000
AXPZ20 KNHC 181518
TWDEP 

TROPICAL WEATHER DISCUSSION                                      
NWS NATIONAL HURRICANE CENTER MIAMI FL                           
1605 UTC SAT MAY 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1330 UTC.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...             
THE REMNANTS OF ALVIN ARE EMBEDDED IN THE MONSOON TROUGH AXIS 
NEAR 12N116W. NUMEROUS MODERATE TO STRONG CONVECTION WAS BETWEEN 
60 NM AND 180 NM OF ITS E QUADRANT. SCATTERED MODERATE WITH 
ISOLATED STRONG CONVECTION WAS ELSEWHERE FROM 07N TO 16N BETWEEN 
111W AND 118W. 

THE MONSOON TROUGH AXIS EXTENDS FROM 09N78W TO 10N89W TO 06N102W 
TO THE REMNANTS OF ALVIN TO 10N120W TO 09N123W. THE ITCZ AXIS 
EXTENDS FROM 09N123W TO 08N131W TO 04N140W. SCATTERED MODERATE 
TO STRONG CONVECTION WAS WITHIN 90 NM S OF THE AXIS BETWEEN 86W 
AND COSTA RICA. SCATTERED MODERATE WITH ISOLATED STRONG 
CONVECTION WAS WITHIN 45 NM N AND 150 NM S OF THE AXIS BETWEEN 
93W AND 103W. SCATTERED MODERATE CONVECTION WAS WITHIN 60 NM N 
OF THE AXIS BETWEEN 120W AND 123W AND WITHIN 180 NM N OF THE 
AXIS BETWEEN 123W AND 128W.

...DISCUSSION...                                                
THE 1007 MB REMNANTS OF ALVIN ARE CENTERED NEAR 12N116W. THIS 
LOW PRESSURE SYSTEM FELL BETWEEN SCATTEROMETER PASSES THIS 
MORNING AND DID NOT SEE AN ALTIMETER SWATH NEAR THE CENTER. 
WINDS TO 30 KT ARE BELIEVED TO LIE PRIMARILY E OF THE 
CENTER...WITH WINDS GREATER THAN 20 KT SPANNING THE AREA WITHIN 
210 NM NE SEMICIRCLE AND SE QUADRANT. SEAS ARE BELIEVED TO BE AS 
HIGH AS 11 FT UNDER THESE CONDITIONS...WITH CROSS-EQUATORIAL 
SOUTHWESTERLY SWELL KEEPING SEAS ABOVE 8 FT OVER A LARGE AREA S 
OF THE LOW BETWEEN 100W AND 126W...PRIMARILY S OF 05N. THE LOW 
IS EXPECTED TO CONTINUE ON A WESTWARD TRACK AT ABOUT 10 KT OVER 
THE NEXT FEW DAYS AS IT GRADUALLY WEAKENS. 20-25 KT WINDS WILL 
SHIFT TO THE N SEMICIRCLE BY MON AS THE LOW MOVES FROM THE SE 
SIDE OF THE SUBTROPICAL HIGH TO S OF THE HIGH.  

THE 1025 MB SUBTROPICAL HIGH WAS ANALYZED NEAR 35N137W WITH A 
RIDGE EXTENDING SE THROUGH 32N120W TO 30N125W TO 15N107W. A 
MODERATE NW BREEZE CONTINUES E OF THE RIDGE AXIS ALONG THE COAST 
OF BAJA CALIFORNIA N OF 26N ACCORDING TO THE 0420 UTC ASCAT-A 
PASS. WINDS ARE EXPECTED TO INCREASE OFF THE CALIFORNIA COAST 
SUN AND MON AS A COLD FRONT...CURRENTLY IMPINGING ON THE 
SUBTROPICAL HIGH FROM THE N...SWEEPS THROUGH THE OFFSHORE WATERS 
THERE. THE SUBTROPICAL HIGH IS EXPECTED TO SHIFT N OF THE FRONT 
SUN AND RIDGING WILL STRENGTHEN OVER N FORECAST WATERS. NW SWELL 
WILL TRAVEL S OF 32N BEGINNING EARLY SUN AND EXPAND TO WATERS N 
OF 27N BETWEEN 118W-128W BY MON MORNING. 

MODERATE TO FRESH TRADE WINDS WERE OBSERVED BY SUBSEQUENT 
ASCAT PASSES AND A WINDSAT PASS FROM 0246 UTC IN THE AREA N OF 
THE ITCZ TO ABOUT 20N. SEAS TO 9 FT WERE OBSERVED BY EARLIER 
ALTIMETER PASSES GENERALLY IN THE AREA FROM 06N-21N W OF 127W. 
WINDS WILL REMAIN BELOW ADVISORY CRITERIA HERE THROUGH THE 
FORECAST PERIOD AND SEAS GENERATED BY TRADE WIND FLOW WILL SHIFT 
W OF THE AREA BY SUN...BUT SEAS FROM THE REMNANTS OF ALVIN WILL 
QUICKLY MOVE INTO THE AREA LATE SUN INTO MON. 

AN AREA OF SCATTERED MODERATE TO STRONG CONVECTION ALONG THE 
COAST OF COSTA RICA IS NOTED IN THE SECTION ABOVE. THIS 
CONVECTION IS BEING ENHANCED BY SUPPER LEVEL DIVERGENCE BETWEEN 
20 KT EASTERLIES TO THE S AND 5-10 KT SOUTHEASTERLY WINDS TO THE 
N. MEANWHILE...AN AREA OF UPPER DIFFLUENCE BETWEEN SOUTHEASTERLY 
WINDS ON THE SW SIDE OF AN ANTICYCLONE NEAR ACAPULCO MEXICO AND 
A RIDGE AXIS ALONG 03S BETWEEN 90W-110W IS ENHANCING CONVECTION 
ALONG ITCZ BETWEEN 93W-103W. THIS AREA COINCIDES WITH THE 
HIGHEST PRECIPITABLE WATER VALUES OUTSIDE OF THE REMNANTS OF 
ALVIN WITHIN THE FORECAST AREA. FLOW ALOFT HERE SHOULD CONTINUE 
TO SUPPORT AN INCREASED CHANCE OF CONVECTION THROUGH THE END OF 
THE FORECAST PERIOD MON MORNING.

$$
SCHAUER