000 AXPZ20 KNHC 221620 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 1605 UTC SAT SEP 22 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1515 UTC. ...SPECIAL FEATURES... THE TROPICAL DEPRESSION ACROSS THE EASTERN PACIFIC HAS BEEN UPGRADED THIS MORNING TO TROPICAL STORM MIRIAM...LOCATED NEAR 3.9N 107.7W 1003 MB AT 1500 UTC SEP 22 MOVING WNW OR 285 DEG AT 4 KT. MAXIMUM SUSTAINED WINDS 35 KT GUSTS 45 KT. THIRTEEN-E CENTERED NEAR 13.7N 107.5W AT 22/0900 UTC MOVING W OR 280 DEGREE AT 6 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1003 MB. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP3/WTPZ23 KNHC FOR MORE DETAILS. MIRIAM HAS SEVERED AWAY FROM THE MONSOON TROUGH...AND CONVECTIVE BANDING HAS IMPROVED WITHIN THE BROADER CIRCULATION OF MIRIAM IN RECENT HOURS...WITH AN ELONGATED BAND SOME 90-150 NM FROM THE CENTER ACROSS THE SW QUADRANT...AND ISOLATED DEEP CELLS PULSING WITHIN 90 NM OF THE ESTIMATED CENTER ACROSS THE NE SEMICIRCLE. OTHERWISE...SCATTERED MODERATE TO STRONG CONVECTION WAS NOTED WITHIN 210 NM NE AND 180 NM SW SEMICIRCLES OF CENTER. MIRIAM IS EXPECTED TO CONTINUE MOVING NW FOR THE NEXT 48 HOURS...IN A REGION OF FAVORABLE ATMOSPHERIC AND OCEANIC CONDITIONS...AND IS FORECAST TO GRADUALLY STRENGTHEN AND BECOME A HURRICANE WITHIN 36 HOURS. BASED ON THE CURRENT MODEL GUIDANCE...THIS SYSTEM IS NOT EXPECTED TO BE A THREAT TO LAND. ...TROPICAL WAVES... SCATTERED MODERATE TO STRONG CONVECTION SHIFTING WWD ACROSS THE TROPICAL EPAC APPEARS TO BE IN SYNC WITH A TROPICAL WAVE ACROSS THE YUCATAN PENINSULA...AND IS ASSUMED TO BE THE SOUTHERN PORTION OF THIS WAVE....CENTERED ALONG ABOUT 90W...AND MOVING W 10-15 KT. THE WAVE HAS PERTURBED THE MONSOON TROUGH AND A WAVE OR UNDULATION IN THE TROUGH WAS EVIDENT IN OVERNIGHT SCATTEROMETER PASSES. THIS SOUTHERN PORTION OF THE WAVE WILL BREAK AWAY FROM THE REST OF THE WAVE ACROSS CENTRAL AMERICA IN THE NEXT 24 HOURS...AND CONTINUE TO SHIFT WWD. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... MONSOON TROUGH EXTENDS FROM COLOMBIA NEAR 10N73W ACROSS THE EXTREME SW CARIBBEAN AND COSTA RICA TO NEAR 10N90W TO 08N96W TO 12N100W...WHERE IT HAS SEVERED...THEN RESUMES W OF T.S. MIRIAM FROM 14N114W TO 14N120W TO 09N127W...WHERE IT TRANSITIONS TO ITCZ...CONTINUING ON TO BEYOND 08N140W. SCATTERED MODERATE ISOLATED STRONG WITHIN 210 NM S AND 360 NM N OF TROUGH AXIS BETWEEN 84W AND 100W. SCATTERED MODERATE ISOLATED STRONG WITHIN 90 NM N AND 210 NM S OF ITCZ AXIS. ...DISCUSSION... ALOFT...AN UPPER TROUGH EXTENDS ACROSS NW PORTIONS OF THE AREA FROM THEN CENTRAL CALIFORNIA COAST TO A CUT OFF LOW NEAR 24N145W...WITH SWLY WINDS OF 40-60 KT TRANSPORTING ABUNDANT MID TO UPPER LEVEL MOISTURE ACROSS THE NW CORNER OF THE AREA. A NARROW RIDGE WAS LOCATED IMMEDIATELY TO THE SE OF THIS TROUGH...FROM AN ANTICYCLONE OVER THE ITCZ NEAR 09N150W TO NE PORTIONS OF THE AREA NEAR 29N117W. A BROAD AND PERSISTENT UPPER TROUGH CONTINUES ACROSS THE NRN GULF OF MEXICO AND THE N HALF OF OLD MEXICO...WITH BROAD RIDGING GENERALLY PREVAILING TO ITS S...EXTENDING E TO W BETWEEN 80W AND 120W. THIS FLOW CONTINUES TO YIELD A LOW SHEAR AND DIVERGENT ENVIRONMENT...AND WILL REMAIN FAVORABLE FOR DEEP CONVECTION ACROSS THIS REGION THROUGH SUN. A MID LEVEL TUTT AXIS CAN BE SEEN SEPARATING THE TWO RIDGES... FROM THE S END OF BAJA CALIFORNIA TO A WWD DRIFTING TUTT LOW NEAR 14N128W. AT LOW LEVELS...A 1024 MB HIGH PRES CENTERED N OF AREA NEAR 34N136W EXTENDS A RIDGE ACROSS THE N WATERS TO NEAR 24N115W. AN AREA OF FRESH TRADE WINDS IS SEEN ON THE SOUTHERN PERIPHERY OF THE RIDGE FROM 10N TO 20N W OF 133W...AND WAS CONFIRMED OVERNIGHT BY PARTIAL SCATTEROMETER PASSES. TRADES WILL DIMINISH TO 20 KT OR LESS IN ABOUT 24 HOURS AS HIGH PRES SLIGHTLY WEAKENS AND A COLD FRONT APPROACHES AND THEN STALLS TO THE NW. HOWEVER...NW SWELL GENERATED BEHIND THE FRONT WILL IMPACT THE NW WATERS SUN AND MON...BUILDING SEAS TO AROUND 11 FT ACROSS FAR NW PORTIONS. GAP WINDS...A NORTH TO SOUTH ALIGNED TROUGH ACROSS THE BAY OF CAMPECHE HAS COMBINED WITH A MODEST HIGH PRES RIDGE ACROSS EASTERN MEXICO AND THE W GULF OF MEXICO TO SUPPORT NLY GAP WINDS THROUGH THE GULF OF TEHUANTEPEC. COMPUTER MODELS SUGGEST N TO NE WINDS 20-25 KT TO CONTINUE THROUGH AND DOWNWIND OF THE GULF DURING THE NEXT 48 HOURS...WITH SEAS BUILDING TO 9 FT LATE TONIGHT. $$ STRIPLING