000 AXPZ20 KNHC 162139 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 2205 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2100 UTC. ...SPECIAL FEATURES... TROPICAL STORM ALVIN CENTERED NEAR 9.5N 109.1W AT 16/2100 UTC OR ABOUT 730 MI SSW OF MANZANILLO MEXICO MOVING WNW AT 10 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1005 MB. MAXIMUM SUSTAINED WIND SPEED IS 40 KT WITH GUSTS TO 50 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP1/WTPZ21. NUMEROUS MODERATE AND SCATTERED STRONG CONVECTION IS WITHIN 150 NM IN THE W SEMICIRCLE OF ALVIN...WITH SCATTERED MODERATE CONVECTION WITHIN 120 NM IN THE E SEMICIRCLE OF ALVIN. ALVIN HAS WEAKENED SLIGHTLY DURING THE PAST SEVERAL HOURS AS IT CONTINUES TO BE AFFECTED BY 20-25 KT OF WESTERLY SHEAR...AND IT IS UNLIKELY THAT THE SHEAR WILL ABATE DURING THE NEXT FEW DAYS. THUS THE OFFICIAL FORECAST NOW KEEPS ALVIN AT ITS CURRENT INTENSITY...40 KT...THROUGH LATE TONIGHT...THEN GRADUALLY WEAKENING TO A TROPICAL DEPRESSION BY SUN AFTERNOON...AND THEN TO A REMNANT LOW BY MON AFTERNOON. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH AXIS EXTENDS FROM 1011 MB LOW PRES NEAR 07N79W TO 09N87W TO 06N97W TO 09N104W...THEN RESUMES FROM 09N110W TO 05N134W. THE ITCZ AXIS EXTENDS FROM 05N134W TO 04N140W. SCATTERED MODERATE TO STRONG CONVECTION IS WITHIN 180 NM EITHER SIDE OF THE MONSOON TROUGH BETWEEN 110W AND 120W. SIMILAR CONVECTION IS WITHIN 75-120 NM EITHER SIDE OF THE MONSOON TROUGH BETWEEN 121W AND 131W. ...DISCUSSION... ALOFT...WATER VAPOR IMAGERY SHOWS A SWATH...OF ABOUT 660 NM WIDE...OF MODERATE TO STRONG SUBSIDENCE BETWEEN A LINE FROM 26N109W TO 17N140W AND ANOTHER LINE FROM 32N120W TO 27N140W. A JET STREAM BRANCH IS NOTED ALONG 16N W OF 120W...STRETCHING NE FROM 120W TO ACROSS SRN BAJA CALIFORNIA AND WELL INLAND OVER 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...RELATING TO TROPICAL STORM ALVIN. AT THE SURFACE...1028 MB HIGH PRES IS LOCATED JUST W OF THE DISCUSSION WATERS NEAR 31N145W...WITH A RIDGE EXTENDING TO THE E- SE THROUGH 27N130W TO NEAR 20N110W. MAINLY MODERATE ANTICYCLONIC WINDS AND 5-7 FT SEAS COVER THE WATERS N OF 13N W OF 110W UNDER THIS RIDGING. MODEL GUIDANCE INDICATES THAT THE RIDGE WILL STRENGTHEN OVER THE NEXT 48 HRS INDUCING A SLIGHTLY TIGHTER PRES GRADIENT OVER THE FAR W CENTRAL WATERS OF THE AREA...ALLOWING FOR NE-E TRADE WINDS OF 15-20 KT FROM 16N TO 19N W OF 136W BY LATE TONIGHT...THEN SHIFTING TO COVER THE WATERS FROM 13N TO 19N W OF 136W BY FRI AFTERNOON. SEAS OF 8-9 FT WILL ACCOMPANY THESE WINDS...COMBINED WITH LONG PERIOD SW SWELL. THE WINDS WILL THEN DIMINISH WITH SEAS SUBSIDING TO LESS THAN 8 FT BY SAT AFTERNOON AS THE PRES GRADIENT THEN SLACKENS. WEAK LOW PRES IS ANALYZED ALONG THE MONSOON TROUGH NEAR 07N79W...WITH ASSOCIATED SCATTERED MODERATE AND ISOLATED STRONG CONVECTION WITHIN 240 NM IN THE W SEMICIRCLE OF THE LOW. MODEL GUIDANCE HAS LOWERED WITH RESPECT TO THE STRENGTH AND ASSOCIATED WINDS WITH THIS LOW WHICH ARE ALREADY 20 KT OR LESS...AND A RECENT ALTIMETER PASS WHICH WENT RIGHT OVER THE AREA SHOWED THAT SEAS ARE NOW LESS THAN 8 FT. THE LOW IS FORECAST TO DRIFT TO THE NW-N DURING THE NEXT 24 HOURS. LONG PERIOD SW SWELLS MOVING UP FROM THE SRN HEMISPHERE WILL MIX WITH SWELLS GENERATED BY ALVIN...PRODUCING SEAS OF 8 FT OR GREATER IN THE EQUATORIAL WATERS BETWEEN 107W AND 120W DURING THE NEXT 48 HRS. $$ LEWITSKY