000 AXNT20 KNHC 181804 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 105 PM EST MON DEC 18 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... METEOROLOGICAL ANALYSIS...WEATHER OBSERVATIONS...AND RADAR. BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...THE ITCZ... 7N9W 5N16W 5N30W 4N40W 2N50W INTO NORTHEASTERN BRAZIL NEAR 2N52W. WIDELY SCATTERED MODERATE SHOWERS TO ISOLATED STRONG THUNDERSTORMS ARE FROM 4N TO 8N BETWEEN 33W AND 45W...AND FROM 7N TO 9N BETWEEN 53W AND 56W. ISOLATED MODERATE SHOWERS ARE ELSEWHERE FROM THE EQUATOR TO 4N BETWEEN 10W AND 30W... AND FROM THE EQUATOR TO 10N BETWEEN 30W AND 50W. ...DISCUSSION... THE GULF OF MEXICO AND THE ATLANTIC OCEAN NORTH OF 20N WEST OF 60W... AN UPPER LEVEL SHORTWAVE TROUGH HAS BEEN MOVING STEADILY NORTHEASTWARD...AND NOW EXTENDS FROM A SMALL CYCLONIC CIRCULATION CENTER IN NORTHEASTERN TEXAS TO THE LOWER RIO GRANDE VALLEY OF TEXAS AND EXTREME NORTHEASTERN MEXICO. THIS FEATURE IS SURROUNDED BY DRY AIR...AND THUS NO DEEP CONVECTIVE PRECIPITATION IS IN THE AREA. BROKEN TO OVERCAST LOW TO MIDDLE LEVEL CLOUDS IN INDIVIDUAL CLUSTERS ARE WITHIN 30 TO 60 NM ON EITHER SIDE OF 23N84W JUST OFF THE NORTHWESTERN CUBA COAST...TO 25N88W 26N91W TO 29N95W ALONG THE TEXAS COAST. A WEST-TO-EAST SURFACE RIDGE RUNS FROM MISSISSIPPI TO SOUTH CAROLINA INTO THE ATLANTIC OCEAN TO A 1030 MB HIGH PRESSURE CENTER NEAR 33N67W. AN UPPER LEVEL RIDGE EXTENDS THROUGH SOUTHERN LOUISIANA INTO THE GULF OF MEXICO NEAR 26N92W TO CAMPECHE MEXICO. AN ATLANTIC MIDDLE TO UPPER LEVEL CYCLONIC CIRCULATION CENTER NEAR 26N76W IS SENDING DRY AIR CYCLONIC FLOW ACROSS FLORIDA FROM 28N INTO THE NORTHWESTERN CARIBBEAN SEA. THE COMPARATIVELY DRIEST AIR EXISTS FROM THE BAHAMAS TO THE EASTERN GULF OF MEXICO NORTH OF 20N BETWEEN 75W AND 88W. BROAD AND GENTLE ANTICYCLONIC FLOW IS WITH AN UPPER LEVEL RIDGE ALONG 15N66W 24N67W. THE CARIBBEAN SEA... A MIDDLE TO UPPER LEVEL TROUGH ENTERS THE AREA FROM AN ATLANTIC OCEAN CYCLONIC CIRCULATION CENTER NEAR 26N76W...TO THE COAST OF CUBA NEAR 23N80W...INTO THE NORTHWESTERN CORNER OF THE AREA... AND EVENTUALLY TO THE WATERS JUST EAST OF EASTERN HONDURAS NEAR 15N82W. BROAD AND GENTLE ANTICYCLONIC FLOW IS WITH AN UPPER LEVEL RIDGE ALONG 15N66W 24N67W. LOW TO MIDDLE LEVEL CYCLONIC FLOW COVERS THE SOUTH CENTRAL AND SOUTHWESTERN SECTIONS... IN MIDDLE TO UPPER LEVEL DRY AIR...SOUTH OF 17N71W 15N78W 14N83W. UPPER LEVEL SOUTHERLY FLOW MOVES FROM COLOMBIA AND VENEZUELA INTO THE SOUTHERN CARIBBEAN SEA WATERS...AND EVENTUALLY TURNS ANTICYCLONICALLY INTO THE ATLANTIC OCEAN EAST OF THE SOUTHEASTERN CORNER OF THE AREA. THE ATLANTIC OCEAN... A CENTRAL ATLANTIC DEEP LAYER TROUGH PASSES THROUGH 32N42W TO 26N43W TO 18N50W. THIS TROUGH SUPPORTS THE COLD FRONT THROUGH 32N42W TO A 1015 MB LOW PRESSURE CENTER NEAR 27N47W...TO ANOTHER 1015 MB LOW CENTER NEAR 24N58W. A SURFACE TROUGH CONTINUES FROM 24N58W TO 22N74W. WIDELY SCATTERED TO SCATTERED MODERATE SHOWERS/ ISOLATED STRONG THUNDERSTORMS FROM SOUTHEASTERN CUBA NEAR 20N TO 25N BETWEEN 64W AND 77W. THIS PRECIPITATION IS CLOSE TO THE 26N76W MIDDLE TO UPPER LEVEL CYCLONIC CENTER AND THE 24N58W 22N74W SURFACE TROUGH. THE MIDDLE TO UPPER LEVEL TROUGH WHICH COVERED THE EASTERN ATLANTIC OCEAN DURING THE LAST FEW DAYS HAS FALLEN APART AND WHATEVER REMAINS OF IT IS NOT ORGANIZED OR AS IMPRESSIVE-LOOKING AS IT HAD BEEN A FEW DAYS AGO. A SURFACE TROUGH STARTS OUT AT A 1004 MB GALE CENTER NEAR 37N32W...AND PASSES THROUGH 32N22W TO 25N23W TO 19N30W 13N40W 9N51W. THE TROUGH IS WHAT REMAINS FROM THE EASTERN ATLANTIC OCEAN COLD FRONT FROM THE LAST FEW DAYS. $$ MT