000 AXPZ20 KNHC 210348 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 0405 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 6N78W 6N92W 7N106W 10N120W 10N130W 7N1140W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 120 NM S OF THE AXIS BETWEEN 130W-134WW. SCATTERED MODERATE CONVECTION IS WITHIN 120 NM N OF THE AXIS BETWEEN 122W-130W. ...DISCUSSION... AN OMEGA BLOCKING PATTERN MAINTAINS CONTROL OF THE EASTERN PACIFIC DEFINED BY 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 W AT 15 KT. TO THE NE OF THIS CIRCULATION...A BROAD LONGWAVE TROUGH HAS MOVED INLAND OVER THE CENTRAL U.S. WITH THE SOUTHERN PORTION OF ITS AXIS STRETCHING SW ACROSS SOUTHERN CALIFORNIA...AND INTO THE AREA NEAR 32N118W...THEN WSW 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 TRACK MORE IN SW DIRECTION AFTER THAT TIME...CROSSING 140W NEAR 20N LATE MON NIGHT. THIS WILL BE IN RESPONSE TO A NW TO SE ORIENTED RIDGE THAT WILL SHIFT W IN TANDEM WITH IT. TO THE E OF THE ABOVE MENTIONED MID/UPPER LEVEL CYCLONIC CIRCULATION STRONG S TO SW FLOW ALOFT CONTINUES TO CHANNEL ABUNDANT MID AND UPPER LEVEL MOISTURE FROM THE ITCZ NORTHEASTWARDS TOWARDS BAJA CALIFORNIA...NORTHERN MEXICO AND THE SW UNITED STATES. UPPER LEVEL DIVERGENCE WITHIN THIS FLOW PATTERN AS NOTED IN THE CIMSS GUIDANCE...WITH THE ADDITIONAL AID OF A WEAK SURFACE TROUGH ROUGHLY ALONG 129W/130W FROM 9N-18N IN COMBINATION WITH PERSISTENT EASTERLY FLOW IN THE TROPICAL ZONE IN AN 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 45 NM EITHER SIDE OF A LINE FROM 16N127W TO 20N127W. SCATTERED MODERATE CONVECTION IS WITHIN 45 NM OF 13N120W. LATEST GLOBAL MODEL GUIDANCE SUGGESTS THAT THIS TROUGH FEATURE OR EVEN A WEAK SURFACE LOW ...WITH GFS GUIDANCE BEING THE MOST AGGRESSIVE...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 129W/130W CONTINUES TO MAINTAIN A BROAD SWATH OF 20 TO 25 KT NE-E WINDS FROM 15N-27N BETWEEN 121W-132W...AND ALSO FROM 10N-25N W OF 132W. THESE WINDS HAVE BEEN OCCURRING WITHIN A RATHER LONG DURATION ALLOWING FOR SEAS IN THAT AREA TO BUILD UP TO 12 OF 13 FT IN NOW AN E SWELL. THIS AREA OF WINDS AND SEAS SHOULD TRANSLATE WESTWARD OVER THE NEXT 2 DAYS WITH SURFACE HIGH PRES TO ITS E ALSO SHIFTING 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 KT WINDS IN THE GULF OF CALIFORNIA S OF 28N AT THE PRESENT TIME. WITH A LIMITED FETCH WIDTH...SEAS ARE FORECAST TO REMAIN LESS THAN 8 FT. THESE WINDS ARE EXPECTED TO DIMINISH TO LESS THAN 20 KT IN 48 HOURS...BUT THERE MAY BE A BRIEF INSTANCE OF WINDS REACHING SPEEDS HIGHER THAN 20 KT EVEN THOUGH MODEL GUIDANCE DOES NOT INDICATE SO. PATCHES OF SCATTERED TO BROKEN STRATOCUMULUS CLOUDS WITH ISOLATED SHOWERS MOVING SW ARE NOTED FROM 16N TO 28N W OF 121W. GAP WINDS... N-NE WINDS OF 20-25 KT ARE FORECAST TO BEGIN THROUGH THE GULF OF TEHUANTEPEC IN ABOUT 36 HOURS...THEN WEAKEN SOME IN 48 HOURS AS HIGH PRES OVER MEXICO IS NOT FORECAST TO BE THAT STRONG. NE WINDS TO 20 KT THROUGH THE GULF OF PAPAGAYO ARE EXPECTED TO DIMINISH TO LESS THAN 20 KT IN 18 HOURS...THEN INCREASE TO 20 KT IN 36 HOURS. $$ AGUIRRE 000 AXPZ20 KNHC 210348 RRA TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC SUN DEC 21 2008 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0330 UTC. ...ITCZ... ITCZ AXIS IS CENTERED ALONG 6N78W 6N92W 7N106W 10N120W 10N130W 7N1140W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 120 NM S OF THE AXIS BETWEEN 130W-134WW. SCATTERED MODERATE CONVECTION IS WITHIN 120 NM N OF THE AXIS BETWEEN 122W-130W. ...DISCUSSION... AN OMEGA BLOCKING PATTERN MAINTAINS CONTROL OF THE EASTERN PACIFIC DEFINED BY 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 W AT 15 KT. TO THE NE OF THIS CIRCULATION...A BROAD LONGWAVE TROUGH HAS MOVED INLAND OVER THE CENTRAL U.S. WITH THE SOUTHERN PORTION OF ITS AXIS STRETCHING SW ACROSS SOUTHERN CALIFORNIA...AND INTO THE AREA NEAR 32N118W...THEN WSW 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 TRACK MORE IN SW DIRECTION AFTER THAT TIME...CROSSING 140W NEAR 20N LATE MON NIGHT. THIS WILL BE IN RESPONSE TO A NW TO SE ORIENTED RIDGE THAT WILL SHIFT W IN TANDEM WITH IT. TO THE E OF THE ABOVE MENTIONED MID/UPPER LEVEL CYCLONIC CIRCULATION STRONG S TO SW FLOW ALOFT CONTINUES TO CHANNEL ABUNDANT MID AND UPPER LEVEL MOISTURE FROM THE ITCZ NORTHEASTWARDS TOWARDS BAJA CALIFORNIA...NORTHERN MEXICO AND THE SW UNITED STATES. UPPER LEVEL DIVERGENCE WITHIN THIS FLOW PATTERN AS NOTED IN THE CIMSS GUIDANCE...WITH THE ADDITIONAL AID OF A WEAK SURFACE TROUGH ROUGHLY ALONG 129W/130W FROM 9N-18N IN COMBINATION WITH PERSISTENT EASTERLY FLOW IN THE TROPICAL ZONE IN AN 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 45 NM EITHER SIDE OF A LINE FROM 16N127W TO 20N127W. SCATTERED MODERATE CONVECTION IS WITHIN 45 NM OF 13N120W. LATEST GLOBAL MODEL GUIDANCE SUGGESTS THAT THIS TROUGH FEATURE OR EVEN A WEAK SURFACE LOW ...WITH GFS GUIDANCE BEING THE MOST AGGRESSIVE...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 129W/130W CONTINUES TO MAINTAIN A BROAD SWATH OF 20 TO 25 KT NE-E WINDS FROM 15N-27N BETWEEN 121W-132W...AND ALSO FROM 10N-25N W OF 132W. THESE WINDS HAVE BEEN OCCURRING WITHIN A RATHER LONG DURATION ALLOWING FOR SEAS IN THAT AREA TO BUILD UP TO 12 OF 13 FT IN NOW AN E SWELL. THIS AREA OF WINDS AND SEAS SHOULD TRANSLATE WESTWARD OVER THE NEXT 2 DAYS WITH SURFACE HIGH PRES TO ITS E ALSO SHIFTING 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 KT WINDS IN THE GULF OF CALIFORNIA S OF 28N AT THE PRESENT TIME. WITH A LIMITED FETCH WIDTH...SEAS ARE FORECAST TO REMAIN LESS THAN 8 FT. THESE WINDS ARE EXPECTED TO DIMINISH TO LESS THAN 20 KT IN 48 HOURS...BUT THERE MAY BE A BRIEF INSTANCE OF WINDS REACHING SPEEDS HIGHER THAN 20 KT EVEN THOUGH MODEL GUIDANCE DOES NOT INDICATE SO. PATCHES OF SCATTERED TO BROKEN STRATOCUMULUS CLOUDS WITH ISOLATED SHOWERS MOVING SW ARE NOTED FROM 16N TO 28N W OF 121W. GAP WINDS... N-NE WINDS OF 20-25 KT ARE FORECAST TO BEGIN THROUGH THE GULF OF TEHUANTEPEC IN ABOUT 36 HOURS...THEN WEAKEN SOME IN 48 HOURS AS HIGH PRES OVER MEXICO IS NOT FORECAST TO BE THAT STRONG. NE WINDS TO 20 KT THROUGH THE GULF OF PAPAGAYO ARE EXPECTED TO DIMINISH TO LESS THAN 20 KT IN 18 HOURS...THEN INCREASE TO 20 KT IN 36 HOURS. $$ AGUIRRE