000
AXPZ20 KNHC 161556
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SAT AUG 16 2008

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

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1530 UTC.

...SPECIAL FEATURE...
TROPICAL DEPRESSION ISELLE 18.6N 112.3W MOVE NORTH-NORTHWEST AT 
5 KNOTS AT 1500 UTC.  MAXIMUM SUSTAINED WIND 30 TO 40 KT.  
SCATTERED MODERATE TO STRONG CONVECTION CURRENTLY FLARING WITHIN 
90 NM TO THE WEST OF THE CENTER IS ENOUGH TO MAINTAIN ISELLE AS 
A TROPICAL CYCLONE. ISELLE WEAKENING RAPIDLY DUE TO ITS COOLING 
SEA SURFACE TEMPERATURES AND INCREASED ELY WIND SHEAR ALOFT.  
SEE LATEST NHC FORECAST/ ADVISORY UNDER AWIPS/WMO HEADER 
MIATCMEP5/ WTPZ25 KNHC FOR MORE DETAILS.

...TROPICAL LOW...
LOW 15N121W 1011 MB STATIONARY. SCATTERED MODERATE TO STRONG 
CONVECTION IS NOTED WITHIN 60 NM TO THE WEST OF THE CENTER 
CURRENTLY...BUT FURTHER DEVELOPMENT IS NOT EXPECTED DUE TO 
PERSISTENT EASTERLY SHEAR.

...TROPICAL WAVES...
TROPICAL WAVE ALONG 112W FROM 05N TO 14N MOVE W 15 KT CONTINUES 
UNDER MODERATE ELY WIND SHEAR ALOFT WITH NO SIGNIFICANT 
ASSOCIATED CONVECTION.  DEVELOPMENT IS NOT EXPECTED.

TROPICAL WAVE ALONG 103W/104W FROM 06N TO 15N MOVING W 10 TO 15 
KT. THE WAVE IS LOSING DEFINITION AS IT ENTERS AN AREA OF LIGHT 
TO MODERATE WESTERLY SURFACE WINDS...AS DEPICTED BY A 1245Z 
QUIKSCAT PASS. THE WESTERLY WINDS ARE THE GENERAL FLOW ON THE 
SOUTH SIDE OF TROPICAL DEPRESSION ISELLE AND THE LOW AS 
DESCRIBED ABOVE. THE CLOSEST CONVECTION TO THE WAVE IS AN AREA 
ABOUT 240 NM EAST...AND UPSHEAR...OF THE WAVE...WHERE WEST AND 
SOUTHWEST WINDS ARE CONVERGING WITH EASTERLY TRADES. 

...ITCZ...
ITCZ AXIS IS ALONG THE LINE...09N84W TO 07N95W TO 11N110W TO 
09N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION FROM 04N 
TO 09N BETWEEN 80W AND 85W AND WITHIN 90-120 NM OF THE AXIS 
BETWEEN 92W AND 95W...AND BETWEEN 99W AND 104W. SCATTERED 
MODERATE CONVECTION WITHIN 120 NM OF THE AXIS BETWEEN 115W AND 
125W. 

...DISCUSSION...
EAST OF 110W...MORNING VISIBLE SATELLITE IMAGERY ALONG WITH 
QUIKSCAT DATA SHOW MODERATE TO FRESH CROSS-EQUATORIAL SOUTH TO 
SOUTHWEST FLOW MAINLY EAST OF 100W AND SOUTH OF THE ITCZ. THIS 
FLOW IS CONVERGING WITH WEST FLOW SOUTH OF T.D. ISELLE...THEN 
CONVERGING WITH NORTHEAST AND EAST TRADES TO MAINTAIN LARGE 
CLUSTERS OF CONVECTION ALONG THE ITCZ AS NOTED ABOVE. THE 
DOMINANT UPPER FEATURE REMAINS AN UPPER ANTICYCLONE CENTERED 
OVER NORTH CENTRAL MEXICO. THIS IS PROVIDING THE MODERATE DEEP 
LAYER EASTERLY SHEAR ACROSS THE AREA...MAINLY N OF 10N BETWEEN 
90W AND 110W...WEAKENING TROPICAL DEPRESSION ISELLE AS IT SLOWLY 
SHIFTS WEST AND DISSIPATES. LITTLE CHANGE IS EXPECTED IN THE 
FORECAST THROUGH SUNDAY. MEANWHILE...WAVEWATCH III IS INDICATING 
LONG PERIOD SOUTHERLY SWELL OF UP TO 15 S WITH HEIGHTS TO 4 FT 
WILL MOVE TO THE EAST OF THE GALAPAGOS REACHING THE COSTA RICAN 
AND WESTERN PANAMA COASTS TONIGHT BEFORE DECAYING SUNDAY.

WEST OF 110W...AN UPPER TROUGH FROM 30N131W TO 21N128W BREAKS UP 
AN UPPER RIDGE EXTENDING FROM AN ANTICYCLONE OVER NORTH CENTRAL 
MEXICO TO ANOTHER UPPER ANTICYCLONE CENTERED NEAR 20N137W. 
MODERATE EASTERLY SHEAR PERSISTS SOUTH OF THE UPPER RIDGES 
ACROSS THE AREA S OF 20N. CONVECTION ASSOCIATED THE TROPICAL LOW 
NEAR 15N121W IS IN AN AREA OF RELATIVELY WEAK SHEAR NEAR WHERE 
THE UPPER TROUGH BREAKS UP THE RIDGE AXIS. THIS SHEAR WILL 
INCREASE AND INHIBIT THE CONVECTION LATER TODAY AND TONIGHT AS 
THE UPPER TROUGH LIFTS OUT OF THE AREA TO THE NORTHEAST...AND 
THE UPPER RIDGE BUILDS. LIGHT TO MODERATE SOUTHERLY FLOW INTO 
THE ITCZ IS SUPPORTING MODEST CLUSTERS OF LIGHT CONVECTION...BUT 
OVERALL DEEP LAYER MOISTURE REMAINS LIMITED MANLY W OF 120W.

$$
CHRISTENSEN