000 AXPZ20 KNHC 102130 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 2205 UTC WED SEP 10 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 2115 UTC. ...SPECIAL FEATURES... TROPICAL DEPRESSION LOWELL CENTERED NEAR 22.8N 111.9W OR ABOUT 90 NM W OF THE SOUTHERN TIP OF BAJA CALIFORNIA AT 10/2100 UTC IS MOVING NE OR 035 DEG AT 06 KT. ESTIMATED CENTRAL PRESSURE IS 1005 MB WITH MAXIMUM SUSTAINED WINDS ARE 30 KT WITH GUSTS TO 40 KT. AFTER PASSING N OF THE SUBTROPICAL RIDGE AXIS...LOWELL HAS BEGUN TO ENCOUNTER INCREASING MID-LATITUDE WESTERLY FLOW IN RESPONSE TO AN AMPLIFYING TROUGH OVER THE WESTERN CONUS. A COMPARISON OF LOWELL'S RECENT PROGRESS AND ITS FORECAST TRACK WITH A RECENT SNAPSHOT OF SEA SURFACE TEMPERATURES ACROSS THE REGION INDICATES THAT LOWELL IS RIDING CLOSE TO IF NOT JUST E OF THE 26.5C ISOTHERM. WITH STILL RELATIVELY WARM WATER ALONG ITS PATH AND CIMSS SHEAR ANALYSES INDICATING UNDER 10 KT OF S TO SW SHEAR...SEVERAL BURSTS OF DISORGANIZED CONVECTION CONTINUE TO DEVELOP WITHIN ABOUT 120 NM OVER THE NORTHERN SEMICIRCLE. HOWEVER... WEAKENING IS FORECAST AS LOWELL TAKES A GENERALLY NE PATH THROUGH SOUTHERN BAJA CALIFORNIA TONIGHT AND INTO THE SOUTHERN GULF OF CALIFORNIA THU MORNING BEFORE FINALLY DISSIPATING OVER NW MAINLAND MEXICO ON LATE THU OR EARLY FRI. MID- TO UPPER-LEVEL MOISTURE ASSOCIATED WITH THE REMAINS OF LOWELL IS EXPECTED TO SPREAD INTO THE DESERT SW AND SOUTHERN ROCKIES FRI AND SAT IN ADVANCE OF THE SAME AMPLIFYING MID- TO UPPER-LEVEL TROUGH MENTIONED ABOVE. PLEASE REFER TO THE LATEST NHC PUBLIC ADVISORY UNDER AWIPS HEADER MIATCPEP3 OR WMO HEADER WTPZ33 KNHC AND THE FULL FORECAST ADVISORY UNDER AWIPS HEADER MIATCMEP3 OR WMO HEADER WTPZ23 KNHC FOR MORE DETAILS. ...ITCZ... ITCZ AXIS LIES 09N85W TO 06N96W TO 07N110W...THEN RESUMES FROM T.D. LOWELL TO 16N116W TO 11N128W TO 06N140W. ISOLATED WEAK CONVECTION WITHIN 60 NM N OF AXIS BETWEEN 129W AND 130W. SCATTERED MODERATE CONVECTION WITHIN 270 NM SW OF MANZANILLO MX. SCATTERED MODERATE WITHIN 60 NM S OF AXIS FROM 06N87W TO 05N94W. ...DISCUSSION... THE WESTERN END OF THE ITCZ OVER THE TROPICAL EAST PACIFIC EXTENDS SOUTHWEST FROM TROPICAL DEPRESSION LOWELL TO AROUND 12N128.5W AND FINALLY TO 06N140W. SATELLITE PICTURES INDICATE THAT A WEAK LOW-LEVEL CYCLONIC CIRCULATION HAS FORMED WITHIN THE ITCZ IN THE VICINITY OF 12N128.5W AND IS DRIFTING SLOWLY NORTHWEST. AFTER A BURST OF DEEP CONVECTION EARLIER THIS MORNING...THE LOW-LEVEL CENTER HAS BECOME COMPLETELY EXPOSED AS NE TO E SHEAR BEGINS TO TAKE A TOLL. IN FACT...CIMSS SHEAR ANALYSES REVEAL MORE THAN 20 KT OF NE TO SHEAR OVER THE SYSTEM...WHICH SHOULD PROVE TO BE A STRONG INHIBITING FACTOR FOR ANY FUTURE DEVELOPMENT. PERHAPS THIS IS A REASON WHY NO GLOBAL MODEL IS FORECASTING DEVELOPMENT FROM THIS AREA OVER THE NEXT FEW DAYS. TO THE E...AN ANOMALOUS LOW-LEVEL WESTERLY FLOW REMAINS IN PLACE MOSTLY S OF 20N E OF 120W...AS HAS BEEN THE CASE FOR MOST OF THE LAST WEEK OF AUGUST AND NOW THE FIRST 10 DAYS OF SEPTEMBER. THIS PATTERN SUPPORTS A MONSOON TROUGH-TYPE FEATURE...DISPLACED N OF ITS CLIMATOLOGICAL POSITION...FROM CENTRAL AMERICA NORTHWEST THROUGH MUCH OF SOUTHERN MEXICO TO NEAR TROPICAL DEPRESSION LOWELL. CYCLONIC SHEAR AND SPEED CONVERGENCE ALONG THE TROUGH AXIS HELPED SPAWN SCATTERED TO LOCALLY NUMEROUS TSTMS WITHIN ABOUT 330 NM OF THE SW COAST OF MEXICO NEAR MANZANILLO THIS MORNING. SINCE THEN...MUCH OF THE CONVECTION HAS WEAKENED CONSIDERABLY WITH LITTLE MORE THAN CIRRUS LINGERING IN ITS WAKE. MODELS SHOW LITTLE CHANGE TO THE WESTERLY LOW-LEVEL EXCEPT TO CURB IT TO THE WEST AND HIGH PRESSURE OVER THE NE PACIFIC BUILDS INTO THE REGION BETWEEN 110-120W BY EARLY THIS WEEKEND. ELSEWHERE...LONG PERIOD SOUTHWEST SWELL ARRIVING FROM THE SOUTHERN HEMISPHERE CONTINUES TO ENGULF MUCH OF THE TROPICAL EAST PACIFIC WATERS...EXCEPT OVER THE W OF 120W WHERE SOUTHEAST SWELL PREVAILS. MODEL GUIDANCE ALREADY SHOWS WAVE HEIGHTS HAVE ALREADY PEAKED AROUND 7 TO 9 FT OVER THIS ENTIRE REGION EARLIER TODAY BUT ARE FORECAST TO SUBSIDE TO 5 TO 8 FT BY FRI. $$ KIMBERLAIN