[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 180539
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 AM EST SAT 18 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0500 UTC.

...ITCZ...

ITCZ IS CENTERED ALONG 10N4W 5N30W 5N40W 4N60W 8N80W. NUMEROUS
MODERATE TO STRONG CONVECTION FROM 6N-9N BETWEEN 16W-26W.

...DISCUSSION...

GULF OF MEXICO...
THE PATTERN OVER THE GLFMEX REMAINS FAIRLY COMPLEX WITH MULTIPLE
WEAK FEATURES AFFECTING THE AREA.  IN THE UPPER LEVELS...A BROAD
LONGWAVE TROUGH REMAINS OVER THE E TWO-THIRDS OF THE UNITED
STATES WITH ASSOCIATED 120 KT S STEAM JET EXTENDING ACROSS THE
GLFMEX FROM NW MEXICO TO THE FLORIDA STRAITS. WATER VAPOR
IMAGERY SHOWS MULTIPLE SHORTWAVE IMPULSES EMBEDDED WITHIN THE
STRONG WLY FLOW MOVING QUICKLY EWD ACROSS THE AREA.  THE MOST
NOTABLE OF THESE DISTURBANCES IS CURRENTLY OVER THE CENTRAL
GLFMEX PRODUCING AN AREA OF CLOUDINESS AND SHOWERS/THUNDERSTORMS
OVER THE E GLFMEX AND FLORIDA.  THE STRONGEST OF THIS ACTIVITY
IS CURRENTLY FOCUSED ALONG AND TO THE N OF A STATIONARY FRONT
WHICH EXTENDS FROM THE FLORIDA STRAITS WESTWARD TO A WEAK
FRONTAL LOW NEAR 24N89W. A SECOND AREA OF CONVECTION IS NOTED
ALONG THE E COAST OF FLORIDA.  OVER THE W GLFMEX...HIGH PRESSURE
IS BUILDING SWD ALONG THE COAST OF MEXICO TO VERACRUZ WITH NLY
FLOW BANKED UP AGAINST THE SIERRA MADRE ORIENTAL MOUNTAINS. THIS
PATTERN IS PRODUCING OVERCAST LOW CLOUDS AND SHOWERS ALONG THE
WINDWARD FACING SLOPES OF MEXICO.  ELSEWHERE...SCATTERED SHOWERS
ARE OBSERVED ALONG A REMNANT FRONTAL TROUGH ALONG 26N EXTENDING
FROM S TEXAS EWD TO CENTRAL FLORIDA.  THE PATTERN WILL GRADUALLY
BECOME BETTER DEFINED DURING THE NEXT FEW DAYS AS CYCLOGENESIS
TAKES PLACE ALONG THE UNITED STATES E COAST SWEEPING THE
AFOREMENTIONED DIFFUSE FRONTAL BOUNDARY E OF THE AREA LATE SAT
INTO SUN.  THIS WILL RESULT IN STRONG NLY FLOW AND MUCH
COOLER/DRIER CONDITIONS OVER THE ENTIRE AREA BY SUN AFTERNOON.

CARIBBEAN...
BROAD UPPER LEVEL RIDGE REMAINS OVER THE CARIBBEAN EXTENDING
FROM PANAMA NEWD OVER HISPANIOLA INTO THE CENTRAL ATLC.
RESULTING FLOW IS PRIMARILY WLY WITH UPSTREAM PACIFIC MOISTURE
PASSING JUST N OF THE AREA.  MODERATE SUBSIDENCE AND DRY/STABLE
CONDITIONS CONTINUE ABOVE 600 MB WITH NO SIGNIFICANT DEEP
CONVECTION OVER THE AREA.  MOISTURE IS ALSO SCARCE AT THE LOWER
LEVELS SAVE A SMALL AREA OF SCATTERED SHOWERS ALONG A REMNANT
FRONTAL BOUNDARY FROM THE WINDWARD PASSAGE TO THE BORDER OF
COSTA RICA/PANAMA.  THIS ACTIVITY IS MOST NUMEROUS FROM JAMAICA
NEWD OVER E CUBA AND THE DOMINICAN REPUBLIC.  WEST OF THE
FRONT...LEFT OVER PATCHES OF CLOUDINESS AND ISOLATED SHOWERS DOT
THE AREA ESPECIALLY OVER THE GULF OF HONDURAS.

ATLANTIC...
MIDDLE TO UPPER LEVEL RIDGE IS BUILDING NWD OVER THE W ATLC AS A
TROUGH AMPLIFIES OVER THE E UNITED STATES. THIS IS PRODUCING AN
INCREASINGLY DIFFLUENT UPPER LEVEL PATTERN RESULTING IN THE
FORMATION OF A SURFACE TROUGH ALONG THE E COAST OF FLORIDA AND
NUMEROUS SHOWERS/THUNDERSTORMS FROM THE N BAHAMAS NWD TO 30N W
OF 76W.  SHIFTING EWD...A SHORTWAVE TROUGH OVER THE CENTRAL ATLC
HAS LIFTED NEWD ALLOWING THE ATTENDANT COLD FRONT TO BECOME
STATIONARY ALONG 32N50W 25N60W 20N70W.  WITH LITTLE UPPER LEVEL
SUPPORT...THE FRONT IS NOW QUICKLY WEAKENING WITH ONLY SCATTERED
SHALLOW TOPPED SHOWERS WITHIN 150 NM EITHER SIDE OF BOUNDARY.
OVER THE E ATLC...A BLOCKED HIGH OVER LOW TYPE REGIME PREVAILS
WITH A WELL-DEFINED ANTICYCLONE JUST N OF THE AREA NEAR THE
AZORES AND A UPPER TROUGH TO THE SOUTH FROM N MOROCCO WESTWARD
ACROSS THE CANARY ISLANDS TO 27N32W. MODERATE SUBSIDENCE AND
DRY/STABLE CONDITIONS PREVAIL ALONG THE TROUGH AXIS WITH A MORE
DIFFLUENT FLOW TO THE SOUTH SUPPORTING WIDESPREAD CLOUDINESS AND
SCATTERED MODERATE CONVECTION FROM THE ITCZ NWD TO 16N BETWEEN
20W-33W.  THIS ACTIVITY IS LIFTING NEWD AND WILL LIKELY
OVERSPREAD THE CAPE VERDE ISLANDS OVERNIGHT.

$$
RHOME




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