000 AXNT20 KNHC 161804 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT THU APR 16 2009 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER OBSERVATIONS...AND RADAR. BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1745 UTC. ...THE ITCZ... THE ATLC ITCZ EXTENDS FROM THE AFRICAN COAST AT 04N07W TO THE EQUATOR AT 21W THEN CONTINUES S OF THE EQUATOR TO NE BRAZIL NEAR 03S42W. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE OBSERVED WITHIN 90 NM OF THE ITCZ AXIS BETWEEN 07W AND 13W...WITHIN 90 NM NORTH AND WITHIN 240 NM SOUTH OF THE ITCZ BETWEEN 19W AND 29W...AND FROM 04S TO 01N BETWEEN 34W AND 48W. ...DISCUSSION... THE GULF OF MEXICO... AN UPPER LEVEL ANTICYCLONE S OF THE AREA RIDGES N ACROSS THE CENTRAL GULF OF MEXICO. UPPER MOISTURE IS MOVING ANTICYCLONICALLY E ACROSS THE RIDGE N OF A LINE FROM 24N95W TO 29N84W...WHILE DRY UPPER AIR IS NOTED S OF THE SAME LINE. AT THE LOW LEVELS A FRONTAL TROUGH EXTENDS FROM THE FLORIDA STRAITS TO THE CENTRAL GULF OF MEXICO THEN S TO THE MEXICAN COAST NEAR 22N98W. HIGH PRES CENTERS HAVE FORMED ALONG THE ATLC RIDGE OVER CUBA WITH A LOW LEVEL RIDGE AMPLIFYING NW AND EFFECTIVELY PUSHING THE FRONTAL REMNANTS N OVER THE CENTRAL GULF. ASSOCIATED CONVECTION IS SHALLOW DUE TO THE DRY UPPER AIR ALOFT AND THE SW SHEAR IN THE UPPER ANTICYCLONIC FLOW. THE CARIBBEAN SEA... AN UPPER TROUGH EXTENDS S OVER THE NW CARIBBEAN TO NEAR JAMAICA AND IS PROGRESSING E WITH TIME. AN UPPER ANTICYCLONE OVER S AMERICA NEAR 08N60W RIDGES NW OVER THE CENTRAL CARIBBEAN CRESTING ALONG POINTS 11N82W TO 15N75W TO BEYOND 18N62W. ALTHOUGH UPPER LEVEL THIN CIRRIFORM CLOUDS ARE STREAMING NE ACROSS THE UPPER RIDGE E OF 80W...THE UPPER LEVELS ARE FOR THE MOST PART QUITE DRY. AT THE LOW LEVELS LOCALLY BROKEN TRADE WIND CUMULUS IS RACING W ACROSS THE CARIBBEAN EXCEPT OVER THE AREA BETWEEN GRAND CAYMAN AND CUBA WHERE THE SKIES ARE MOSTLY CLEAR. HEAVY SHOWERS ARE NOTED OVER SOUTHERN HAITI AND S OF THE VIRGIN ISLANDS NEAR 17N64W. THE ATLANTIC OCEAN... AN UPPER LEVEL TROUGH IS SWINGING THROUGH THE SUBTROPICAL ATLC WITH MEAN AXIS ALONG 32N73W TO 21N76W. AN ASSOCIATED SURFACE FRONT LIES ALONG 32N65W TO THE NW BAHAMAS WHERE THE FRONT BECOMES NEARLY STATIONARY THROUGH THE STRAITS OF FLORIDA. UPPER DIFFLUENCE E OF THE UPPER TROUGH IS ENHANCING CONVECTION ALONG THE FRONT WITH LIGHTNING DATA CURRENTLY REPORTING NUMEROUS HITS WITHIN 15 NM OF LINE 20N85W TO 24.5N74W. ANOTHER UPPER TROUGH DOMINATES THE CENTRAL SUBTROPICAL ATLC ROUGHLY FROM 32N20W TO 20N32W TO 15N45W WITH DRY UPPER AIR ROUGHLY WITHIN 180 NM EITHER SIDE OF THE TROUGH. A SURFACE FRONTAL TROUGH LIES ALONG 32N28W TO 25N53W ACCOMPANIED BY A THIN LINE OF SHOWERS. UPPER RIDGING IS NOTED BETWEEN 65W AND THIS TROUGH...AND ALSO SE OF THE TROUGH TO INCLUDE MOST OF TROPICAL AFRICA. $$ NELSON