000
AXPZ20 KNHC 180318
TWDEP 

TROPICAL WEATHER DISCUSSION                                    
NWS NATIONAL HURRICANE CENTER MIAMI FL                           
0405 UTC THU JUL 18 2013

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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0300 UTC.

...TROPICAL WAVES...                                            
A TROPICAL WAVE EXTENDS FROM 19N109W TO 12N110W. SCATTERED 
MODERATE TO ISOLATED STRONG CONVECTION IS NOTED MAINLY AHEAD OF 
THE WAVE AXIS FROM 12N TO 16N BETWEEN 110W AND 115W...AND 
ELSEWHERE FROM 10N TO 14N BETWEEN 108W AND 113W. THE WAVE 
COINCIDES WITH A BULGE OF MOISTURE PRESENT IN TOTAL PRECIPITABLE 
WATER IMAGERY. GLOBAL MODELS ARE IN FAIR AGREEMENT INDICATING 
THE WAVE WILL DAMPEN OUT AS IT TRACKS FARTHER WEST THROUGH THE 
NEXT COUPLE OF DAYS.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...        
MONSOON TROUGH EXTENDS FROM 09N84W TO 08N93W TO 13N109W TO 
10N122W. ITCZ CONTINUES FROM 10N122W TO 11N132W...THEN RESUMES 
AT 10N138W TO BEYOND 09N140W. A CLUSTER OF MODERATE TO STRONG 
CONVECTION IS SEEN FROM 05N TO 08N BETWEEN 82W AND 85W. 
CONVECTION HAS INCREASED OVER COSTA RICA AND REGIONAL WATERS... 
PARTICULARLY FROM 09N TO 11N E TO 87W AND OVER THE GULF OF 
FONSECA. SCATTERED MODERATE CONVECTION CAN BE FOUND FROM 07N TO 
15N W OF 127W IN ASSOCIATION WITH THE ITCZ AND EMBEDDED SURFACE 
TROUGH. 

...DISCUSSION...                                               
ALOFT...AN ANTICYCLONE LOCATED WEST OF AREA NEAR 12N145W EXTENDS 
A RIDGE NE ACROSS THE WEST-CENTRAL WATERS TO ABOUT 23N129W.  
MODERATE TO STRONG SUBSIDENCE AND IMPLIED DRY AIR MASS COVERS 
MOST OF THE AREA N OF 16N W OF 122W. AN UPPER TROUGH EXTENDS 
FROM AN UPPER LOW CENTERED NEAR 26N125W TO 15N129W. THE UPPER 
LOW AND TROUGH WILL LARGELY LOSE DEFINITION AND DAMPEN OUT OVER 
THE NEXT 24 HOURS AHEAD OF AN AMPLIFYING UPPER TROUGH LOCATED N 
OF THE HAWAIIAN ISLANDS WHICH IS ALREADY PRODUCING MODERATE SW 
FLOW ACROSS THE NW CORNER OF THE AREA. A RIDGE DOMINATES WESTERN 
MEXICO...THE BAJA CALIFORNIA PENINSULA AND THE WATERS N OF 18N E 
OF 120W. MODERATE TO STRONG SOUTHERLY WINDS ARE NOTED BETWEEN 
THE UPPER LOW AND THE ANTICYCLONE. AN INVERTED TROUGH EXTENDS 
FROM 17N116W TO 10N113W. EASTERLY WINDS ALOFT DOMINATE MUCH OF 
THE AREA N OF 05N E OF 110W. UPPER DIFFLUENCE IS SUPPORTING THE 
MODERATE TO STRONG CONVECTION PREVIOUSLY MENTIONED OVER WESTERN 
PANAMA...COSTA RICA AND THE PACIFIC REGIONAL WATERS.  

THE MAIN MARINE IMPACT WILL BE THE BRIEF POTENTIAL FOR NE WINDS 
OF 20 TO 25 KT AND SEAS TO 9 FT AHEAD OF A SURFACE TROUGH THAT 
CURRENTLY EXTENDS FROM 15N134W TO 10N137W. THE MOST RECENT ASCAT 
PASS SHOWED NE WINDS OF 15-20 KT AHEAD OF THE TROUGH AXIS. 
SCATTERED MODERATE CONVECTION IS NOTED ON EITHER SIDE OF TROUGH 
AXIS. PRES GRADIENT BETWEEN THE TROUGH AND HIGH PRES TO THE 
NORTH WILL BRING AN INCREASE IN THE AERIAL EXTENT OF THE FRESH 
TO STRONG NE WINDS ASSOCIATED WITH THIS TROUGH LATER TONIGHT 
INTO THU. THESE MARINE CONDITIONS WILL SHIFT W OF 140W ALONG 
WITH THE TROUGH THU NIGHT.

A SURGE OF TRADE WINDS OVER THE CARIBBEAN SEA WILL PUSH GAP 
WINDS TO 20 KT THROUGH THE GULF PAPAGAYO THU MORNING AND FRI 
MORNING. THIS ALONG WITH SOME ASSISTANCE FROM A TROPICAL WAVE 
MOVING INTO THE WESTERN CARIBBEAN AND SOUTHERN CENTRAL AMERICA  
WILL ALLOW FOR A WEAK SURFACE LOW PRES AREA TO FORM ALONG THE 
MONSOON TROUGH OFF THE COAST OF COSTA RICA OVER THE NEXT 48 
HOURS. GLOBAL MODELS CARRY THE LOW WESTWARD...REACHING 95W BY  
SAT AND NEAR 99W BY SUN WITH AN EXPECTED CENTRAL PRESSURE AROUND 
1009 MB. FOR NOW...THE MAIN IMPACT WILL BE AN INCREASE IN SHOWER 
AND TSTM ACTIVITY OVER THE WATERS E OF 100W. 

A STRONG UPPER LEVEL LOW SPINNING OVER NEW MEXICO IS EXPECTED TO 
EVENTUALLY PUSH SW INTO THE GULF OF CALIFORNIA FRI INTO SAT. 
THIS WILL ENHANCE SURFACE TROUGHING OVER THE GULF AND BAJA...AND 
ITS INTERACTION WITH RIDGING TO THE WEST WILL RESULT IN FRESH NW 
WINDS OFF THE NORTHERN COAST OF BAJA CALIFORNIA BY LATE THU... 
WITH SEAS BUILDING TO 8 FT. THE UPPER LOW WILL WEAKEN FRI AND 
SAT ALLOWING WINDS AND SEAS TO DIMINISH.

LONG PERIOD CROSS EQUATORIAL SOUTHWESTERLY SWELLS RESULTING IN 
COMBINED SEAS TO 8 FT DOMINATE THE FORECAST WATERS S OF LINE 
FROM 00N92W TO 10N105W TO 10N112W TO 00N128W. A SET OF LONG 
PERIOD SW SWELLS...WAVE PERIOD OF 19 TO 21 SECONDS...IS NOW 
REACHING MOST OF THE MEXICAN COAST AND WILL AFFECT MOST OF THE 
COAST OF CENTRAL AMERICA LATER TONIGHT...BRINGING ROUGH SURF 
CONDITIONS AND DANGEROUS RIP CURRENTS TO THOSE COASTS. 
  
$$ 
GR