000
AXPZ20 KNHC 172100
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC FRI APR 17 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 
1915 UTC.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG A LINE FROM 07N77W TO 09N87W TO 
05N105W TO 04N120W TO 05N140W. SCATTERED MODERATE CONVECTION CAN 
BE FOUND WITHIN 60 NM S OF THE ITCZ AXIS AND N OF THE ITCZ AXIS 
TO THE COAST OF PANAMA AND COSTA RICA BETWEEN 83W AND 85W. 
SCATTERED MODERATE CONVECTION ALSO LIES WITHIN 60 NM N AND 150 
NM S OF THE ITCZ AXIS BETWEEN 92W AND 96W.

...DISCUSSION...

N OF 20N...
THE TIGHT PRESSURE GRADIENT BETWEEN A 1031 MB HIGH CENTERED NEAR 
32N131W AND BROAD LOW PRES OVER THE EASTERN ROCKIES AND SOUTHERN 
PLAINS IS PRODUCING A SWATH OF NW WINDS TO 25 KT WITHIN 
APPROXIMATELY 300 NM W OF THE BAJA PENINSULA. THESE WINDS ARE 
EXPECTED TO DIMINISH TOMORROW AS HIGH PRES N OF AREA WEAKENS AND 
RETREATS FARTHER N. NW SWELL OFF BAJA CALIFORNIA IS ALREADY 
BEGINNING TO SUBSIDE AND WAVE HEIGHTS ARE EXPECTED TO FALL BELOW 
8 FT ON SAT. NW WINDS UP TO 25 KT WERE ALSO NOTED IN THE GULF OF 
CALIFORNIA ACCORDING TO THE 0106 UTC QUIKSCAT PASS...BUT SINCE 
THEN...NONE OF THE SCATTEROMETER PASSES HAVE HIT THE AREA OF 
HIGHEST WINDS AND THERE ARE NO SHIP OBSERVATIONS. THE 1158 UTC 
QUIKSCAT PASS DID CONFIRM THAT WINDS N OF 30N IN THE GULF OF 
CALIFORNIA HAVE DROPPED BELOW 20 KT...CONSISTENT WITH MODEL 
GUIDANCE. FOR NOW...THERE IS NO COMPELLING REASON TO ALTER THE 
FORECAST FOR WINDS TO 25 KT TO PERSIST OVER THE GULF FROM 23N TO 
28N UNTIL SUN MORNING. 

S OF 20N...
WHILE THE LA CUMBRE VOLCANO ON ISLA FERNANDINA IN THE GALAPAGOS 
ISLANDS LOCATED AT 00.4S91.5W CONTINUES TO ERUPT...THE 
GOVERNMENT OF ECUADOR REPORTS THAT THE RESULTING PLUME CONTAINS 
VAPOR AND GASES WITH NO SIGNIFICANT ASH. THE WASHINGTON VAAC HAS 
DISCONTINUED ASHFALL ADVISORIES. VISIBLE SATELLITE IMAGERY FROM 
1945 UTC SHOWS A CONCENTRATED PLUME EXTENDING WEST-NORTHWEST 
FROM THE VOLCANO APPROXIMATELY 100 NM. THIS PLUME LIKELY 
CONTAINS SULFUR DIOXIDE GAS. EXPOSURE TO THIS GAS CAN BE 
DANGEROUS...CAUSING IRRITATION TO EYES AND SKIN.

GAP WINDS...
NE WINDS IN THE 20 TO 25 KT CONTINUE TO FUNNEL THROUGH THE GULF 
OF PAPAGAYO. THIS FLOW SHOULD CONTINUE TO PULSE OVER THE NEXT 
FEW DAYS...ESPECIALLY IN THE EARLY MORNING HOURS WHEN DRAINAGE 
FLOW IS AT A MAXIMUM. THIS IS EVIDENT IN THE 1210 UTC QUIKSCAT 
PASS THIS MORNING WHICH REVEALED AN EXPANSION IN THE WIND FIELD 
COMPARED TO THE ASCAT PASS FROM YESTERDAY EVENING.

TRADE WINDS... 
THE QUIKSCAT PASSES FROM AROUND 1400 AND 1530 UTC SHOWED 
EASTERLY TRADES TO 25 KT ACROSS A LARGE PORTION OF THE FORECAST 
AREA N OF THE ITCZ W OF ABOUT 125W. THE IMPETUS SURFACE HIGH TO 
THE NORTH IS EXPECTED TO WEAKEN...MOVE FARTHER N...AND SHIFT THE 
RIDGE AXIS TO THE WEST OVER FORECAST WATERS OVER THE NEXT FEW 
DAYS. THIS SHOULD ALLOW THE TRADES TO DIMINISH IN SPEED AND AREA.

CONVECTION...
SCATTERED MODERATE CONVECTION CAN BE FOUND FROM THE COAST OF 
PANAMA AND COSTA RICA BETWEEN 83W AND 85W TO 60 NM S OF THE ITCZ 
AXIS. THIS CONVECTION ALREADY APPEARS TO BE WANING. THE BETTER 
LOW LEVEL CONVERGENCE IN THE REGION...AS EVIDENCED BY THE 1210 
UTC QUIKSCAT AND 1620 UTC ASCAT PASSES...LIES FARTHER W WITH THE 
AREA OF SCATTERED MODERATE CONVECTION WITHIN 60 NM N AND 150 NM 
S OF THE ITCZ AXIS BETWEEN 92W AND 96W. PRECIPITABLE WATER 
VALUES IN THE 2.0 TO 2.5 INCH RANGE COINCIDE WITH THIS MORE 
WESTERN AREA OF ACTIVE CONVECTION. CONVECTION IS LIKELY TO 
CONTINUE HERE INTO THE NIGHT.

$$
SCHAUER CLARK