000
AXNT20 KNHC 240001
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU OCT 23 2008

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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...TROPICAL WAVES...
THE 59TH TROPICAL WAVE OF THIS SEASON HAS EMERGED OFF THE WEST
COAST OF AFRICA TODAY AND IS ANALYZED ON THE 1800 UTC MAP ALONG
16W SOUTH OF 15N. THE WAVE SHOWS UP ON THE TPW PRODUCT FROM
CIMSS WITH A SURGE OF MOISTURE BETWEEN THE WAVE AXIS AND THE
AFRICAN COAST. THE HOVMOLLER DIAGRAM ALSO DEPICTS THE WWD
PROPAGATION OF THE WAVE SINCE YESTERDAY. INITIAL MOTION
ESTIMATES MOVE THE WAVE WWD AT 10-15 KT. SCATTERED MODERATE TO
ISOLATED STRONG CONVECTION IS FROM 5N-9N BETWEEN 16W-19W.
CLUSTERS OF MODERATE CONVECTION ARE BEHIND THE WAVE AXIS NEAR
9N13W AND 6N14W.

A TROPICAL WAVE IS ALONG 30W S OF 14N MOVING W NEAR 10 KT. DEEP
LAYER DRY AIR IS GENERALLY SUPPRESSING CONVECTION NEAR THE WAVE.
HOWEVER...SCATTERED MODERATE CONVECTION IS NEAR THE INTERSECTION
OF THE WAVE AXIS AND THE ITCZ. AN 850 MB VORTICITY MAXIMUM
SUPPORTS THE POSITION OF THE WAVE AXIS.

A TROPICAL WAVE IS ALONG 56W S OF 23N MOVING W NEAR 10 KT. SWLY
FLOW ASSOCIATED WITH AN UPPER-LEVEL LOW LOCATED TO THE WEST OF
THIS TROPICAL WAVE IS KEEPING MOST OF THE CONVECTION WELL BEHIND
OF THE WAVE AXIS FROM 16N-21N BETWEEN 48W-52W. UPPER DIFFLUENCE
AHEAD OF THIS UPPER TROUGH IS ALSO ENHANCING CONVECTION BETWEEN
THE TROPICAL WAVE AND THE WINDWARD ISLANDS.

A TROPICAL WAVE IS OVER THE NW CARIBBEAN AND CENTRAL AMERICA
ALONG 86 S OF 20N MOVING W 10-15 KT. THIS FEATURE IS GENERATING
ISOLATED MODERATE CONVECTION OVER THE NW CARIBBEAN...AND IS
HELPING TO INDUCE SCATTERED SHOWERS AND ISOLATED TSTMS OVER
PARTS OF HONDURAS AND NICARAGUA. THIS WAVE EXTENDS SOUTH INTO
THE EPAC.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 8N12W 7N25W 9N40W 11N53W 10N62W.
IN ADDITION TO CONVECTION ASSOCIATED WITH TROPICAL WAVES...
SCATTERED MODERATE CONVECTION IS FROM 3N-5N BETWEEN 24W-28W AND
WITHIN 50-60 NM EITHER SIDE OF AXIS BETWEEN 30W-34W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 2100 UTC...A COLD FRONT EXTENDS FROM SE LOUISIANA TO NEAR
TAMPICO MEXICO. AS SUGGESTED BY THE COMPUTER MODELS...A 1012 MB
SFC LOW HAS DEVELOPED OVER THE NORTH-CENTRAL GULF NEAR 27N90W
WITH A WARM FRONT EXTENDING MAINLY EWD ALONG 28N86W TO NEAR THE
TAMPA BAY AREA. MULTILAYERED CLOUDS WITH EMBEDDED SHOWERS COVER
THE NE QUADRANT OF THE GULF AND THE FLORIDA PANHANDLE N OF THE
WARM FRONT. ABUNDANT CLOUDINESS IS ALSO SEEN OVER THE SE GULF
AND THE FLORIDA PENINSULA. THE WARM FRONT SHOULD RAPIDLY LIFT
ACROSS THE NE GULF AND NORTHERN FLORIDA EARLY FRI AND WILL BE NE
OF THE AREA FRI AFTERNOON. AT THE SAME TIME...THE COLD FRONT IS
FORECAST TO MOVE SE AND MERGE WITH THE AFOREMENTIONED SFC LOW
PRES MOVING SLOWLY NE OVER THE SE CONUS. MODERATE TO STRONG NLY
WINDS ARE FOUND BEHIND THE COLD FRONT EXPECTED TO BE EXTENDED
FROM THE FLORIDA BIG BEND TO THE NE PORTION OF THE YUCATAN
PENINSULA FRIDAY MORNING. IN THE UPPER LEVELS...SOUTHWESTERLY
FLOW WITH CONSIDERABLE UPPER LEVEL MOISTURE PREVAILS OVER THE
GULF OF MEXICO. ADDITIONALLY...STRONG NORTHERLY WINDS BEHIND THE
COLD FRONT WILL BLOW THROUGH THE ISTHMUS OF TEHUANTEPEC AND
PRODUCE GALE FORCE GAP WINDS INTO  THE EASTERN PACIFIC REGION BY
TONIGHT.

