000
AXPZ20 KNHC 310256
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC FRI JUL 31 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 
0230 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 99W N OF 04N MOVING W NEAR 20 KT OVER THE 
PAST 24 HOURS. CONVECTION IS MINIMAL NEAR THE WAVE AXIS AT THIS 
TIME. THE WAVE IS EMBEDDED IN MODERATE EASTERLY FLOW ALOFT TO 
THE N OF AN INVERTED TROUGH LOCATED SW OF THE WAVE AND AN UPPER 
LEVEL RIDGE AXIS TO ITS N. 

TROPICAL WAVE IS ALONG 121W FROM 06N TO 18N MOVING W NEAR 10 KT 
OVER THE PAST 24 HOURS. SCATTERED MODERATE ISOLATED STRONG 
CONVECTION WAS NOTED WITHIN 240 NM W OF THE WAVE AXIS FROM 09N 
TO 13N. A CLUSTER OF SCATTERED STRONG CONVECTION WAS NOTED AT 
THE NORTHERN END OF THE WAVE WITHIN 60 NM OF 16N120W. THIS 
CONVECTION LIES IN THE UPPER LEVEL DIFFLUENT REGION ON THE 
EASTERN SIDE OF AN UPPER LEVEL LOW NEAR 13N127W.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE IS ALONG THE LINE...08N83W TO 
09N97W TO 07N108W TO 12N120W TO 10N140W. SCATTERED MODERATE 
ISOLATED STRONG WITHIN 120 NM EITHER SIDE OF AXIS BETWEEN 115W 
AND 132W...AND WITHIN 90 NM EITHER SIDE OF THE AXIS BETWEEN 103W 
AND 113W. SCATTERED MODERATE WITHIN 90-120 NM OF THE AXIS 
BETWEEN 87W AND 95W. 

...DISCUSSION...

A MID LEVEL CIRCULATION WAS EVIDENT IN VISIBLE AND INFRARED 
SATELLITE IMAGERY NEAR 10N90W WILL MOVE WESTWARD OVER THE NEXT 
48 HOURS AND SLOWLY DEVELOP AS IT TRACKS ALONG WITH A REGION OF 
MODERATE UPPER LEVEL DIFFLUENCE. CURRENTLY...THE MAJORITY OF THE 
CONVECTION IN THE EASTERN PACIFIC ASSOCIATED WITH THE SYSTEM 
LIES WITHIN 90-120 NM EITHER SIDE OF THE ITCZ AXIS BETWEEN 87W 
AND 95W. LOW LEVEL VORTICITY IS FORECAST TO BE ENHANCED AS IT 
ENCOUNTERS THE CROSS EQUATORIAL SOUTHERLY FLOW IN THE FAR 
EASTERN PACIFIC AND THE EASTERLY GAP WINDS FROM PAPAGAYO WITH 
THE POTENTIAL FOR THE DEVELOPMENT OF A SURFACE LOW WITHIN 48 
HOURS. SEE THE DISCUSSION ON GAP WINDS BELOW FOR DETAILS ON THE 
GULF OF PAPAGAYO WINDS.

THE NEXT ROUND OF SOUTHWESTERLY SWELL WILL BE CROSSING THE 
EQUATOR OVER THE NEXT 24 HOURS. SIGNIFICANT WAVE HEIGHTS ARE 
ALREADY AROUND 8 FT IN SE SWELL S OF 08N BETWEEN 116W AND 126W. 
THE SW SWELL MOVES INTO THE REGION LATE TODAY WITH LONGER PERIOD 
SW SWELL ENCROACHING ON THIS GENERAL REGION IN THE S CENTRAL 
PORTION OF THE FORECAST AREA ON SAT. THIS ROUND OF SWELLS IS NOT 
EXPECTED TO HAVE THE IMPACT OF THE SWELL EVENT LAST WEEKEND. 

SURFACE HIGH PRESSURE AND GENERALLY SUBSIDENT CONDITIONS WITH 
WIDESPREAD STRATOCUMULUS CLOUDS DOMINATES THE REGION N OF 20N W 
OF 120N AND FROM 20N120W TO THE CENTRAL BAJA CALIFORNIA 
COAST.

GAP WINDS...
A HIGH RESOLUTION ASCAT PASS FROM 1720 UTC INDICATED SE WINDS IN 
THE NORTHERN GULF OF CALIFORNIA OF 20-25 KT. THIS FLOW APPEARS 
TO BE DRIVEN BY THE TIGHTENED PRESSURE GRADIENT BETWEEN LOW 
PRESSURE OVER INTERIOR SOUTHERN CALIFORNIA AND HIGH PRESSURE 
OVER NW MEXICO. THIS PRESSURE GRADIENT IS STRONGEST WITH 
AFTERNOON HEATING. MODEL GUIDANCE SHOWS THIS PRESSURE GRADIENT 
WEAKENING OVER THE NEXT 24 HOURS...ALLOWING THESE WINDS TO 
DIMINISH BELOW 20 KT BY FRI MORNING.

THE 1210 UTC HIGH RESOLUTION QUIKSCAT PASS SHOWED NE TO E WINDS 
IN THE 20 TO 25 KT RANGE DOWNWIND OF THE GULF OF PAPAGAYO. THESE 
WINDS ARE EXPECTED TO MODERATE ALONG WITH THE TRADE WIND FLOW IN 
THE SW CARIBBEAN OVER THE NEXT 24 HOURS...BUT AS THE LOW PRES 
SYSTEM NEAR PANAMA PUSHES WEST OF THE GULF OF PAPAGAYO ON 
SATURDAY EXPECT THE WINDS TO TRACK EAST AWAY FROM THE GULF AND 
THE FLOW ASSOCIATED WITH THE LOW TO INCREASE TO 20 KT ON ITS 
NORTHERN SIDE.

$$
COBB