000 AXPZ20 KNHC 170954 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 1005 UTC SAT APR 17 2010 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0945 UTC. ...ITCZ... THE ITCZ AXIS EXTENDS ALONG 05N BETWEEN 77W AND 140W. SCATTERED MODERATE IS OBSERVED FROM 06N TO 11N BETWEEN 84W AND 94W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS OBSERVED WITHIN 240 NM OF 03N120W...30 NM OF 03N125W...60 NM OF 06N131W AND FROM 05N TO 11N BETWEEN 133W AND 136W. ...DISCUSSION... A COMPLEX UPPER LEVEL CYCLONE DOMINATES THE THE NE PACIFIC WITH A DEEP LAYERED CYCLONE NEAR 30N145W SPAWNING SEVERAL SURFACE CYCLONES AS IT APPROACHES THE NW CORNER OF THE DISCUSSION AREA. A BAND OF DRY UPPER AIR HAS SHIFTED N OF 30N E OF 135W. AN UPPER LEVEL ANTICYCLONE IS QUASI STATIONARY NEAR 11N126W WITH AN UPPER RIDGE EXTENDING W TO BEYOND 11N140W...WITH BROAD ANTICYCLONIC CIRCULATION DOMINATING THE REMAINDER OF THE UPPER LEVELS W OF 112W. ITCZ CONVECTION WAS ENHANCED EARLIER UNDER THE RIDGE FROM 110W TO 138W. SOME OF THE DEBRIS MOISTURE IS SPREADING S ACROSS THE EQUATOR BETWEEN 120W AND 135W. BUT SOME OF THE MOISTURE IS NOW ADVECTED NW ALONG THE WESTERN RIDGE TO NEAR 15N140W...WHERE IT MERGES WITH A MORE PRONOUNCED TROPICAL PLUME THAT ORIGINATES OVER THE DEEP TROPICAL CENTRAL PACIFIC. THE COMBINED PLUME CONTINUES NE ACROSS THE DISCUSSION AREA ALONG THE PERIPHERY OF THE LARGE UPPER RIDGE...ROUGHLY WITHIN 360 NM EITHER SIDE OF LINE 18N140W TO 25N125W TO 26N115W TO 19N105W WHERE THE MOISTURE EVAPORATES. HOWEVER SOME OF THE MOISTURE SPLITS OFF THE PLUME CYCLONICALLY AROUND AN UPPER TROUGH OVER SOUTHERN CALIFORNIA AND SPREADS N OVER NEW MEXICO. A DEEP LAYERED CYCLONE OVER N CENTRAL TEXAS HAS AN UPPER TROUGH EXTENDING SSE OVER EASTERN OLD MEXICO ALONG 23N96W TO A BASE OVER THE TROPICAL PACIFIC COAST OF CENTRAL AMERICA NEAR 13N90W. THERE IS NOW EVIDENCE OF THE TROUGH CONTINUING S INTO ANOTHER UPPER CYCLONE NEAR 06N96W. AN UPPER RIDGE EXTENDS W FROM S AMERICA OVER THE DEEP TROPICS TO A CREST ESTIMATED AT 10N95W. VERY DRY UPPER AIR IS INDICATED UNDER THE UPPER RIDGE FROM 10N TO 17N E OF 130W AND INTO THE UPPER TROUGH. DIFFLUENCE E OF THE UPPER TROUGH ENHANCED CONVECTION WITH THE DEBRIS MOISTURE SPREADING NE ACROSS THE GULF OF MEXICO. ITCZ CONVECTION IS ENHANCED JUST E OF THE UPPER TROUGH...AND UNDER THE W END OF THE TROPICAL RIDGE...ROUGHLY FROM 05N TO 11N E OF 95W. THE RESULTANT DEBRIS MOISTURE IS ADVECTED NE ACROSS CENTRAL AMERICA TO THE E OF 88W. ALL OF THIS DEBRIS MOISTURE HAS THE UPPER LEVELS OF THE TROPICS QUITE MOIST FROM MEXICO TO THE BAHAMAS. AT THE SURFACE...HIGH PRES OF 1020 MB IS CENTERED AT 28N124W AND IS BEGINNING TO SHIFT N. THIS WILL ALLOW THE APPROACHING LOW PRES AND ASSOCIATED COLD FRONT TO ADVANCE FURTHER E INTO THE DISCUSSION AREA...PERHAPS TO ALONG 120W...THAN THE PREVIOUS COLD FRONT. THE PRESSURE GRADIENT BETWEEN THE RIDGE AND THE NEXT FRONT WILL INCREASE AGAIN TO 20 TO 30 KT. THE GRADIENT W OF THE FRONT WILL ALSO INCREASE TO 20 TO 30 KT...PERHAPS A MINIMAL GALE JUST W OF THE AREA...AND DRIVE SEAS TO ABOUT 15 FT INTO AREA. NOTE THIS IS SLIGHTLY BELOW GUIDANCE WHICH SUGGESTS SEAS TO 17 FT. FURTHER S...NE TRADES OF 20 KT ARE OBSERVED FROM 08N TO 15N BETWEEN 112W AND 130W WITH THIS AREA OF TRADES EXPECTED TO RELAX TO LESS THAN 20 KT AS THE PARENT HIGH PRESSURE SHIFTS N THROUGH 48 HOURS. REMNANT SEAS ABOVE 8 FT WILL PERSIST OVER THE TROPICS W OF 90W IN MIXED NE...NW AND EVEN SW SWELL THROUGH ANOTHER 48 HOURS. THE PRESSURE GRADIENT BETWEEN THE AFOREMENTIONED SURFACE HIGH PRESSURE...AND A TROUGH OVER THE SIERRA MADRE OCCIDENTAL...IS PRODUCING NW SURGES TO 20 KT WITHIN 180 NM W OF THE NORTHERN BAJA PENINSULA...EXPECTED TO PERSIST THROUGH TONIGHT THEN DIMINISH BELOW 20 KT SUN. $$ NELSON