CARIBBEAN SEA...
A TROPICAL WAVE IS OVER OVER THE NW CARIBBEAN...AND ANOTHER IS
APPROACHING THE LESSER ANTILLES. SEE TROPICAL WAVE SECTION.
FRESH TO STRONG TRADEWINDS ARE BLOWING OVER THE CARIBBEAN SEA.
IN THE UPPER LEVELS...A LARGE UPPER LEVEL HIGH CENTERED JUST
WEST OF JAMAICA DOMINATES THE ENTIRE BASIN AND CONTINUES TO
SUPPORT CONVECTION OVER THE NW CARIBBEAN AND CENTRAL AMERICA.
SUBSIDENCE/DRY AIR IS NOTED OVER THE EASTERN CARIBBEAN UNDER THE
INFLUENCE OF THIS UPPER HIGH...AND ONLY LOW TOPPED TRADE WIND
SHOWERS ARE SEEN. CONVECTION HAS FLARED-UP OVER NORTHERN
COLOMBIA LIKELY DUE TO THE COLOMBIAN OR PANAMANIAN LOW ANALYZED
1008 NEAR 8N75W. MODERATE TO ISOLATED STRONG CONVECTION IS
AFFECTING PARTS OF PANAMA AND COSTA RICA. THIS ACTIVITY APPEARS
TO BE ASSOCIATED WITH THE ITCZ.

ATLANTIC OCEAN...
A COLD FRONT ENTERS THE AREA NEAR 31N60W THEN CONTINUES MAINLY
WWD TO NORTH-CENTRAL FLORIDA NEAR 28N82W. A NARROW BAND OF
MAINLY LOW CLOUDS IS RELATED TO THIS FRONT. A STRONG HIGH PRES
CENTERED OVER THE NE CONUS IS BEHIND THE FRONT. PRES GRADIENT
BETWEEN THIS HIGH AND A BROAD AREA OF LOW PRES OVER THE GULF OF
MEXICO WILL PRODUCE GALE FORCE WINDS IN ABOUT 12-24 HOURS OVER
THE FAR NW PORTION OF THE FORECAST AREA. A SURFACE TROUGH...
REFLECTION OF AN UPPER-LEVEL LOW PERSISTS OVER THE CENTRAL
ATLANTIC ALONG 31N53W 25N54W. PATCHES OF LOW-LEVEL CLOUDS AND
MODERATE TRADE WINDS ARE OBSERVED OVER THE E ATLC LARGELY IN
PART TO A SURFACE RIDGE COVERING THE E ATLC E OF 40W. ALOFT...A
RIDGE/TROUGH/RIDGE/TROUGH PATTERN DOMINATES THE ENTIRE FORECAST
AREA. THE BROAD UPPER-LEVEL HIGH CENTERED OVER THE CARIBBEAN SEA
EXTENDS A RIDGE NWD ACROSS THE BAHAMAS INTO THE W ATLC. ABUNDANT
CLOUDINESS AND ISOLATED SHOWERS ARE ACROSS THE BAHAMAS AND THE W
ATLC WEST OF 70W AS DEEP TROPICAL MOISTURE STREAMS EAST FROM THE
EASTERN GULF OF MEXICO. AN UPPER-LEVEL LOW REMAINS OVER THE
CENTRAL ATLC NEAR 25N53W. THIS LOW HAS A TROUGH EXTENDING SW
INTO THE FAR SE CARIBBEAN THROUGH THE WINDWARD ISLANDS. UPPER
DIFFLUENCE BETWEEN THIS TROUGH AND A WEAK RIDGE TO THE EAST
CENTERED NEAR 30N38W IS GENERATING A WIDE BAND OF MULTILAYERED
CLOUDS WITH EMBEDDED SHOWERS AND POSSIBLE ISOLATED TSTMS BETWEEN
48W-53W FROM THE ITCZ TO 31N. ANOTHER UPPER LEVEL LOW IS
SPINNING OVER THE E ATLC NEAR 20N31W. A JET-STREAM BRANCH IS
AROUND THE BASE OF THIS TROUGH PRODUCING A BAND OF TRANSVERSE
HIGH CLOUDS WHICH EXTENDS FROM 10N35W ALL THE WAY NE CROSSING SE
OF THE CAPE VERDE ISLANDS INTO WEST AFRICA.

$$
GR