000 AXPZ20 KNHC 161553 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 1605 UTC THU MAY 16 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 1545 UTC. ...SPECIAL FEATURE... TROPICAL STORM ALVIN IS CENTERED NEAR 9.4N 107.7W AT 16/1500 UTC MOVING WNW AT 8 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1003 MB. MAXIMUM SUSTAINED WIND SPEED IS 45 KT WITH GUSTS TO 55 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP1/WTPZ21 KNHC FOR MORE DETAILS. NUMEROUS MODERATE TO STRONG CONVECTION IS WITHIN 210 NM OF THE CENTER IN THE SE QUADRANT. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 120 NM OF THE CENTER IN THE NE QUADRANT...AND ALSO WITHIN 60 NM OF THE CENTER IN THE NW QUADRANT. ALVIN HAS WEAKENED DURING THE MORNING IS HAS COME UNDER THE INFLUENCE OF VERTICAL SHEAR AS NOTED BY THE UPPER LEVEL FLOW PATTERN ON WATER VAPOR IMAGERY. GUIDANCE INDICATES THAT THE SHEAR WILL ONLY CONTINUE TO AFFECT ALVIN OVER THE NEXT FEW DAYS. ALVIN IS NOW FORECAST TO REMAIN A TROPICAL STORM WITH A STEADY INTENSITY OF ABOUT 50 KT THROUGH THE NEXT 48 HRS AS TRACKS WNW. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH AXIS EXTENDS FROM 07N76W TO LOW PRES NEAR 07N78W 1009 MB TO 07N1101W...THEN RESUMES FROM 08N110W TO 06N131W...THEN ITCZ TO 06N140W. SCATTERED STRONG CONVECTION IS NOTED WITHIN 180 NM OF THE AXIS BETWEEN 110W-117W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 90 NM OF THE AXIS BETWEEN 120W-126W...WITHIN 180 NM N OF THE AXIS BETWEEN 130W- 137W...AND ALSO N OF 05N E OF 81W. SCATTERED MODERATE CONVECTION EXISTS WITHIN 150 NM S OF THE AXIS BETWEEN 91W AND 95W. ...DISCUSSION... ALOFT...WATER VAPOR IMAGERY SHOWS A SWATH...ABOUT 720 NM WIDE...OF MODERATE TO STRONG SUBSIDENCE COVERING THE AREA FROM 29N TO 17N. A JET STREAM BRANCH IS NOTED ALONG 17N W OF 126W... AND STRETCHES NE FROM 126W AT 18N TO ACROSS SRN BAJA CALIFORNIA AND WELL INLAND CENTRAL MEXICO. S OF THIS JET STREAM ABUNDANT UPPER LEVEL MOISTURE IS SEEN STREAMING ENE FROM THE DEEP TROPICAL CENTRAL PACIFIC REGION. THIS MOISTURE IS FURTHER ENHANCED FROM UPPER LEVEL DEEP CLOUDINESS DUE TO THE VERY COLD CLOUD TO CONVECTION ASSOCIATED WITH THE MONSOON AND ITCZ FEATURES AS WELL AS THAT RELATED TO TROPICAL STORM ALVIN. AT THE SURFACE...A HIGH CENTER OF 1027 MB IS LOCATED JUST NW OF THE AREA AT 31N144W...WHILE ANOTHER HIGH CENTER OF 1022 MB IS WELL N OF THE AREA AT 40N140W. A RIDGE ROUGHLY ALONG 32N W OF 124W. HIGH PRES COVERS THE AREA N OF 16N W OF ABOUT 115W. ELSEWHERE A WEAK PRES PATTERN REMAINS IN PLACE. MODELS INDICATE THAT RIDGE WILL STRENGTHEN OVER THE NEXT 48 HRS INDUCING A SLIGHTL TIGHTER PRES GRADIENT OVER A PORTION OF THE SW PART OF THE AREA. THIS SHOULD ALLOW FOR NE-E TRADE WINDS OF 20 KT FROM 13N-18N AND W OF ABOUT 136W...WITH SEAS MAXING OUT TO 8-9 FT PRIMARILY DUE TO A SW SWELL COMPONENT ORIGINATING FROM THE SRN HEMISPHERE. WEAK LOW PRES IS ANALYZED ALONG THE MONSOON TROUGH AT 07N78W. THIS FEATURE WILL CONTINUE TO ENHANCE CYCLONIC WINDS IN THE GULF OF PANAMA THROUGH EARLY TONIGHT. THE LOW IS EXPECTED TO MOVE NNW ACROSS THE ISTHMUS OF PANAMA THROUGH FRI MORNING AND WEAKEN. WITH RESPECT TO MARINE ISSUES...LONG PERIOD SW SWELLS MOVING FROM THE SRN HEMISPHERE...AS STATED ABOVE...WILL MIX WITH SWELLS GENERATED BY ALVIN AND PRODUCE SEAS GREATER THAN 8 FT IN EQUATORIAL WATERS BETWEEN 99W AND 121W OVER THE NEXT 48 HRS. $$ AGUIRRE