000 AXPZ20 KNHC 241600 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 1605 UTC THU SEP 24 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 1500 UTC. ...SPECIAL FEATURE... TROPICAL STORM NORA WAS CENTERED NEAR 17.3N 120.0W AT 24/1500 UTC MOVING WNW OR 290 DEG AT 4 KT. ESTIMATED MINIMUM CENTRAL PRESSURE WAS 1000 MB. MAXIMUM SUSTAINED WIND SPEED REMAINED AT 45 KT WITH GUSTS TO 55 KT. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP2/WTPZ22 KNHC FOR MORE DETAILS. NUMEROUS MODERATE TO STRONG CONVECTION COULD BE FOUND WITHIN 70 NM NW AND 50 NM SW SEMICIRCLES...WITH SCATTERED MODERATE CONVECTION WITHIN 110 NM NE AND 80 SW SEMICIRCLES. NORA HAS LIKELY ALREADY REACHED ITS PEAK INTENSITY AND IS EXPECTED TO BEGIN A GRADUAL WEAKENING TREND SHORTLY...AND THEN MORE RAPIDLY BY 24-36 HOURS. A WEST TO WEST-NORTHWEST TRACK OVER THE NEXT FEW DAYS WILL MOVE THE CYCLONE INTO INCREASINGLY STRONGER UPPER LEVEL WIND SHEAR ASSOCIATED WITH AN UPPER TROUGH CURRENTLY LOCATED TO THE W AND NW OF NORA...WHICH WILL ACT TO PRODUCE INCREASINGLY DETRIMENTAL SHEAR ACROSS THE SYSTEM. NORA IS FORECAST TO WEAKEN TO A TROPICAL DEPRESSION BY 36 HOURS AND THEN TO A REMNANT LOW BY 72 HOURS. ...THE ITCZ... THE INTERTROPICAL CONVERGENCE ZONE WAS ALONG 08N78W TO 10N100W TO 14N115W. THE AXIS CONTINUES AGAIN FROM 13N122W TO 09N136W. SCATTERED MODERATE TO ISOLATED STRONG WITHIN 210 NM N OF AXIS BETWEEN 87W TO 105W. NUMEROUS MODERATE TO SCATTERED STRONG WITHIN 180 NM N OF AXIS BETWEEN 128W TO 137W. ...DISCUSSION... W OF 120W... A 1007 MB LOW PRES SYSTEM EMBEDDED IN THE ITCZ WAS NEAR 09.5N136W MOVING W AT 7 KT. NUMEROUS MODERATE TO STRONG CONVECTION HAS IGNITED FROM 10.5N TO 14N BETWEEN 129W AND 139W ASSOCIATED WITH THE BROADER CIRCULATION OF THIS LOW. AN OVERNIGHT QUIKSCAT PASS SUGGESTED SOUTHERLY INFLOW INTO THE SYSTEM WAS IN THE 20 TO 30 KT RANGE...WHILE A BROAD AREA OF 20 TO 25 KT WINDS WERE OCCURRING AT THAT TIME IN THE NE QUADRANT. ANTICYCLONIC UPPER LOW FLOW ACROSS THIS AREA IS BEING MAINTAINED BY A SYNOPTIC SCALE UPPER LOW AND TROUGH ACROSS THE HAWAIIAN ISLANDS REGION...AND SHOULD HELP TO MAINTAIN ACTIVE CONVECTION BETWEEN 130W AND 140W DURING THE NEXT 24 HOURS. HIGH PRESSURE WELL TO THE N OF THIS LOW IS EXPECTED TO MAINTAIN A BROAD ZONE OF 20 KT WINDS N THROUGH NW OF THIS SYSTEM...AND N OF 15N WITH SEAS IN THE 9-10 FT RANGE THROUGH FRIDAY. OVER NORTH WATERS...SHORTWAVE ENERGY ALOFT LEFT BEHIND BY BOTH THE POSITIVELY TILTED UPPER TROUGH OVER THE CENTRAL U.S. AND NW MEXICO AND THE WEAKENING DEEP-LAYER TROUGH ALONG 133W N OF 32N WILL JOIN TOGETHER TO FORM AND UPPER LOW OVER N WATERS OVER THE NEXT TWO DAYS. THIS WILL PREVENT THE SURFACE RIDGE OVER THE N WATERS FROM INTENSIFYING APPRECIABLY. IT WILL ALSO DISRUPT THE STRONG SUBSIDENCE N OF 24N E OF 135W WILL BREAK UP SOME OF THE DENSE STRATOCUMULUS FOUND THERE CURRENTLY. THE SURFACE RIDGE AXIS DESCRIBED ABOVE WILL SHIFT EASTWARD OVER THE NEXT TWO DAYS AND EASTERLY WINDS INDUCED BY THE MERIDIONAL PRES GRADIENT WILL INCREASE TO 20 KT OVER NW WATERS BY FRI MORNING. THIS AREA ALSO WILL SEE THE ARRIVAL OF 15-16 SECOND PERIOD NW SWELL LATE FRI. E OF 120W... THE WEAKENING COLD FRONT ASSOCIATED WITH A POSITIVELY TILTED TROUGH ALOFT OVER THE CENTRAL U.S. AND NW MEXICO BROUGHT 20 KT WINDS TO THE GULF OF CALIFORNIA N OF 27N YESTERDAY EVENING...AND HAVE SINCE DIMINISHED TO 15-20 KT THIS MORNING AS INDICATED BY A 13Z QUIKSCAT PASS. THIS FRONT HAS ALSO BROUGHT NORTHERLY FLOW IN THE 20-25 KT RANGE INTO THE GULF OF TEHUANTEPEC ACCORDING TO THE 0012 UTC QUIKSCAT PASS. WINDS HERE ARE EXPECTED TO DIMINISH BELOW 20 KT FRI NIGHT AS THE HIGH PRES BEHIND THE COLD FRONT ERODES...WEAKENING THE PRES GRADIENT. THE 50 KT SW TO WLY UPPER JET MEANDERING FROM 21N128W TO 32N101W WILL MOVE LITTLE AND CONTINUE TO INHIBIT CONVECTION ACROSS NW MEXICO THE NEXT FEW DAYS. SCATTERED MODERATE ISOLATED CONVECTION CURRENTLY LIES E OF 110W TO THE MEXICAN COAST FROM 19N TO 21N IN THE DIFFLUENT AREA ALONG THE UPPER RIDGE AXIS EXTENDING FROM AN ANTICYCLONE OVER THE GULF OF MEXICO NEAR 22N102W SOUTHWESTWARD TO 17N112W. ELSEWHERE...BROADLY DIFFLUENT FLOW BETWEEN THIS RIDGE AXIS AND A WEAK UPPER LOW CENTERED SE OF THE GALAPAGOS ISLANDS IS SUPPORTING SCATTERED TO NUMEROUS THUNDERSTORMS NEAR THE ITCZ FROM 105W E INTO CENTRAL AMERICA AND THE FAR W CARIB. A VERY BROAD LOW TO MID LEVEL CYCLONIC/MONSOON CIRCULATION HAS BECOME WELL ESTABLISHED S OF 20N AND BETWEEN 70W AND 110W AND SHOULD CONTINUE TO FUEL THIS AREA WITH AMPLE MOISTURE FOR ACTIVE THUNDERSTORM ACTIVITY DURING THE NEXT 24 HOURS...WITH THE STRONGEST ACTIVITY GRADUALLY SHIFTING W OF 105W DURING THE DAY SATURDAY. $$ STRIPLING