000 AXPZ20 KNHC 190944 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 1005 UTC WED SEP 19 2012 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0945 UTC. ...SPECIAL FEATURES... TROPICAL DEPRESSION LANE IS CENTERED AT 20.8N 130.9W AT 0900 UTC MOVING W-NW OR 290 DEG AT 8 KT. MAXIMUM SUSTAINED WINDS ARE 30 KT WITH GUSTS TO 40 KT AND A MINIMUM PRESSURE OF 1009 MB. CURRENTLY ONLY A SINGLE CLUSTER OF MODERATE CONVECTION IS DISSIPATING WELL NE OF THE EXPOSED CENTER...WITHIN 30 NM OF 23N128W. LANE IS MOVING OVER RELATIVELY COOL SURFACE WATERS AND IS FORECAST TO WEAKEN TO A REMNANT LOW LATER TODAY. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP2/WTPZ22 KNHC FOR ADDITIONAL DETAILS. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS WESTWARD ACROSS THE GULF OF PANAMA THEN TURNS NW ALONG THE PACIFIC COAST OF NORTHWESTERN PANAMA...COSTA RICA AND NICARAGUA REACHING NEAR 13N88W...THEN TURNS SW THROUGH AN EMBEDDED 1010 MB LOW PRES AT 12N98W TO 09N112W WHERE LOW LEVEL WINDS INDICATE A TRANSITION TO AN ITCZ. THE ITCZ CONTINUES W THROUGH A 1012 MB EMBEDDED LOW PRES AT 09N123W...WITH ITCZ DIPPING FURTHER SW TO 06N128W BEFORE TURNING NW AND CONTINUING BEYOND 08N140W. ISOLATED MODERATE TO STRONG CONVECTION IS FLARING AROUND THE MONSOON TROUGH IN THE AREA FROM 07N TO 17N BETWEEN 86W AND 102W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED ALONG THE TROUGH WITHIN 90 NM EITHER SIDE OF A LINE FROM 07N109W TO 09N115W AND ANOTHER LINE FROM 08N117W TO 08N123W TO 06N128W. ...DISCUSSION... A LONGWAVE RIDGE DOMINATES THE EASTERN N PACIFIC AND THE WESTERN CONUS WITH AN UPPER ANTICYCLONE CENTERED AT 24N118W...RIDGING N BEYOND 32N116W TO A CREST OVER CENTRAL OREGON. AN UPPER RIDGE EXTENDS E TO A CREST AT 22N112W AND A RIDGE ALSO EXTENDS SW TO A SHARP CREST AT 10N140W. A SMALL MID LEVEL CYCLONE IS NOTED ALONG THE NORTHERN RIDGE NEAR 31N115W...WITH A MID LEVEL TROUGH EXTENDING S TO 28N116W. TROPICAL DEPRESSION LANE IS UNDER THE WESTERN PERIPHERY OF THE LARGE RIDGE WITH SOME OF ITS DEBRIS MOISTURE ADVECTED N UNDER THE RIDGE TO 31N123W. HOWEVER...A NARROW BAND OF THE TROPICAL CYCLONES MOISTURE HAS BEEN TAPPED BY THE MID LEVEL TROUGH...WITH A MOISTURE PLUME NOTED WITHIN 60 NM OF LINE FROM 27N120W TO OVER THE BAJA PENINSULA AT 28N...TO OVER SW ARIZONA WHERE IT CURRENTLY EVAPORATES. AN UPPER TROUGH CONTINUES NW OF THE DISCUSSION AREA...BUT STILL IS PROVIDING THE GRADIENT FOR A SOUTHWESTERLY 50 KT JET TO CONTINUE ALONG THE W PERIPHERY OF THE UPPER RIDGE...ROUGHLY WITHIN 90 NM OF LINE FROM 26N138W TO NEAR 33N129W. WEAK UPPER DIFFLUENCE S OF OF THE LARGE RIDGE IS SUPPORTING THE CONVECTION ALONG THE ITCZ PREVIOUSLY DESCRIBED. THE RESULTANT DEBRIS MOISTURE IS EVAPORATING NEAR THE CONVECTIVE CLUSTERS AS THE UPPER LEVELS ARE VERY DRY S OF 15N BETWEEN 110W AND 140W. A NARROW MOISTURE PLUME ORIGINATING FROM ITCZ CONVECTION W OF 140W...IS NOW SPREADING NE OVER THE DEEP TROPICAL PORTION FROM 13N140W TO 19N134W. A LONGWAVE TROUGH IS SHIFTING ACROSS EASTERN N AMERICA WITH AN EMBEDDED SHORTWAVE TROUGH EXTENDING FROM 31N97W ACROSS THE WESTERN GULF OF MEXICO TO BASE OVER THE BAY OF CAMPECHE. UPPER ANTICYCLONES ARE NOTED EITHER SIDE OF THIS UPPER TROUGH AT 19N107W AND 15N92W WITH THEIR ENVELOPE OF UPPER ANTICYCLONIC FLOW DOMINATING THE TROPICS BETWEEN 90W AND 112W. CONVECTION IS ENHANCED ALONG THE MONSOON TROUGH AS PREVIOUSLY MENTION...WITH THE DEBRIS MOISTURE TRAPPED FOR THE MOST PART WITHIN THE RIDGE. A BROAD INVERTED UPPER TROUGH HAS ITS MEAN AXIS S OF 21N ALONG 119W...AND IS SHIFTING W WITH TIME ERODING THE EASTERN PORTION OF THE TROPICAL RIDGE BETWEEN 120W AND 140W. EXCEPT FOR THE CONVECTION ALONG THE MONSOON TROUGH ITCZ TRANSITION AREA...THE UPPER TROUGH IS SUPPRESSING CONVECTION BETWEEN 110W AND 122W. AN UPPER CYCLONE OVER THE W CARIBBEAN NEAR THE CAYMAN ISLANDS HAS AN UPPER TROUGH EXTENDING S TO OVER CENTRAL PANAMA. THE UPPER LEVEL FLOW IS NORTHEASTERLY OVER THE DISCUSSION AREA E OF 93W AND SPREADING DEBRIS MOISTURE FORM FORMER CONVECTION ALONG THE MONSOON TROUGH SW TO ALONG 03N WHERE IT EVAPORATES. VERY DRY UPPER AIR IS INDICATED TO THE S OF 03N ACROSS THE ENTIRE DISCUSSION AREA EXTENDING NORTHWARD ACROSS THE EQUATOR FROM THE SOUTH PACIFIC WHICH APPEARS VERY DRY AS FAR S AS 13S TO THE E OF 140W. ELSEWHERE AT THE LOW LEVELS THE REMNANTS OF TROPICAL CYCLONE KRISTY ARE NEAR 25N118W AND ESTIMATED AT 1014 MB...AND ARE EXPECTED TO WEAKEN INTO AN OPEN TROUGH LATER TODAY AND DISSIPATE BY THU. GAP WINDS...BUILDING HIGH PRESSURE IN THE WAKE OF A FRONT THAT HAS STALLED DISSECTING THE GULF OF MEXICO FROM NE-SW...WILL SURGE AT 20 KT THROUGH THE ISTHMUS OF TEHUANTEPEC AND INTO THE GULF OF TEHUANTEPEC AROUND SUNRISE THIS MORNING. THESE DRAINAGE WINDS WILL INCREASE TO 20 TO 30 KT TONIGHT AND THEN PULSE THROUGH THE WEEKEND WITH THE STRONGEST WINDS OCCURRING LATE AT NIGHT TILL A FEW HOURS AFTER SUNRISE EACH DAY. $$ NELSON