000
AXPZ20 KNHC 081007
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC FRI AUG 08 2008

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 
0945 UTC.

...SPECIAL FEATURE...

TROPICAL STORM HERNAN IS CENTERED NEAR 15.0N 118.9W AT 0900 UTC 
MOVING W AT 11 KT. MAXIMUM SUSTAINED WINDS ARE 55 KT WITH GUSTS 
TO 65 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 994 MB. HERNAN 
IS EXPERIENCING NE WIND SHEAR WITH THE LOW LEVEL CENTER NOTED TO 
THE N OF AN INTERMITTENT MID LEVEL OPEN CENTER. SCATTERED 
MODERATE TO STRONG CONVECTION IS NOTED WITHIN 60 NM N AND WITHIN 
90 NM W...BUT WITHIN 150 NM ELSEWHERE OF CENTER. HERNAN IS 
EXPECTED TO STRENGTHEN TO A HURRICANE TODAY THEN WEAKEN TO A 
TROPICAL STORM AGAIN ON SAT AFTER ENCOUNTERING COOLER WATER. SEE 
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADER 
MIATCMEP4/WTPZ24 KNHC FOR MORE DETAILS.

...TROPICAL WAVES... 

A TROPICAL WAVE IS ALONG 81W IN THE E PAC AND HAS BEEN MOVING W 
AT ABOUT 12 KT THE PAST 24 HOURS. CONVECTION IS FLARING OVER 
CENTRAL AMERICA AND THE TROPICAL PAC CONSIDERABLY W OF THE WAVE 
AXIS...FROM 04N TO 10N BETWEEN 82W AND 88W.   

A TROPICAL WAVE IS ALONG 105W FROM 05N TO 16N MOVING W AT ABOUT 
15 KT THE PAST 24 HOURS. SCATTERED MODERATE ISOLATED STRONG 
CONVECTION IS NOTED WITHIN 150 NM EITHER SIDE OF THE WAVE AXIS 
FROM 06N TO 15N. BROAD CYCLONIC TURNING IS ALSO NOTED.

A TROPICAL WAVE ALONG 135W FROM 5N TO 15N HAS MOVED W AT 12 KT 
THE PAST 24 HOURS. SCATTERED MODERATE ISOLATED STRONG CONVECTION 
IS NOTED FROM 09N TO 14N W OF THE WAVE AXIS TO 140W. 

...ITCZ...

THE ITCZ AXIS IS ALONG 08N82W TO 10N194W TO 13N110W TO 13N119W 
TO 11N125W TO 09N140W. SCATTERED MODERATE ISOLATED STRONG 
CONVECTION IS NOTED FROM 04N TO 10N BETWEEN 82W AND 88W AND ALSO 
WITHIN 150 NM EITHER SIDE OF LINE FROM 08N88W TO 08N98W TO 
13N109W...AND ALSO WITHIN 120 NM EITHER SIDE OF LINE FROM 
11N117W TO 11N140W.

...DISCUSSION...

A SLIGHTLY NEGATIVE TILT LONGWAVE UPPER LEVEL TROUGH LIES OVER 
THE NE PACIFIC ALONG ROUGHLY 137W...AND EXTENDS S INTO THE 
DISCUSSION AREA FROM 32N128W TO 19N140W. A REINFORCING SHORTWAVE 
TROUGH IS SWINGING SE INTO THE AREA ALONG 32N130W TO 26N140W. 
DRY UPPER AIR IS INDICATED W OF LINE 32N128W TO 16N140W. 

AN UPPER LEVEL ANTICYCLONE IS CENTERED NEAR 25N118W WITH A RIDGE 
EXTENDING N TO NEAR 31N115W. AN UPPER RIDGE ALSO EXTENDS SW TO A 
SHARP CREST AT 14N136W. THE ENVELOPE OF UPPER ANTICYCLONIC FLOW 
EXTENDS S TO ALONG 14N BETWEEN 113W AND THE RIDGE AXIS...AND 
OVER TROPICAL STORM HERNAN. UPPER DIFFLUENCE IS ENHANCING 
HERNANS CONVECTION AND ITCZ CONVECTION BETWEEN 114W AND 140W 
WITH THE DEBRIS MOISTURE REMAINING S OF 18N...BUT SOME OF THE 
MOISTURE IS ADVECTED S ACROSS THE EQUATOR BETWEEN 130W AND 140W. 
UPPER DRY AIR IS INDICATED UNDER THE RIDGE FROM 20N TO 31N 
BETWEEN 115W AND 123W. AT THE LOW LEVELS A RIDGE EXTENDS FROM 
30N140W TO 23N115W. LOCALLY BROKEN STRATOCUMULUS IS NOTED N OF 
18N W OF 116W.  

AN ATLC UPPER TROUGH EXTENDS SW ACROSS THE NW CARIBBEAN FROM 
21N81W TO 13N90W AND THEN CONTINUES SW ACROSS THE EQUATOR AT 
100W. TO THE NW OF THIS TROUGH...AN ILL-DEFINED UPPER 
ANTICYCLONE IS ESTIMATED NEAR 21N96W WITH WEAK ANTICYCLONIC FLOW 
NOTED ALONG THE COAST OF CENTRAL AMERICA BETWEEN 95W AND 105W. 
TO THE SE OF THE UPPER TROUGH...A BROAD UPPER RIDGE EXTENDS W 
ALONG 10N TO NEAR 85W. DEBRIS MOISTURE FROM CONVECTION DESCRIBED 
ABOVE IS OBSERVED OVER THE TROPICS E OF 110W.   

GAP WINDS...FRESH NE WINDS OVER THE W CARIBBEAN ARE SURGING 
ACROSS CENTRAL AMERICA INTO...AND WITHIN 420 NM DOWNSTREAM OF 
THE GULF OF PAPAGAYO AT 20 KT.  LITTLE CHANGE EXPECTED FOR LEAST 
A COUPLE OF DAYS.

$$
NELSON