000 AXNT20 KNHC 181740 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT THU OCT 18 2007 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN 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. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 44W S OF 16N MOVING W 10-15 KT. VISIBLE IMAGERY SHOWS A FAINT INVERTED V-SHAPE IN THE LOW-LEVEL CLOUD FIELD. BASED ON THIS PATTERN...THE WAVE HAS BEEN DRAWN SLIGHTLY LOWER AMPLITUDE THAN YESTERDAY. SCATTERED SHOWERS AND ISOLATED TSTMS ARE WITHIN 180 NM E AND 90 NM W OF THE AXIS. MORE ORGANIZED CLUSTERS OF TSTM ACTIVITY IS LOCATED FURTHER E AND W OF THE WAVE EMBEDDED IN THE ITCZ AND SUPPORTED BY DIFFLUENT FLOW ALOFT. WEAK TROPICAL WAVE IS IN THE E CENTRAL CARIBBEAN ALONG 67W S OF 17N MOVING W 10-15 KT. THIS WAVE HAS BEEN CHALLENGING TO TRACK OVER THE PAST COUPLE OF DAYS. A LONG-TERM SATELLITE LOOP AND SOUNDING DATA POSSIBLY SUGGESTS THAT THIS WAVE PASSED BARBADOS A DAY OR TWO AGO. THERE IS VERY LITTLE EVIDENCE OF THIS WAVE ON TODAY'S IMAGERY OR IN THE OTHER AVAILABLE DATA...SO MAINTAINED FORWARD CONTINUITY. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 10N14W 8N22W 8N36W 10N62W. SCATTERED MODERATE CONVECTION IS FROM 6N-11N BETWEEN 28W-38W AND FROM 10N-13N BETWEEN 49W-60W. DISCUSSION... GULF OF MEXICO... A LARGE STRONG LOW PRES SYSTEM OVER THE UPPER PLAINS HAS INDUCED DEEP LAYER TROUGHING OVER MEXICO AND THE W GULF. THIS SYSTEM HAS AN ASSOCIATED COLD FRONT BUT IS STILL INLAND OVER THE UNITED STATES. MODEL GUIDANCE SUGGESTS THAT THIS FRONT SHOULD ENTER THE NW WATERS LATER TONIGHT. SLY WINDS AHEAD OF THE FRONT ARE STRONGEST...NEAR 20 KT...IN THE N CENTRAL PORTION. UPPER DIFFLUENCE...BETWEEN SWLY FLOW AHEAD OF THE TROUGH AND AN UPPER HIGH OVER SE FLORIDA AND THE BAHAMAS...IS TRIGGERING SCATTERED SHOWERS AND TSTMS ACROSS THE GULF COAST N OF 29N BETWEEN 85W-90W AND WELL INLAND OVER GEORGIA...ALABAMA AND MISSISSIPPI. THE REMAINDER OF THE AREA HAS ONLY SCATTERED CLOUDINESS LIKELY SUPPRESSED BY STABLE MID AND UPPER LEVEL AIR...ESPECIALLY W OF 90W. LOOKING AHEAD...SOME MODELS SUGGEST THAT A STRONG COLD FRONT MAY MOVE INTO THE REGION EARLY NEXT WEEK WHICH COULD PROVIDE A SIGNIFICANT AIRMASS CHANGE. CARIBBEAN SEA... AN UPPER LOW IS TRACKING WWD ACROSS THE CARIBBEAN CENTERED ABOUT 150 NM E OF THE YUCATAN PENINSULA NEAR 19N85W. S TO SE FLOW ALOFT...BETWEEN THIS UPPER LOW AND A RIDGE EXTENDING FROM THE SRN GULF ACROSS THE BAHAMAS...IS DRAWING ABUNDANT TROPICAL MOISTURE FROM THE ITCZ BETWEEN 74W-81W. THIS MOISTURE PLUME HAS BEEN PERSISTENT AND SHIFTING W WITH THE UPPER LOW OVER THE PAST FEW DAYS. A 24-HOUR PRECIP REPORT FROM KINGSTON JAMAICA INDICATED THAT 2.41 INCHES HAS FALLEN. MORE RAIN IS OCCURRING AND EXPECTED TO CONTINUE THROUGHOUT THE DAY AS THE LATEST IR IMAGES AND LIGHTNING DATA SHOW A WELL DEFINED EXPANDING SWATH OF SHOWERS AND TSTMS MOVING NWD STEERED BY THE UPPER FLOW FROM 12N-18N BETWEEN 76W-79W. MUCH DRIER MID TO UPPER LEVEL AIR IS OVER THE LESSER ANTILLES AND THE CARIB WATERS E OF 70W ADVECTED BY N-NE UPPER FLOW AROUND THE AFOREMENTIONED RIDGE. THE WRN-MOST CARIB IS FAIRLY TRANQUIL WITH LITTLE SIGNIFICANT MOISTURE DIRECTLY UNDERNEATH THE UPPER LOW. ATLANTIC OCEAN... A LONG WAVE RIDGE/TROUGH/RIDGE PATTERN IS WELL ESTABLISHED ACROSS THE SUBTROPICAL ATLC. THE WRN ATLC RIDGE IS CENTERED OVER S FLA AND THE BAHAMAS WITH THE AXIS EXTENDING NWD ALONG 78W/79W. A VERY LARGE RATHER FLAT TROUGH LIES TO THE E OF THERE COVERING THE AREA BETWEEN 38W-65W N OF 20N. THIS TROUGH IS PROVIDING SUPPORT FOR A COLD FRONT WHICH ENTERS THE AREA NEAR 32N36W AND STRETCHES TO 27N45W AND IS THEN DISSIPATING ALONG 25N59W 27N67W. SCATTERED SHOWERS ARE GENERALLY WITHIN 120 NM OF THIS BOUNDARY. FARTHER W...AN AREA OF SCATTERED SHOWERS AND TSTMS IS OFF THE SE U.S. COAST FROM 29N-31N BETWEEN 77W-79W. THIS IS ASSOCIATED WITH A LOW-LEVEL TROUGH...WHICH WAS A CLOSED LOW-LEVEL CIRCULATION OFF THE COAST OF CENTRAL FLORIDA YESTERDAY. SIGNIFICANT DEVELOPMENT OF THIS SYSTEM IS NOT EXPECTED DUE TO UNFAVORABLE UPPER-LEVEL WINDS. THE SFC PATTERN IN THE CENTRAL AND E ATLC IS MOSTLY CONTROLLED BY RIDGING EXTENDING S/SW FROM A 1022 MB HIGH SITUATED NEAR 26N27W. THIS IS PRODUCING MAINLY LIGHT WINDS OVER THE SUBTROPICAL ATLC...WHILE MODERATE TRADES PERSIST IN THE TROPICS ESPECIALLY NEAR THE TROPICAL WAVES. THE UPPER PATTERN OVER THE E ATLC CONSISTS OF A LARGE SCALE RIDGE EXTENDING NWD FROM A HIGH CENTER NEAR 12N29W. THE STRONG CUT OFF LOW FROM A FEW DAYS AGO HAS OPENED INTO A TROUGH BUT IS STILL INTERRUPTING RIDGING SLIGHTLY FROM 28N34W TO 19N40W. CONVECTION IS MOSTLY CONFINED TO THE ITCZ SUPPORTED BY DIFFLUENCE ALOFT NEAR THE W PERIPHERY OF THE RIDGE AND JUST SE OF THE BASE OF THE TROUGH. FOR DETAILS SEE THE ITCZ SECTION. $$ CANGIALOSI