000
AXPZ20 KNHC 180334
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC FRI APR 17 2009

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

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0130 UTC.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG A LINE FROM 05N77W TO 09N88W TO 
06N103W TO 04N120W TO 04N140W. THERE ARE NO AREAS OF SIGNIFICANT 
CONVECTION ASSOCIATED WITH THE ITCZ AT THIS TIME.

...DISCUSSION...

N OF 20N...
THE PRESSURE GRADIENT BETWEEN A 1031 MB HIGH CENTERED NEAR 
33N131W AND BROAD LOW PRES OVER THE EASTERN ROCKIES AND SOUTHERN 
PLAINS HAS BEGUN TO SLACKEN. THE ASCAT PASS FROM 1756 UTC ONLY 
SHOWS WINDS TO 20 KT OFF THE BAJA. HOWEVER...SHIP A8ER9 NEAR 
29N122W AT 0000 UTC REPORTED WINDS TO 23 KT. ASCAT GENERALLY 
RUNS LOW...SO BELIEVE THE WINDS REMAIN IN THE 20 TO 25 KT RANGE 
OVER N CENTRAL TO NE WATERS AT THIS TIME. THESE WINDS ARE 
EXPECTED TO DIMINISH BELOW 20 KT SAT 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 SAT. NW WINDS UP TO 25 KT WERE ALSO NOTED IN THE 
GULF OF CALIFORNIA ACCORDING TO THE 17/0106 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 1756 UTC ASCAT PASS DID CONFIRM THAT WINDS 
N OF 30N IN THE GULF OF CALIFORNIA HAVE DROPPED BELOW 20 
KT...CONSISTENT WITH MODEL GUIDANCE. FOR NOW...THE FORECAST 
FOLLOWS MODEL GUIDANCE...KEEPING WINDS ABOVE 20 KT IN THE 
CENTRAL GULF OF CALIFORNIA UNTIL SUN MORNING. 

S OF 20N...
THE ERUPTION OF THE LA CUMBRE VOLCANO ON ISLA FERNANDINA IN THE 
GALAPAGOS ISLANDS LOCATED AT 00.4S91.5W APPEARS TO HAVE TAPERED 
OFF SIGNIFICANTLY OVER THE LAST 24 HOURS. THE LAST VISIBLE 
IMAGERY OF THE DAY SHOWED A CONCENTRATED PLUME EXTENDING 
WEST-NORTHWEST FROM LA CUMBRE APPROXIMATELY 75 NM. THIS PLUME 
MAY CONTAIN SULFUR DIOXIDE GAS WHICH CAN CAUSE IRRITATION TO 
EYES AND SKIN. HOWEVER...NO SIGNIFICANT ASH IS REPORTED BY THE 
WASHINGTON VAAC ASSOCIATED WITH THE ERUPTION.

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.  LOOKING 
AHEAD...MODEL GUIDANCE SUGGESTS WINDS IN THE GULF OF TEHUANTEPEC 
MAY REACH GALE FORCE TUE AS THE DEEP LAYER TROUGH OVER THE 
ROCKIES SLOWLY MOVES ITS WAY INTO THE WESTERN GULF OF 
MEXICO...BRINING STRONG NORTHERLY FLOW AT THE SURFACE THROUGH 
THE ISTHMUS OF TEHUANTEPEC.

TRADE WINDS... 
THE ASCAT PASS FROM AROUND 1800 UTC SHOWED EASTERLY TRADES TO 25 
KT ACROSS A LARGE PORTION OF THE FORECAST AREA N OF THE ITCZ TO 
25N 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 CONTRACT W.

$$
SCHAUER CLARK