000 AXPZ20 KNHC 181605 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 1605 UTC WED MAR 18 2009 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1545 UTC. ...ITCZ... ITCZ AXIS IS CENTERED ALONG 3N79W TO 4N92W TO 2N110W TO 3N130W 6N104W. NO SIGNIFICANT CONVECTION IS NOTED. ...DISCUSSION... N OF 20N... A RATHER PROGRESSIVE UPPER LEVEL PATTERN IS EVIDENT ACROSS THE REGION WITH FIRST FEATURE NOTED BEING A SHORTWAVE TROUGH THAT EXTENDS FROM N OF THE AREA NEAR 27N135W SW TO A WEAK UPPER LEVEL CYCLONIC CIRCULATION MOVING NE NEAR 32N134W. THE TROUGH CONTINUES SE TO NEAR 22N128W. A MID/UPPER LEVEL RIDGE IS E OF THE TROUGH...AND LIES ROUGHLY ALONG 26N122W TO N OF THE AREA AT 32N122W. A SMALLER SHORTWAVE TROUGH...DAMPENING OUT WITH TIME ...IS E OF THIS RIDGE JUST ALONG THE NORTHERN BAJA CALIFORNIA AND STRETCHING N TO ALONG THE SOUTHERN CALIORNIA COAST. IT IS MOVING INLAND. THE FLOW PATTERN TO THE W OF THE TROUGH IS ZONAL AS A STRONG JET STREAM STRETCHES W TO E ALONG 21N BETWEEN 130W AND 140W. LATEST GLOBAL MODEL GUIDANCE SUGGESTS THAT AN AMPLIFYING SHORTWAVE TROUGH WILL DIVE SOUTHEASTWARD TOWARDS 30N BY THE END OF THE WEEK ALLOWING FOR A WEAKENING COLD FRONT TO MOVE THROUGH THE FAR NORTHERN WATERS. THIS FRONT SHOULD BRING A SHORT-LIVED PERIOD OF N WINDS TO ABOUT 20 KT OVER THESE WATERS WITH WAVEWATCH GUIDANCE INDICATING SEAS TO BUILD UP TO 10 FT OR 11 FT IN MAINLY A NW SWELL. THESE SWELLS WILL THEN SLOWLY SUBSIDE TO 8 FT GOING INTO SAT. AT THE SURFACE...A 1027 MB HIGH IS N OF THE AREA NEAR 34N132W. ITS IS FORECAST TO MOVE SW TO NEAR 32N135W AS A 1025 MB IN 24 HOURS. S OF 20N... A MID/UPPER LEVEL TROUGH EXTENDS FROM 16N118W TO 10N118W TO S OF THE EQUATOR AT 117W. UPPER LEVEL DIVERGENCE TAKING PLACE FROM 6N TO 15N BETWEEN 120W AND 127W IS SETTING OFF ISOALTED MODERATE CONVECTION WITHIN 45 NM OF 12N125W...AND ISOLATED SHOWERS ESLEWHERE ELSEWHERE WITHIN THIS AREA. THE TROUGH IS CAUGHT IN BETWEEN TWO AREAS OF BROAD MID/UPPER LEVEL RIDGING IS OBSERVED ON WATER VAPOR IMAGERY. EXTENSIVE MID/UPPER LEVEL MOISTURE IN THE FORM OF OVERCAST TO BROKEN MOSTLY BLOW OFF CIRRUS CLOUDS IS NOTED OVER THE FAR WESTERN SECTION OF THE AREA FROM 7N TO 20N W OF 135W. SCATTERED SHOWERS AND ISOLATED TSTMS ARE OCCURRING UNDER THESE CLOUDS. AT SURFACE...NE-E WINDS OF GENERALLY 15 KT ARE SEEN HERE WHILE LIGHTER WINDS ARE JUST S NEAR AND ALONG THE ITCZ. THIS IS ALSO SUPPOTRING DEVELOPEMNT OF SHOWERS AND TSTMS IN THIS AREA. THIS AREA WILL LIKELY REMAIN CONVECTIVELY ACTIVE FOR ANOTHER 24 HOURS AS THE UPPER LEVEL DYNAMICS AND DIVERGENCE SHIFT EWD. A 1028 MB SURFACE HIGH WAS CENTERED N OF THE AREA NEAR 34N131W...WITH THE ENHANCED SURFACE PRESSURE GRADIENT AT THE SOUTHERN PERIPHERY OF THIS FEATURE ENHANCING NE TO E TRADES ACROSS THE REGION...AND CONTRIBUTING TO THE BROAD LOW LEVEL CONVERGENCE ZONE DISCUSSED ABOVE. OLD NWLY SWELL CONTINUES TO PROPAGATE THROUGH MOST OF THE FORECAST AREA THIS MORNING...WITH HIGHEST SEAS NEAR 11 FT LOCATED WITHIN THIS BAND OF ENHANCED NE TO E TRADES...IN A MIX OF NW AND SW SWELL AND NELY WIND WAVES. AS THE UPPER FLOW N OF THE AREA AMPLIFIES...THE SURFACE HIGH IS EXPECTED TO WEAKEN DURING THE NEXT FEW DAYS. IN RESPONSE...TRADE WINDS WILL SLACKEN...WITH SEAS GRADUALLY SUBSIDING. GAP WINDS... GULF OF TEHUANTEPEC WINDS HAVE DIMINISHED TO 20 TO 25 KT...AND EXPECETD TO DIMINISH TO LESS THAN 20 KT IN 36 HOURS...THEN INCREASE AGAIN TO 20 TO 25 KT IN 48 HOURS. NATEPEC SURFACE HIGH PRESSURE BUILDING SOUTHWARD OVER EASTERN MEXICO IN THE WAKE OF A FRONT OVER THE GULF OF MEXICO IS SUPPORTING A RELATIVELY STRONG SURFACE PRESSURE GRADIENT ACROSS THE ISTHMUS OF TEHUANTEPEC...WITH STRONG N TO NE WINDS FUNNELING INTO THE GULF OF TEHUANTEPEC. COMPUTER MODEL GUIDANCE AND RECENT SCATTEROMETER PASSES INDICATE THAT WINDS IN THIS REGION HAVE DIMINISHED BELOW GALE FORCE...BUT WERE STILL IN THE 20-30 KT RANGE PRIOR TO 06Z. THUS THE GALE WARNING FOR THE GULF OF TEHUANTEPEC HAS EXPIRED. ALSO...TRADE WINDS ACROSS THE CARIBBEAN CONTINUE WITH A PERSISTENT SURFACE LOW OVER NW COLOMBIA. THESE WINDS CONTINUE TO BLEED INTO THE GULFS OF PANAMA AND PAPAGAYO. GAP WINDS OF AROUND 20 KT IN THE GULFS OF TEHUANTEPEC AND PAPAGAYO ARE FORECAST TO CONTINUE PERIODICALLY DURING THE NEXT FEW DAYS...WITH THE STRONGEST WINDS EXPECTED LATE AT NIGHT WHEN DRAINAGE FLOW OFF HIGHER TERRAIN IS MAXIMIZED IN THE PRESENCE OF DEEP LAYER DRY AIR. HOWEVER...WINDS IN THE GULF OF PANAMA ARE EXPECTED TO FLUCTUATE AROUND 20 KT THROUGH 24 HOURS BEFORE DIMINISHING BY 48 HOURS...WHEN THE SURFACE RIDGING OVER THE CARIBBEAN WEAKENS AND THE SURFACE LOW OVER NW COLOMBIA FILLS. $$ AGUIRRE