000 AXPZ20 KNHC 202205 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 2205 UTC SAT DEC 20 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 2145 UTC. ...ITCZ... ITCZ AXIS IS CENTERED ALONG 8N86W 5N93W 8N110W 10N123W 8N131W 6N1140W. SCATTERED MODERATE CONVECTION IS WITHIN 120 NM S OF THE AXIS BETWEEN 113W-117W. ...DISCUSSION... AN OMEGA BLOCKING PATTERN MAINTAINS CONTROL OF THE EASTERN PACIFIC DEFINED BY FIRST A MID/UPPER LEVEL CYCLONIC CIRCULATION THAT HAS BEEN CLEARLY EVIDENT OVER THE PAST SEVERAL OVER THE WESTERN PORTION OF THE AREA IS NOTED NEAR 21N135W MOVING WSW AROUND 20 KT. TO THE NE OF THIS CIRCULATION...A BROAD LONGWAVE TROUGH HAD MOVED INLAND OVER THE CENTRAL U.S. WITH ITS SOUTHERN TIER AXIS STRETCHING SW ACROSS SOUTHERN CALIFORNIA...AND INTO THE AREA NEAR 32N120W...SW TO A COL REGION NEAR 31N127W...THEN SW TO THE MID/UPPER LEVEL CYCLONIC CIRCULATION. A TROUGH EXTENDS S FROM THE CIRCULATION CENTER TO 13N135W AND SW TO 09N137W. STRONG NLY UPPER LEVEL FLOW CONTINUES TO SPILL AROUND THE E SIDE OF THE RIDGE AND TO W OF THE CYCLONIC CIRCULATION AS CONFLUENT FLOW BRINGING MODERATE SUBSIDENCE AND ASSOCIATED DRY AIR INTO THE CIRCULATION PORTION CONSISTING OF THE SW SEMICIRCLE OF THE LOW. THIS MID/UPPER LEVEL CYCLONIC CIRCULATION IS FORECAST TO CONTINUE ON A WESTWARD TRACK THROUGH THE NEXT 36-48 HOURS THEN MORE TO THE SW AFTERWARDS...CROSSING 140W NEAR 20N LATE MON NIGHT. THIS WILL BE IN RESPONSE TO A NW TO SE RIDGE CREST TO ITS E SHIFTING W IN TANDEM WITH IT. STRONG S TO SW FLOW ALOFT E OF THE MID/UPPER LEVEL CIRCULATION BETWEEN 110W AND 130W IS NOTED CHANNELING ABUNDANT MID AND UPPER LEVEL MOISTURE FROM THE ITCZ NE TOWARDS BAJA CALIFORNIA... NORTHERN MEXICO AND THE SW UNITED STATES. UPPER LEVEL DIVERGENCE WITHIN THIS UPPER LEVEL FLOW PATTERN AS NOTED IN THE CIMSS GUIDANCE...WITH THE ADDITIONAL AID OF A WEAK SURFACE TROUGH ALONG 121W/122W FROM 9N-15N IN COMBINATION WITH PERSISTENT EASTERLY FLOW IN THE TROPICAL ZONE IN ALREADY UNSTABLE ENVIRONMENT IS RESULTING IN AMPLE SURFACE MOISTURE CONVERGENCE...AND IN THE ASCENT OF THIS MOISTURE WHICH IS LEADING TO THE INITIALIZATION OF ADDITIONAL SCATTERED MODERATE/ISOLATED STRONG CONVECTION WITHIN AN AREA BOUNDED FROM 15N-19N BETWEEN 121W-125W. LATEST GLOBAL MODEL GUIDANCE SUGGESTS THAT THIS TROUGH FEATURE OR EVEN A WEAK SURFACE LOW WILL MOVE WNW OVER THIS AREA DURING THE NEXT 48 HOURS WITH ATTENDANT MOISTURE AREA AND CONVECTION TRANSLATING WESTWARD WITH THE TROUGH. THE PRES GRADIENT BETWEEN SURFACE HIGH PRES CENTERED NEAR 32N129W AND THE SURFACE TROUGH ALONG 121W/122W CONTINUES TO MAINTAIN A BROAD SWATH OF 20 TO 25 KT NE-E WINDS FROM 14N-28N BETWEEN 121W-130W AND FROM 8N-22N W OF 130W. THESE WINDS HAVE BEEN OCCURRING WITHIN A RATHER LONG DURATION SO SEAS IN THAT AREA HAVE INCREASED TO 8-13 FT IN MAINLY N SWELL WITH NE WIND WAVES. THIS AREA OF WINDS AND SEAS SHOULD TRANSLATE WESTWARD OVER THE NEXT 2 DAYS AS SURFACE HIGH PRES TO ITS E ALSO SHIFTS W. TIGHT PRES GRADIENT OVER THE NE PORTION SUPPORTING N-NE WINDS OF 20-25 KT WITH SEAS TO 8 FT WILL DIMINISH IN ABOUT 24 HOURS AS HIGH PRES OVER THE E PART OF THE AREA SHIFTS W. THE GRADIENT BETWEEN HIGH PRES BUILDING S FROM THE WESTERN U.S. INTO NORTHERN MEXICO AND RELATIVE TO LOW PRES TO THE S IS RESULTING IN NW 20 TO OCCASIONALLY 25 KT WINDS IN THE GULF OF CALIFORNIA. WITH A LIMITED FETCH WIDTH...SEAS OF 4 TO 7 FT ARE EXPECTED S OF 30N IN THE GULF OF CALIFORNIA DURING THE NEXT 48 HOURS. WINDS AND SEAS SHOULD BEGIN TO DIMINISH AND SUBSIDE THEREAFTER ONCE THE PRES EQUALIZES OVER THE REGION. PATCHES OF SCATTERED TO BROKEN STRATOCUMULUS CLOUDS WITH ISOLATED SHOWERS MOVING SW ARE NOTED TO THE N OF 15N AND W OF 119W. GAP WINDS... N-NE WINDS OF 20 KT THROUGH THE GULF OF TEHUANTEPEC AND PAPAGAYO ARE EXPECTED TO DIMINISH TO LESS THAN 20 KT WITHIN THE NEXT 24-48 HOURS...WHILE N WINDS TO 20 KT IN THE GULF OF PANAMA WILL DIMINISH TO LESS THAN 20 KT IN ABOUT 18 HOURS. $$ AGUIRRE