[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 092338
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST THU 09 DEC 2004

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN
SECTIONS OF SOUTH AMERICA...AND 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 2315 UTC.

...ITCZ...

AXIS OF ITCZ IS CENTERED ALONG 7N12W 5N20W 8N36W 7N41W 9N52W
9N62W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS WITHIN
60 NM OF THE AXIS FROM 30W-37W AND WITHIN 60 NM OF LINE 4N24W
7N27W. SCATTERED MODERATE CONVECTION IS WITHIN 60 NM OF THE
AXIS FROM 27W-29W...39W-42W...AND 48W-53W.

...DISCUSSION...

GULF OF MEXICO...
A POTENT SHORTWAVE TROUGH MOVING THROUGH THE CENTRAL UNITED
STATES IS THE BIGGEST WEATHER MAKER ACROSS THE AREA. GOOD UPPER
LEVEL DYNAMICS/LIFT AND AMPLE LOW LEVEL MOISTURE ASSOCIATED WITH
THIS SYSTEM IS PRODUCING SCATTERED SHOWERS OVER THE SE UNITED
STATES. A LINE OF SHOWERS/THUNDERSTORMS EXTENDS SW INTO THE GULF
OF MEXICO FROM THE WESTERN FLORIDA PANHANDLE TO THE CENTRAL GULF
NEAR 27N92W. THIS LINE IS ALONG A SURFACE TROUGH AHEAD A COLD
FRONT. THE FRONT STRETCHES FROM THE TENNESSEE VALLEY SWD OVER
SE LOUISIANA TO THE COAST OF MEXICO NEAR TAMPICO THEN AS A
STATIONARY FRONT OVER INTERIOR MEXICO ALONG THE E SLOPES OF THE
SIERRA MADRE ORIENTAL MOUNTAINS. THE FRONT IS MOVING VERY SLOWLY
AT THIS TIME.  A SECOND SHORTWAVE TROUGH CURRENTLY DROPPING SWD
INTO THE SOUTHERN PLAINS WILL FURTHER AMPLIFY THE PATTERN
SETTING UP A LARGE-SCALE TROUGH REGIME OVER THE E UNITED STATES
DURING THE NEXT 24-48 HOURS. THIS WILL ALLOW THE COLD FRONT TO
MOVE MUCH FASTER SE LATER TONIGHT AND FRI. THE FRONT IS FORECAST
TO REACH FROM CENTRAL FLORIDA TO THE YUCATAN PENINSULA BY FRI
NIGHT...THEN WILL CLEAR THE GULF OF MEXICO EARLY SAT. STRONG
HIGH PRESSURE IS EXPECTED TO BUILD IN BEHIND THE FRONT
SUPPORTING BRISK NLY FLOW AND MODERATE COLD AIR ADVECTION.  IN
FACT...THIS AIRMASS LOOKS TO BE ONE OF THE COOLEST THUS FAR IN
THE SEASON.

CARIBBEAN...
THE CARIBBEAN REMAINS HIGH AND DRY UNDER THE INFLUENCE OF STRONG
MIDDLE TO UPPER LEVEL RIDGING AND SUBSIDENCE.  A MIDDLE TO UPPER
CYCLONIC CIRCULATION OVER THE E PACIFIC ABOUT 150 NM SW OF THE
NW COAST OF COSTA RICA IS HELPING TO PRODUCE SCATTERED ITCZ
CONVECTION OVER PANAMA AND COSTA RICA.  OTHERWISE...DRY/STABLE
CONDITIONS PREVAIL IN THE MIDDLE TO UPPER LEVELS...ESPECIALLY E
OF 70W.  AREAS OF LOW LEVEL MOISTURE ARE PRODUCING SCATTERED
CLOUDS AND ISOLATED SHOWERS OVER THE CARIBBEAN S OF 17N
BETWEEN 70W-84W. MIDDLE TO UPPER LEVEL RIDGING WILL GRADUALLY
WEAKEN OVER THE NEXT COUPLE DAYS IN ADVANCE OF THE AMPLIFYING
TROUGH OVER THE E UNITED STATES AND GULF OF MEXICO.

ATLANTIC OCEAN...
LARGE SCALE ANTICYCLONE CENTERED OVER THE SE BAHAMAS DOMINATES
THE W ATLC WITH ASSOCIATED RIDGE EXTENDING NEWD INTO THE CENTRAL
ATLC ALONG 28N50W 28N40W.  THE RIDGE IS BEING PARTIALLY ERODED
BY A WEAK SHORTWAVE TROUGH DROPPING SWD ALONG 32N48W TO 29N54W.
THE RIDGE IS KEEPING THE W ATLC UNDER DRY/TRANQUIL CONDITIONS.

OVER THE CENTRAL ATLC...WATER VAPOR IMAGERY SUGGESTS THAT A
CUT-OFF UPPER LOW HAS FORMED NEAR 20N50W. A TROUGH EXTENDS SW
FROM THE CIRCULATION TO 12N58W...JUST SE OF THE WINDWARD ISLANDS.
MODERATE/STRONG SUBSIDENCE/DRY AIR IS LOCATED ALONG AND WEST
OF THE CYCLONIC CIRCULATION AND TROUGH. OVER THE EASTERN ATLC A
LARGE MID/UPPER LEVEL ANTICYCLONIC CIRCULATION IS CENTERED NEAR
7N24W. BROAD ANTICYCLONIC FLOW COVERS THE EASTERN ATLC S OF 24N
E OF THE UPPER LOW. THIS PATTERN IS PRODUCING DIFFLUENT MIDDLE
TO UPPER LEVEL FLOW TO THE EAST OF THE UPPER LOW AND SUPPORTING
WIDESPREAD CLOUDINESS AND SCATTERED SHOWERS/ISOLATED
THUNDERSTORMS FROM THE ITCZ NWD TO 22N BETWEEN THE CAPE
VERDE ISLANDS AND 48W.  THE STRONGEST AND MOST NUMEROUS
SHOWER/THUNDERSTORM ACTIVITY IS LOCATED FROM 10N-20N BETWEEN
33W-45W.  THIS AREA SHOULD REMAIN UNSETTLED OVER THE NEXT FEW
DAY OR SO AS THE UPPER LOW REMAINS NEARLY STATIONARY. OVER THE
FAR NE PORTION OF THE AREA...A FAST-MOVING SHORTWAVE TROUGH IS
MOVING SE TOWARDS THE AZORES AND THE COAST OF AFRICA.

$$
BROWN



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