000
AXPZ20 KNHC 180952
TWDEP 

TROPICAL WEATHER DISCUSSION   
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SAT JUN 18 2011

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS 
BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND 
METEOROLOGICAL ANALYSIS.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0945 UTC.

...SPECIAL FEATURES...
A BROAD AREA OF LOW PRESSURE CONTINUES OVER THE PACIFIC WATERS S 
OF THE MEXICAN AND GUATEMALA BORDER...AND IS CURRENTLY ANALYZED 
AS AN 1007 MB SURFACE LOW NEAR 12N95W...ALONG AN E TO W TROUGH 
ALONG 12N BETWEEN 92W AND 98W EVIDENT ON CURRENT ASCAT DATA. 
ISOLATED MODERATE AND STRONG CONVECTION IS FLARING WITHIN ABOUT 
150 NM OF THE CENTER. MODEL GUIDANCE SUGGESTS GRADUAL 
DEVELOPMENT OF THIS SURFACE LOW OVER THE NEXT SEVERAL DAYS AS IT 
DRIFTS WEST...WITH THE POSSIBILITY OF TROPICAL CYCLONE 
FORMATION. SOUTHERLY WINDS WILL INCREASE TO THE S OF THIS 
SURFACE LOW TO THE EQUATOR OVER THE NEXT FEW DAYS.   
  
...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH EXTENDS FROM 12N86W TO THE 1008 MB LOW PRES 
AT 12N96W...THEN CONTINUES W ALONG 11N TO 118W...THEN TURNS SW 
TO 08N127W WHERE LOW LEVEL WINDS INDICATE THE ITCZ BEGINS AND 
CONTINUES W TO BEYOND 06N140W. LOCALLY OVERCAST LOW AND MID 
LEVEL CLOUDS ARE NOTED OVER THE ENTIRE AREA N OF THE EQUATOR TO 
THE E OF 100W...AND FROM 05N TO THE MEXICAN COAST BETWEEN 100W 
AND 107W. ISOLATED EMBEDDED CLUSTERS OF MODERATE AND STRONG 
CONVECTION ARE NOTED N OF 03N E OF 90W...AND FROM 05N TO 17N 
BETWEEN 90W AND 107W. ONLY A FEW THUNDERSTORMS ARE NOTED ALONG 
THE MONSOON TROUGH BETWEEN 107W AND 127W. ISOLATED MODERATE 
CONVECTION IS OBSERVED NEAR 07N126W AND WITHIN 30 NM OF THE ITCZ 
AXIS BETWEEN 132W AND 139W. 

...DISCUSSION...
AN UPPER TROUGH EXTENDS SW FROM SOUTHERN CALIFORNIA TO 30N121W 
INTO AN UPPER CYCLONE AT 23N136W...WITH THE UPPER TROUGH THEN  
CONTINUING SW TO BASE OVER THE TROPICS AT 15N141W. UPPER 
MOISTURE ACCOMPANIES THE UPPER TROUGH WITHIN 150 NM NW OF THE 
DESCRIBED TROUGH AXIS. VERY DRY UPPER AIR IS INDICATED WITHIN 
180 NM SE OF THE TROUGH AXIS...AND OVER THE REMAINDER OF THE 
DISCUSSION AREA TO THE N OF 10N AND TO THE W OF 120W. 

A SMALL UPPER CYCLONE IS NOTED NEAR THE EQUATOR AT 131W. AN 
UPPER ANTICYCLONE IS QUASI STATIONARY OVER CENTRAL OLD MEXICO AT 
24N104W WITH ITS ENVELOPE OF ANTICYCLONIC FLOW DOMINATING MOST 
THE DISCUSSION AREA BETWEEN 90W AND 125W. AN UPPER RIDGE EXTENDS 
SW TO A CREST AT 08N133W...WITH A SMALL AREA OF UPPER DIFFLUENCE 
EXISTING W OF THE RIDGE OVER THE ITCZ W OF 132W...AND IS 
SUPPORTING THE PREVIOUSLY DESCRIBED CONVECTION. THE ASSOCIATED 
DEBRIS MOISTURE IS FANNING OUT FROM 03N TO 10N BETWEEN 133W AND 
143W. OTHERWISE THE UPPER LEVELS APPEAR DRY S OF 08N BETWEEN 
110W AND 130W...AND IS SUPPRESSING CONVECTION IN THE SAME AREA. 
THE UPPER ANTICYCLONE IS EXPECTED TO WEAKEN SOME THIS WEEKEND AS 
AN UPPER TROUGH MOVES S OVER NORTHERN OLD MEXICO.   
 
AN UPPER TROUGH EXTENDS SW ACROSS THE SE GULF OF MEXICO TO A 
BASE OVER THE MEXICO AND GUATEMALA BORDER NEAR 10.5N106W. 
AN UPPER LEVEL ANTICYLONE IS OVER THE SW CARIBBEAN RESULTING IN 
BROAD RIDGING...AND UPPER DIFFLUENCE...OVER THE TROPICAL PACIFIC 
E OF 110W. ENHANCED CONVECTION HAS RESULTED IN DEEP LAYERED 
MOISTURE...WITH CONVECTION IS LIKELY TO CONTINUE TO FLARE IN THE 
AREA S OF 18N E OF 108W FOR THE NEXT DAY OR SO.

ELSEWHERE AT THE LOW LEVELS...A BROAD RIDGE COVERS THE AREA N OF 
THE 10N TO THE W OF 118W. AS THE RIDGE SHIFTS EASTWARD TONIGHT 
INTO SUN...THE GRADIENT WILL INCREASE THE NORTHWESTERLY LOW 
LEVEL FLOW ALONG THE PACIFIC SIDE OF THE BAJA CALIFORNIA 
PENINSULA BRIEFLY TO 20 KT. THE NE FLOW WILL ALSO BRIEFLY 
INCREASE TO THE SW OF THE RIDGE IN THE AREA N OF 23N W OF 133W 
ON SUN.

$$
NELSON