000
AXPZ20 KNHC 180954
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC TUE AUG 18 2009

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

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0930 UTC.

...TROPICAL WAVES...

A TROPICAL WAVE IS ANALYZED N OF 06N ALONG 96W WITH WESTWARD 
MOTION OF 15 KT OVER THE PAST 48 HOURS. SLIGHT CYCLONIC TURNING 
IS NOTED ALONG THE WAVE AXIS AT 11N WHERE A SMALL CLUSTER OF 
TSTMS...VERIFIED BY LIGHTNING DATA...IS NOTED.

A TROPICAL WAVE IS ANALYZED N OF 06N ALONG 109W AND HAS BEEN 
MOVING W AT 15 KT OVER THE PAST 72 HOURS. ISOLATED MODERATE AND 
STRONG CONVECTION IS NOTED WITHIN 90 NM E OF THE WAVE AXIS 
FROM07N TO 09N.

A TROPICAL WAVE IS ANALYZED FROM 04N TO 16N ALONG 125W AND HAS 
BEEN MOVING W AT NEARLY 15 KT OVER THE PAST 72 HOURS. SCATTERED 
MODERATE ISOLATED STRONG CONVECTION IS FLARING FROM 08N TO 14N 
WITHIN 180 NM E OF THE WAVE AXIS.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE WAS ANALYZED ALONG 08N78W TO 
10N95W TO 09N110W TO 10N125W TO 07N140W. SCATTERED MODERATE 
ISOLATED STRONG CONVECTION IS NOTED FROM 04N TO 11N TO THE E OF 
110W AND FROM 06N TO 13N BETWEEN 117W AND 136W. 

SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED NO F THE 
ITCZ AXIS WITHIN 90 NM OF THE CENTRAL AMERICAN COAST BETWEEN 81W 
AND 86W AND ALSO FURTHER N WITHIN 120 NM OF THE COAST FROM 93W 
TO 106W.

...DISCUSSION...

AN UPPER LEVEL ANTICYCLONE IS CENTERED AT 27N132W WITH A RIDGE 
EXTENDING SW TO A SHARP CREST AT 16N146W. A RIDGE ALSO EXTENDS 
NE TO 30N127W. SOME DEBRIS MOISTURE FROM ITCZ CONVECTION BETWEEN 
133W AND 143W IS ADVECTED N ALONG THE W PERIPHERY OF RIDGE 
BETWEEN 135W AND 140W AND IS WRAPPING NE TO NEAR 31N130W WHERE 
IT EVAPORATES. 

A SECOND UPPER ANTICYCLONE HAS MOVED OFF OLD MEXICO TO NEAR 
25N112W WITH ITS ENVELOPE OF ANTICYCLONIC FLOW DOMINATING THE 
AREA N OF 11N BETWEEN 111W AND 121W. DEBRIS MOISTURE FROM ITCZ 
CONVECTION BETWEEN 119W AND 130W IS ADVECTED N ALONG THE W 
PERIPHERY OF RIDGE BETWEEN 116W AND 121W.
 
SQUEEZED BETWEEN THE UPPER ANTICYCLONES IS A WELL DEFINED UPPER 
CYCLONE AT 19N126W WITH A TROUGH EXTENDING S TO 11N128W. DRY 
UPPER AIR IS INDICATED WITHIN ROUGHLY 300 NM EITHER SIDE OF LINE 
16N132W TO 32N120W WHERE IT MERGES WITH A BAND OF UPPER DRY AIR 
THAT IS SPREADING E ACROSS THE UPPER LEVELS OF THE WESTERN 
CONUS.

AN UPPER CYCLONE IS NOTED NEAR 19N100W WITH A TROUGH EXTENDING S 
ACROSS OLD MEXICO OVER THE TROPICAL PACIFIC TO A BASE AT 07N100W.
BROAD UPPER RIDGING IS ENHANCING CONVECTION OVER THE TROPICAL 
PACIFIC ELSEWHERE E OF 95W WITH THE DEBRIS MOISTURE REMAINING IN 
ROUGHLY THE SAME AREA OR EVAPORATING BEFORE CROSSING THE 
EQUATOR.   

AT LOW LEVELS A SURFACE RIDGE EXTENDS INTO THE AREA AT 32N138W 
TO 10N112W. NW WINDS ARE EXPECTED TO PULSE AT MOSTLY 15 BUT 
OCCASIONALLY 20 KT ALONG THE W COAST OF THE BAJA PENINSULA FOR 
A COUPLE OF DAYS. SOUTHERLY WINDS TO THE S OF THE ITCZ AREA 
EXPECTED IN THE 15 TO 20 KT RANGE WITH SEAS REACHING A MAX OF 8 
FT. 

LONG PERIOD SOUTHERLY SWELLS OF UP TO 6 TO 7 FT AT 12 TO 14 
SECONDS ARE EXPECTED TO REACH THE COAST OF CENTRAL AMERICA S OF 
THE BAJA PENINSULA THU NIGHT...WITH 18 PERIOD SWELLS REACHING 
SOUTHERN CALIFORNIA LATE FRI.

$$
NELSON