000 AXNT20 KNHC 210428 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 AM EDT THU SEP 21 2006 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHEASTERN SECTIONS OF SOUTH AMERICA...AND THE ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR... AND METEOROLOGICAL ANALYSIS. BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0315 UTC. ...SPECIAL FEATURES... HURRICANE HELENE IS CENTERED NEAR 27.1N 57.0W OR ABOUT 513 MILES SOUTHEAST OF BERMUDA AT 21/0300 UTC MOVING NORTH AT 8 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 961 MB. MAXIMUM SUSTAINED WIND SPEED IS 85 KT WITH GUSTS TO 105 KT. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS. SCATTERED MODERATE/ISOLATED STRONG CONVECTION COVERS THE AREA FROM 26N-29N BETWEEN 55W-58W. DENSE OVERCAST CLOUDS COVERS A MUCH LARGER AREA FROM 24N-32N BETWEEN 53W-61W. ...TROPICAL WAVES... TROPICAL WAVE IS W OF THE CAPE VERDE ISLANDS ALONG 31W S OF 19N MOVING W 15-20 KT. BROAD MID LEVEL INVERTED-V CURVATURE WITH SCATTERED MODERATE/STRONG CONVECTION W OF THE WAVE AXIS WITHIN 90/120 NM OF LINE 18N31W-11N35W. TROPICAL WAVE IS ALONG 47W S OF 18N MOVING W 15 KT. WEAK LOWER AMPLITUDE INVERTED-V SIGNATURE WITH CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION MOSTLY E OF THE WAVE AXIS FROM 12N-16N BETWEEN 41W-48W. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 10N14W 12N22W 11N30W 12N41W 8N51W ACROSS N PORTION OF SOUTH AMERICA AND PANAMA INTO THE E PACIFIC REGION NEAR 9N83W. SCATTERED MODERATE/STRONG CONVECTION IS MOVING OFF THE COAST OF AFRICA FROM 9N-14N E OF 18W. SCATTERED CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION ARE FROM 5N-16N BETWEEN 19W-35W. ...DISCUSSION... GULF OF MEXICO... BROAD UPPER RIDGE ANCHORED ALONG THE W COAST OF MEXICO COVERS ALL OF MEXICO WITH A RIDGE AXIS EXTENDING NE OVER THE MISSISSIPPI VALLEY AND A SECOND RIDGE AXIS EXTENDING E OVER THE GULF ALONG 24N TO 85W. DEEP LAYER TROUGH OVER THE FAR E US AND THE W ATLC EXTENDS S OVER THE E GULF N OF 24N E OF 85W WITH THE ASSOCIATED COLD FRONT ENTERING THE GULF OVER S FLORIDA NEAR 26N81W TO 26N86W WHERE IT BECOMES STATIONARY FRONT ACROSS THE REMAINDER OF THE GULF. ISOLATED SHOWERS ARE FROM 24N-27N E OF 88W TO THE FLORIDA COAST AND OVER THE FLORIDA KEYS. DIFFLUENCE OVER THE BAY OF CAMPECHE IS GENERATING SCATTERED SHOWERS/ THUNDERSTORMS S OF 20N E OF 96W TO INLAND OVER S MEXICO. CARIBBEAN SEA... BROAD UPPER RIDGE THAT COVERS THE W GULF OF MEXICO ALSO COVERS THE NW CARIBBEAN W OF 85W. AN UPPER LOW IS IN THE W CARIBBEAN NEAR 17N82W WITH A TROUGH EXTENDING TO OVER CENTRAL CUBA NEAR 22N79W AND SW TO THE TIP OF HONDURAS/NICARAGUA. THIS IS GENERATING SCATTERED SHOWERS/THUNDERSTORMS OFF THE COAST OF NICARAGUA FROM 12N-16N BETWEEN 78W-83W. UPPER HIGH COVERS THE REMAINDER OF THE CARIBBEAN ANCHORED JUST S OF HAITI NEAR 17N74W THUS LEAVING THE CARIBBEAN E OF 77W DRY TONIGHT. ATLANTIC OCEAN... BROAD UPPER TROUGH OVER THE FAR E US AND THE GULF OF MEXICO COVERS THE W ATLC N OF 26N W OF 75W WITH THE ASSOCIATED COLD FRONT ENTERING THE AREA NEAR 32N71W SW ACROSS FLORIDA INTO THE GULF OF MEXICO NEAR 26N81W. ISOLATED SHOWERS ARE WITHIN 90 NM OF LINE FROM THE FLORIDA E COAST NEAR 26N80W TO BEYOND 32N69W. AN UPPER RIDGE IS ANCHORED CLOSE TO THE BAHAMAS NEAR 24N75W EXTENDING A RIDGE AXIS NE TO BEYOND 32N68W. NARROWING UPPER TROUGH IS WEDGE BETWEEN THE ABOVE RIDGE AND THE UPPER HIGH ASSOCIATED WITH HURRICANE HELENE WHICH HAS BROADEN OVER THE PAST 24 HOURS TO ENCOMPASS A LARGE AREA FROM 21N-40N BETWEEN 48W-63W. NARROWING CUT-OFF UPPER LOW E OF HELENE IS BEING COMPRESSED BY THE UPPER HIGH OFF THE COAST OF AFRICA AND IS CENTERED NEAR 22N38W EXTENDING A TROUGH AXIS NE/SW FROM 27N34W-18N43W. UPPER HIGH ANCHORED NE THE CAPE VERDE ISLANDS NEAR 18N23W COVERS THE REMAINDER OF THE E ATLC. AT THE SURFACE...A 1022 MB HIGH IS LOCATED NEAR 29N38W WITH A RIDGE EXTENDING S TO 20N FROM AFRICA TO 50W WITH THIS AREA VERY DRY TONIGHT. $$ WALLACE