000 AXPZ20 KNHC 302143 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 2205 UTC WED APR 30 2008 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2130 UTC. ...ITCZ... ITCZ AXIS IS CENTERED ALONG 05N79W TO 07N88W TO 06N96W TO 07N105W TO 09N115W TO 09N122W TO 06N132W TO 03N140W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION EXISTS FROM 03N-07N BETWEEN 79W-86W. SCATTERED MODERATE CONVECTION IS WITHIN 120 NM S OF THE AXIS BETWEEN 127W-130W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS N OF THE AXIS WITHIN 30 NM EITHER SIDE OF LINE 09N127W TO 07N132W. ...DISCUSSION... E OF 100W... MID/UPPER RIDGE COVERS JUST ABOUT THE ENTIRE AREA N OF 07N INCLUDING CENTRAL AMERICA AND THE FAR WESTERN CARIBBEAN SEA. THIS RIDGING IS TO THE SE OF A BROAD MID/UPPER LEVEL TROUGH THAT EXTENDS FR0M THE NW GULF S TO ACROSS THE GULF OF TEHUANTEPEC AND TO A BASE NEAR 13N97W. THE FLOW PATTERN BETWEEN BOTH OF THESE FEATURES IS CONFLUENT AS DEPICTED BY MODERATE TO STRONG WINDS SW IN THE SATELLITE-DERIVED WINDS. THIS FLOW CONTINUES TO TRANSPORT AMPLE UPPER LEVEL DEBRIS CLOUDINESS FROM THE CONVECTION OCCURRING FROM 03N-07N BETWEEN 79W-86W N AND NE TOWARDS CENTRAL AMERICA AND NEWD INTO THE SW CARIBBEAN SEA. OVER THE SW PORTION OF THIS AREA...MODERATE SUBSIDENCE IS NOTED WITH VERY LIMITED CONVECTION. SOME INCREASE IN UPPER LEVEL MOISTURE...FROM THE CONVECTION STATED ABOVE...IS NOTED S OF 06N BETWEEN 85W-89W. ONLY ISOLATED SHOWERS ARE NOTED HERE. NWP MODELS ARE IN FAIR AGREEMENT THAT LOW PRES WILL LINGER IN THE VICINITY OF THE ITCZ OVER THE FAR E PORTION NEAR THE COAST OF NRN COSTA RICA. THIS MAY ALLOW FOR CONVECTION TO REMAIN RATHER ACTIVE OVER THIS SAME AREA ESPECIALLY IF RIDGING IN THE UPPER LEVELS CHANGES LITTLE AS GFS MODEL IS PORTRAYING. NLY WINDS OF 20 KT EARLIER OBSERVED THE GULF OF TEHUANTEPEC SHOULD DIMINISH SHORTLY. W OF 100W... A RATHER SHARP MID/UPPER LEVEL TROUGH EXTENDS FROM NRN BAJA CALIFORNIA SW TO 28N122W TO 27N130W THEN BECOMES A SHEAR AXIS TO 25N136W TO 21N140W. NW UPPER LEVEL FLOW IS CHANNELING SEWD INTO THE BACK SIDE OF THE TROUGH ALLOWING FOR FLOW PATTERN TO BE CONFLUENT THERE AND CREATING MODERATE SUBSIDENCE WITH ASSOCIATED DRY SINKING AIR NW OF A LINE FROM 29N115W TO 26N126W TO 22N140W. THE TROUGH IS FORECAST TO PUSH INLAND THE WESTERN UNITED STATES OVER THE NEXT FEW DAYS AS ANOTHER TROUGH SWINGS SEWD INTO SRN CALIFORNIA WITH AN EVENTUAL CUT-OFF LOW FORMING THERE...THEN LIFTING NEWD ACROSS THE SW UNITED STATES TUE AND WED IN ADVANCE OF UPPER LEVEL RIDGING THAT BUILDS EWD ACROSS THE NRN PORTION OF THE AREA. GFS SHOWS ANOTHER CUT-OFF LOW MOVING INTO THE FAR WRN PART OF THE AREA SUN AND MON...AND ALSO LIFTING NEWD AND BECOMING ABSORBED INTO A BROAD LONGWAVE TROUGH ON WED BEHIND THE FIRST LOW THAT MOVES ACROSS THE SW UNITED STATES. AT THE SURFACE...A STATIONARY 1032 MB HIGH CENTER N OF THE AREA NEAR 36N138W...EXTENDS A RIDGE SEWD THROUGH 30N132W TO 26N124W TO 22N117W TO 17N109W. HIGH PRES COVERS THE AREA N OF 15N AND W OF 108W. THE RIDGING...IN COMBINATION WITH LOW PRES OVER THE WRN UNITES STATES...IS CREATING A TIGHT PRES GRADIENT ALONG THE CALIFORNIA WITH STRONG NORTHERLY WINDS OBSERVED THERE...AND THAT ARE FUNNELING SE ALONG THE NRN BAJA COAST. THESE WINDS ARE FORECAST TO DIMINISH GRADUALLY OVER THE NEXT 2-3 DAYS AS THE RIDGE WEAKENS SLIGHTLY. A SURFACE TROUGH MOVING W 10-15 KT IS ALONG 122W FROM 06N-11N. THIS TROUGH MAY BE A REFLECTION OF A MID/UPPER TROUGH THAT EXTENDS FROM 20N140W SE TO A DEVELOPING CUT-OFF A MID/UPPER LEVEL LOW NEAR 06N129W. CONVECTION WITH THIS TROUGH IS PRETTY MUCH NON-EXISTENT WITH ONLY ISOLATED SHOWERS AND TSTMS WITHIN 45 NM OF 11N121W. FRESH TRADE WIND FLOW IS EXPECTED TO SHIFT S AS SURFACE HIGH TO THE NORTH SHIFTS SE PROVIDING BETTER LOW LEVEL CONVERGENCE. IN ADDITION SOME UPPER DIVERGENCE REMAINS IN PLACE ON SOUTHEAST SIDE OF UPPER TROUGH ...SO SOME INCREASE IN CONVECTION IS POSSIBLE IN THIS AREA OVER THE NEXT COUPLE OF DAYS. ANOTHER SURFACE TROUGH IS NOTED FURTHER WEST ALONG THE ITCZ NEAR 133W...AT THE SOUTHEAST BASE OF THE UPPER TROUGH. CONVECTION...AS STATED ABOVE UNDER ITCZ...IS OCCURRING OVER THE NRN PERIPHERY OF THIS TROUGH. $$ AGUIRRE