 
STREAM ENERGY AND SENDS STRONG NORTHERLY FLOW AT THE SURFACE 
THROUGH THE ISTHMUS OF TEHUANTEPEC.

CONVECTION...
ISOLATED MODERATE CONVECTION WITHIN 90 NM OF THE ITCZ AXIS FROM 
85W TO 89W...75 NM OR MORE OFF THE COAST OF COSTA RICA...IS 
ASSISTED BY THE LOW LEVEL CONVERGENCE EVIDENT IN THE 1144 UTC 
QUIKSCAT PASS AND 2.0 TO 2.25 INCH PRECIPITABLE WATER VALUES IN 
THE REGION. THE BROAD UPPER LEVEL DIFFLUENCE CURRENTLY IN PLACE 
HERE SHOULD BE DIMINISHING OVER THE NEXT FEW HOURS.

FARTHER W...CONVECTION NOTED IN THE VICINITY OF THE ITCZ W OF 
120W ACCOMPANIES A SWATH OF 2.0 TO 2.5 INCH PRECIPITABLE WATER 
VALUES AND MODERATE LOW LEVEL CONVERGENCE AS NOTED IN THE 1504 
UTC QUIKSCAT PASS...BUT DOES NOT HAVE A ROBUST SOURCE OF UPPER 
LEVEL DIFFLUENCE ASSOCIATED WITH IT TO HELP LIFT THE MOISTURE 
AND CREATE DEEP CONVECTION. MODEL GUIDANCE SHOWS THIS CONVECTION 
WANING OVER THE NEXT FEW HOURS.

$$
SCHAUER CLARK