000
AXPZ20 KNHC 162158
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC SAT AUG 16 2008

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 
2030 UTC.

...SPECIAL FEATURE...
TROPICAL DEPRESSION ISELLE 18.4N 112.6W MOVING NORTH-NORTHWEST 
AT 3 KNOTS AT 2100 UTC. MAXIMUM SUSTAINED WIND 30 TO 40 KT.  
SCATTERED MODERATE TO STRONG CONVECTION CURRENTLY FLARING WITHIN 
240 NM IN THE NORTHWEST 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 WAVES...
TROPICAL WAVE ALONG 104W FROM 06N TO 15N MOVING SLOWLY W. THE 
WAVE CONTINUES TO LOSE DEFINITION AS IT ENTERS AN AREA OF LIGHT 
TO MODERATE WESTERLY SURFACE WINDS...AS DEPICTED BY A MORNING 
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...08N83W TO 10N102W TO 10N121W TO 
11N128W TO 09N140W.  SCATTERED MODERATE ISOLATED STRONG 
CONVECTION WITHIN 240 NM S OF AXIS E OF 88W.  SCATTERED MODERATE 
CONVECTION WITHIN 75 NM N AND 120 NM S OF AXIS FROM 120W TO 132W.

...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. A SURFACE TROUGH IS ANALYZED FROM 
15N117W TO 16N125W...WITH MODERATE CONVECTION WITHIN 60 NM ON 
EITHER SIDE OF THE AXIS. THIS 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